# 0. Contents

  1. About
  2. Commandline Options

  Options -0, -1, -2, ..., -10
  Option -bin
  Option -coff
  Option -djgpp
  Option -e
  Option -elf
  Option -elf64
  Option -eq
  Option -Fd
  Option -FPi
  Option -Fw
  Options -Gc, -Gd, -Gr, -Gz
  Option -m
  Option -mz
  Option -nc
  Options -nd, -nt
  Option -nm
  Option -pe
  Option -win64
  Option -zc
  Option -Zd
  Option -zf
  Option -Zg
  Option -Zi
  Options -zlc and -zld
  Options -zlf, -zlp and zls
  Option -Zm
  Option -Zne
  Option -zt
  Option -Zv8
  Option -zze
  Option -zzs

  3. Syntax Extensions

  3.1 Directive INCBIN
  3.2 FASTCALL Register Calling Convention
  3.3 IDs enclosed in Back Quotes
  3.4 Floating-Point Immediates in Instructions
  3.5 Directive OPTION FIELDALIGN
  3.6 Directive OPTION PROCALIGN
  3.7 Directive OPTION MZ
  3.8 Directive OPTION ELF
  3.9 Directive OPTION WIN64
  3.10 Directive OPTION FRAME
  3.11 Directive OPTION RENAMEKEYWORD
  3.12 Directive OPTION DLLIMPORT
  3.13 Directive OPTION CODEVIEW
  3.14 Directive OPTION STACKBASE
  3.15 Directives PUSHCONTEXT / POPCONTEXT ALIGNMENT
  3.16 Directives .X64 and .X64p
  3.17 Attribute LABEL for first Macro Parameter
  3.18 Member Argument for IF[N]DEF and .ERR[N]DEF
  3.19 Initialization of Data Items of Type MMWORD/XMMWORD
  3.20 Optional Array Size for LABEL Directive
  3.21 Optional Name Argument for Simplified Segment Directives
  3.22 Segment Attribute COMDAT
  3.23 Attribute VARARGML for last Macro Parameter
  3.24 Miscellaneous

  3.24.1 Numeric constant __JWASM__
  3.24.2 Operating System Argument for .MODEL
  3.24.3 Accepted Parameters for IF[N]DEF Directive
  3.24.4 Visibility of Procedures
  3.24.5 Non-RIP-Relative Addressing in 64-Bit

  4. Instruction Sets
  5. Code Generation Differences

  5.1 Forward References in Macro Expressions

  6. Output Formats

  6.1 OMF Output Format
  6.2 COFF Output Format
  6.3 Win64 Output Format
  6.4 Binary Output Format
  6.5 PE Output Format

  7. Masm Bugs fixed in JWasm
  8. Optional Features
  9. Known Bugs and missing Features
  10. License
  Appendix A. Reserved Words
  Appendix B. Source Samples
  Appendix C. Errors and Warnings
  Appendix D. Differences between Masm 6 and Masm 8
  Appendix E. Restrictions of precommpiled 16-bit Binary JWASMR.EXE
  Appendix F. Additional Features of JWasm's Debug Version

# 1. About

This document lists the differences between JWasm and Masm, as far as the user interface is concerned.

When Masm is mentioned, then usually Masm v8.00 is meant, unless stated otherwise. Masm v8.00 also was the first Masm version supporting 64-bit (ML64.EXE).

The Masm documentation itself can be found on numerous places in the web, in plain text, HTML, PDF and Windows Help format. However, it's usually just the documentation that came whith Masm v6.1 - hence a bit outdated nowadays ( the changes from Masm v6 to Masm v8 are listed in Appendix D ).

# 2. Commandline Options

Entering 'JWasm -?' or 'JWasm -h' will make JWasm display the options it understands. A lot of them exist in both Masm and JWasm, but some are valid for JWasm only; OTOH, a few options are missing in JWasm.

Options are usually entered via the command line. Additionally, when starting, JWasm will search for environment variable JWASM and handle it similar to the way Masm handles variable ML. Hence it is also possible to enter options via this method.

The options specific to JWasm - and also the options which are handled somewhat differently by JWasm compared to Masm - will be handled in the following chapters.

One major difference should be mentioned here: JWasm does never launch a linker on its own ( which Masm does unless option -c is given ). This makes a few Masm options useless for JWasm, and hence they are not implemented; see Chapter Known Bugs and missing Features for details.

## Options -0, -1, -2, ..., -10: Select Cpu

Option [0|1|..|10] selects cpu/instruction set. Most values correspond to cpu directives:

0 | .8086
1 | .186
2 | .286
3 | .386
4 | .486
5 | .586
6 | .686
7 | .686 and .MMX (P2)
8 | .686, .MMX and SSE instructions (P3)
9 | .686, .MMX, SSE and SSE2 instructions (P4)
10 | .x64 (x86-64 cpu)

## Option -bin: Select Output Format Binary

Option -bin selects output format BINary. The output module's default file extension will be changed from .OBJ to .BIN.

For more information, see Binary Output Format.

Chapter Output Formats lists all available output formats.

## Option -coff: Select Output Format COFF

Option -coff selects output format COFF. The most common use for -coff is to produce modules for 32-bit Windows. However, it's not mandatory that the output will be 32-bit with -coff; depending on what cpu is selected when the .MODEL directive will be parsed, the output may be 32- or 64-bit.

For more information about COFF, see COFF Output Format.

Chapter Output Formats lists all available output formats.

## Option -djgpp: Select Output Format for DJGPP (optional)

Option -djgpp selects Djgpp's variant of COFF as output format.

Chapter Output Formats lists all available output formats.

## Option -e: Set error limit

Allows to set the number of errors after which the assembly process is aborted. The default value is 50.

## Option -elf: Select 32-bit Output Format ELF

Option -elf selects output format ELF. JWasm will produce an object module in 32-bit Elf format.

Use OPTION ELF to set values in the ELF header.

Chapter Output Formats lists all available output formats.

## Option -elf64: Select 64-bit Output Format ELF

Option -elf64 selects output format ELF64. JWasm will produce an object module in 64-bit Elf format. Additionally, this option will set cpu to x86-64 and model to FLAT.

Use OPTION ELF to set values in the ELF header.

Chapter Output Formats lists all available output formats.

## Option -eq: Suppress Error Messages on Screen

Option -eq will suppress displaying error messages on the screen. They are still written into an error file.

## Option -Fd: Write Import Definitions

Option -Fd makes JWasm write import definitions in a format understood by Open Watcom's Wlink and JWlink. Such definitions will tell the linker how to resolve the external reference; no import library is needed. This option is only useful in conjunction with OPTION DLLIMPORT (chapter 3.12). Syntax is:

  -Fd[=file_name]

If the optional <file_name> argument is given, the import definitions will be written into a file of this name. This is the only way for Open Watcom's Wlink to pass the information.

If JWlink is used, the <file_name> argument may be omitted. Then JWasm will write the import definitions directly into the object module's linker directive section (section ".drectve"). This works for output formats COFF and ELF only. See sample Win32_7 how to use JWasm and JWlink to create a Windows binary without import libs.

## Option -FPi: Activate Floating-Point Emulation

Option -FPi activates "inline FP instructions with emulation". This will make JWasm create fixups for floating-point instructions if code is 16bit. If supported by the linker or the OS, the FP instructions can then be replaced by calls to an FP emulator if no coprocessor exists.

## Option -Fw: Set Error File Name

Option -Fw will set the file name for warning and error messages. As default, these messages are written to a file with a name equal to the assembly source, but with extension .ERR. Syntax is:

  -Fw file_name

## Options -Gc, -Gd, -Gr, -Gz: Set Default Calling Convention

The default calling convention set by these options are:

-Gc | Pascal
-Gd | C(decl)
-Gr | Fastcall
-Gz | Stdcall

## Option -m: Select Memory Model

Option -m generates a line containing a .MODEL directive to select a memory model. Syntax is:

  -m[t|s|m|c|l|h|f]

where the value behind 'm' means:

  t = tiny
  s = small
  m = medium
  c = compact
  l = large
  h = huge
  f = flat

This option is ignored if a 64-bit output format (-win64 or -elf64) is active.

## Option -mz: Select Output Format MZ

Option -mz selects output format MZ. This will write a binary in DOS MZ format. The module's default file extension will be changed from .OBJ to .EXE. All symbols in the module must resolve internally, no externals are allowed. Some values in the "MZ" header can be adjusted by directive OPTION MZ (see below).

As in all binary formats, the listing will contain a binary map; see Binary Output Format for more details.

Chapter Output Formats lists all available output formats.

## Option -nc: Set Code Class Name

Option -nc sets the code segment's class name if simplified segment directives are used (default:CODE). Syntax is:

  -nc=name

where <name> will be the code segment's class name.

## Options -nd and -nt: Set DATA and CODE Segment Names

Options -nd and -nt will set the name of the data/code segments if simplified segment directives are used. Syntax is:

  -nt=name_of_code
  -nd=name_of_data

The default names are _TEXT for code and _DATA for data.

## Option -nm: Set Module Name

Option -nm sets the module name. Syntax is:

  -nm=module_name

The default value for <module_name> is the name of the source file without extension.

## Option -pe: Create a PE Binary

Option -pe will make JWasm create a binary in Windows PE format (32- and 64-bit). The output module's default file extension will be changed from .OBJ to .EXE.

For more details about the PE format see PE Output Format.

Chapter Output Formats lists all available output formats.

## Option -win64: Select Output Format Win64

Option -win64 makes JWasm produce an object module in PE32+ format, the 64-bit format used for Win64 binaries.

Option -win64 will also set cpu to x86-64, model to FLAT and default calling convention to FASTCALL. This is to make JWasm compatible with Masm64 (ML64.EXE).

With OPTION WIN64, parameters specific to Win64 may be set.

For more information about Win64, see Win64 Output Format.

Chapter Output Formats lists all available output formats.

## Option -zc: Set Name Decoration for C

This option sets the name decoration for the C ( aka CDECL ) calling convention. There are two variants:

  -zc[m|w]

-zcm is the default, C names are decorated with an underscore prefix. This is also the way Masm does it. The other variant, -zcw, omits the prefix altogether. This is the usual "decoration" in Unix/Linux.

## Option -Zd: Emit Line Number Debugging Info

Option -Zd generates line number debug information for OMF and COFF output format. For other formats, this option is ignored. Line number information allows a debugger to trace the binary on the source code level. Debuggers that have been verified to work with this option:

MS CodeView | OMF | 16-bit, Windows and DOS
CDB, NTSD | COFF | 32- and 64-bit, Windows
WinDbg | COFF | 32- and 64-bit, Windows
MS Visual Studio 2008 | COFF | 32-bit[1], Windows
MS Visual Studio 2010 | COFF | 32-bit[1], Windows
OW WD/WDW | OMF/COFF | 16- and 32-bit, Windows and DOS
PellesC IDE | COFF | 32-bit[1], Windows
Borland TD/TDW/TD32 | OMF | 16- and 32-bit, Windows and DOS

[1]: the 64-bit version of this software should also be able to debug 64-bit debuggees.

## Option -zf: Select FASTCALL Type

Option -zf selects the FASTCALL calling convention type for 16- and 32-bit code. Syntax is:

  -zf[0|1]

The default value 0 is MS VC style, while value 1 activates the Open Watcom fastcall type.

## Option -Zg: Masm-compatible Code Generation

Option -Zg makes JWasm try an exact copy of Masm's code generation, which results in the following changes:

- the default prologue for procedures will use
  `add [e]sp, - localsize`
  instead of
  `sub [e]sp, localsize`.
- the default epilogue for procedures will almost always prefer to generate opcode `LEAVE` if possible.
- expressions
  `<reg> == 0` and `<reg> != 0`
  will generate code
  `or <reg>,<reg>`
  instead of
  `cmp <reg>,0`.
- if invoke must extend an argument's size from word to dword, register eax remains unchanged.
- the segment value of FAR externals will always be assumed unknown, no matter whether the external is defined inside or outside of a segment block. Thus those labels are excluded from "far call optimization".
- if indirect addressing uses 2 (32- or 64-bit) registers and no scaling factor is used and the second register isn't ESP/RSP, then the registers are swapped: the second becomes base and the first becomes index ( the registers in an expression are counted from left to right ). [ since v2.10, this is standard behavior ].
- OPATTR will return the language type bits 8-10 for PROCs and PROTOs only.

## Option -Zi: Emit Symbolic Debugging Info

Option -Zi generates symbolic debugging info in CodeView V4 style for OMF and COFF output format. For other formats, this option is accepted, but ignored. Note that -Zi will always enable -Zd ( line number information ). Debuggers which have been verified to work with this option:

MS CodeView | 16-bit, Windows and DOS
MS CDB or NTSD | 32- and 64-bit, Windows
MS WinDbg | 32- and 64-bit, Windows
MS Visual Studio 2008 | 32-bit[1], Windows
MS Visual Studio 2010 | 32-bit[1], Windows
Open Watcom WD/WDW | 16- and 32-bit, Windows and DOS
Pelles C IDE | 32-bit[1], Windows

[1]: the 64-bit version of this software should also be able to debug 64-bit debuggees.

Usually both the assembler and the linker must be told that symbolic debugging information is to be generated ( with MS link, the linker option is /DEBUG ).

The -Zi option accepts an optional numeric argument to control the volume of information that is emitted. The values currently accepted are:

0 | Just global symbols will be written.
1 | Global & local symbols will be written. No user-defined types are included. Usually this reduction does no harm, but may decrease linking time - if lots of modules are to be linked, the effect may be quite significant.
2 | This is the default. Global & local symbols and user-defined types are written.
3 | Additionally to 2, symbolic constants (equates) will be written.

Also see OPTION CODEVIEW for additional switches to control symbolic debugging output.

## Options -zlc and -zld: Control Content of OMF Output Module

Options -zlc and -zld do reduce size of the OMF output module. They might be useful if lots of - small - modules are to be assembled and put into a static library. Also, the OMF coment records written if -zlc or -zld is NOT set may not be accepted by all linkers.

Option -zlc:
  suppresses writing OMF coment records about data in Code segments. These records may help a disassembler to produce nicer listings.
Option -zld:
  suppresses writing an OMF coment record for each Code segment telling the linker that far calls to targets in the same segments should be optimized. This is more or less a feature for 16-bit code only.

## Options -zlf, -zlp and -zls: Control Content of COFF Output Module

Options -zlf, -zlp and -zls do reduce size of the COFF output module. They might be useful if lots of - small - modules are to be assembled and put into a static library.

Option | Meaning
-zlf | suppresses the @file entry in the COFF symbol table. This entry is usually used for debugging purposes only and hence a - pretty small - amount of space can be saved.
-zlp | suppresses static (=private) procedures to be included into the COFF symbol table - as long as they aren't referenced absolutely. Such procedures aren't needed for the linking process. However, since the linker has no knowledge of them then, they will also disappear from the linker-generated map-file.
-zls | suppresses the auxiliary entries for sections in the COFF symbol table. These entries may not be needed in all cases and thus a little space is saved.

## Option -Zm: Enable Masm v5 Compatibility

Option -Zm (or setting OPTION M510) will do:

  - set OPTION OLDSTRUCTS
  - set OPTION DOTNAME
  - set OPTION SETIF2:TRUE
  - set OPTION OFFSET:SEGMENT (if no model is set)
  - set OPTION NOSCOPED (if no model with language specifier is set)
  - allow to define data items behind code labels
  - allow "invalid" use of REP/REPE/REPNE instruction prefixes
  - change precedence of [] and () operator from 1 to 9. Hence expression -5[bx] is parsed as (-5)[bx], while without -Zm it is parsed as -(5[bx]), which generates an error.

Other Masm v5.1 compatibility options aren't implemented yet.

## Option -Zne: Disable JWasm Syntax Extensions

Option -Zne will disable syntax extensions which aren't supported by Masm. Currently these are:

  - directive INCBIN
  - calling convention FASTCALL
  - IDs enclosed in backquotes
  - floating-point immediate operands in instructions
  - directive OPTION FIELDALIGN
  - directive OPTION PROCALIGN
  - directive OPTION MZ
  - directive OPTION ELF
  - directive OPTION WIN64
  - directive OPTION FRAME
  - directive OPTION RENAMEKEYWORD
  - directive OPTION DLLIMPORT
  - directive OPTION CODEVIEW
  - directive OPTION STACKBASE
  - directives PUSHCONTEXT / POPCONTEXT ALIGNMENT
  - attribute LABEL for first macro parameter
  - member argument for IF[N]DEF and .ERR[N]DEF directives
  - integer initializer values for items of type [X]MMWORD
  - optional name argument for .DATA, .DATA? and .CONST directives
  - forward references in arguments for INVOKEd procedures
  - overrides inside square brackets for base/index registers
  - Optional Array Size for LABEL Directive

Some directives aren't touched by this option, although Masm won't accept them:

  .X64 and .X64p
  INVOKE in 64-bit mode
  runtime conditional directives .IF, .REPEAT, .WHILE in 64-bit mode

If these directives are to be disabled, it must be done with OPTION NOKEYWORD.

## Option -zt: Set Name Decoration for STDCALL

Option -zt will fine-tune name decoration for STDCALL symbols. Syntax is:

  -zt[0|1|2]

where value 0 will disable name decoration, value 1 will just add an underscore prefix and value 2 - which is the default - will emit full STDCALL name decoration as expected by most linkers.

Option -zt0 will make object modules compatible to ALINK + Win32.lib. It may also ease adding assembly modules to Borland's C++Builder or Delphi projects.

## Option -Zv8: Enable Masm v8 Procedure Visibility

Option -Zv8 changes handling of procedure visibility to the way done by Masm v8+. See Visibility of Procedures for details.

## Option -zze: Disable Export Name Decoration

Option -zze suppresses name decoration for procedures with the EXPORT attribute (exported name only).

## Option -zzs: Avoid Wlink COFF Incompatibility

Option -zzs is kind of a workaround for a Wlink incompatibility. It's useful to be set if 1) the source module has a starting address, 2) output format is COFF AND 3) Wlink is to be used as linker.

# 3. Syntax Extensions

This chapter describes the syntax extensions of JWasm compared to Masm v8.

## 3.1 Directive INCBIN

This directive allows to include the contents of a file into the object module. Syntax is

  INCBIN filename [, starting offset[, max size]]

<filename> should be enclosed in <> or double quotes.

## 3.2 FASTCALL Register Calling Convention

In 16- and 32-bit mode, one may use either the Microsoft or the Watcom register calling convention. It's selected by option -zf.

The Microsoft FASTCALL convention uses registers AX, DX and BX in 16-bit for the first 3 parameters, and registers ECX and EDX in 32-bit for the first 2 parameters which are small enough to fit into a register.

The Open Watcom fastcall convention uses up to four registers ( E/AX, E/DX, E/BX, E/CX ).

In 64-bit mode, FASTCALL means the standard Windows 64 ABI if output format is not ELF. For -elf64, there is no FASTCALL support implemented yet.

To make FASTCALL the default calling convention, there are 3 ways:

- Commandline options -Gr ( or -win64 )
- Second argument of the .MODEL directive: .MODEL FLAT, FASTCALL
- Directive OPTION LANGUAGE: FASTCALL

## 3.3 IDs enclosed in Back Quotes

IDs can be enclosed in back quotes (`) and thus they can contain characters not allowed in "normal" IDs. However, there is at least one case where IDs in back quotes won't be recognized: if the expansion operator (%) is located at position 0 in a line.

Example using back quotes:

Module 1:

        `functionname.with.dots` PROC C PUBLIC a1:dword

Module 2:

        `functionname.with.dots` PROTO C :dword
        .code
        INVOKE `functionname.with.dots`, 1

Since IDs in back quotes are not 100% compatible with "normal" IDs, it might be considered to use the ALIAS directive instead. Be aware that, since the alias handling is a linker task, it is necessary to define both names, the alias name and the target name, as public.

## 3.4 Floating-Point Immediates in Instructions

Floating-point immediate values are accepted as instruction operands. As default, the type is a REAL4, which has a magnitude of 32 bits:

            mov eax, 1.0

With type coercion, it's also possible to define a 64-bit "double", although it's probably useful in 64-bit code only:

            mov rax, real8 ptr 1.0

Additionally, operators LOW32 and HIGH32 accept a floating-point constant as argument. In this case, the constant is assumed to have format REAL8. Thus it's possible to pass a double constant directly as a procedure argument in 32-bit code:

           push HIGH32 1.0
           push LOW32 1.0
           call WorkWithReal8Value

## 3.5 Directive OPTION FIELDALIGN

OPTION FIELDALIGN sets the default value for structure alignment. The default value is 1 or the value set by cmdline switch -Zp. Syntax is:

  OPTION FIELDALIGN: [1|2|4|8|16|32]

The current default value can be saved/restored with directives PUSHCONTEXT / POPCONTEXT ALIGNMENT,

## 3.6 Directive OPTION PROCALIGN

With OPTION PROCALIGN parameter it's possible to automatically align procedures. Syntax is:

  OPTION PROCALIGN: [1|2|4|8|16|32]

The default value is 1. The current value can be saved/restored with directives PUSHCONTEXT / POPCONTEXT ALIGNMENT,

Example:

        .386
        .model flat, stdcall
        option PROCALIGN:16
        .code

    proc1 PROC
        ret
    proc1 endp

    proc2 PROC
        ret
    proc2 endp

        end

The listing shows that start address of proc2 is aligned to 16 (=10h):

    00000000                        proc1 PROC
    00000000                            ret
    00000000  C3                *   retn
    00000001                        proc1 endp

    00000010                        proc2 PROC
    00000010                            ret
    00000010  C3                *   retn
    00000011                        proc2 endp

Note: to ensure that the procedures are aligned in the final binary as it is supposed by the OPTION PROCALIGN value, the alignment of the current code segment must be at least the value of OPTION PROCALIGN.

## 3.7 Directive OPTION MZ

Directive OPTION MZ allows to fine-tune the values written to the MZ header if output format MZ (see -mz cmdline option) is selected. For other output formats, this option has no effect. The syntax for the directive is:

  OPTION MZ:[start_fixups][:header_align][:heap_min][:heap_max]

The parameters are:

start_fixups | offset within the header where segment fixups will start. The size of the header will always be at least this value, even if there are no fixups at all. Default - and minimum - value is 1Eh.
header_align | alignment of the header (including segment fixups). Value must be a power of 2, 10h is the default and minimum.
heap_min | the additional space (in paragraphs) which is needed by the binary to run. Default is the total of the sizes of the uninitialized BSS and STACK segments.
heap_max | space (in paragraphs) which the binary would like to have. Default is FFFFh.

## 3.8 Directive OPTION ELF

Directive OPTION ELF allows to fine-tune the values written to the ELF header if output format ELF (see -elf or -elf64) is selected. For other output formats, this option has no effect. The syntax for the directive is:

  OPTION ELF:osabi

The only argument <osabi> will be copied to the ELF header field EI_OSABI. It's a numeric constant, and according to the elf specs some valid values are:

0 | ELFOSABI_NONE | unspecified
1 | ELFOSABI_HPUX | HP-UX
2 | ELFOSABI_NETBSD | NetBSD
3 | ELFOSABI_LINUX | Linux, default
6 | ELFOSABI_SOLARIS | Sun Solaris
7 | ELFOSABI_AIX | IBM AIX
9 | ELFOSABI_FREEBSD | FreeBSD
12 | ELFOSABI_OPENBSD | OpenBSD

## 3.9 Directive OPTION WIN64

Directive OPTION WIN64 allows to set parameters for the Win64 output format if this format (see -win64 cmdline option) is selected. For other output formats, this option has no effect. The syntax for the directive is:

  OPTION WIN64: switches

accepted values for switches are:

  Store Register Arguments [ bit 0 ]:
  - 0: the "home locations" (also sometimes called "shadow space") of the first 4 register parameters are uninitialized. This is the default setting.
  - 1: register contents of the PROC's first 4 parameters (RCX, RDX, R8 and R9 ) will be copied to the "home locations" within a PROC's prologue.

  INVOKE Stack Space Reservation [bit 1]:
  - 0: for each INVOKE the stack is adjusted to reserve space for the parameters required for the call. After the call, the space is released again. This is the default setting.
  - 1: the maximum stack space required by all INVOKEs inside a procedure is computed by the assembler and reserved once on the procedure's entry. It's released when the procedure is exited. If INVOKEs are to be used outside of procedures, the stack space has to be reserved manually!
  Note: an assembly time variable, @ReservedStack, is created internally when this option is set. It will reflect the value computed by the assembler. It should also be mentioned that when this option is on, and a procedure contains no INVOKEs at all, then nevertheless the minimal amount of 4*8 bytes is reserved on the stack.
  Warning: You should have understood exactly what this option does BEFORE you're using it. Using PUSH/POP instruction pairs to "save" values across an INVOKE is VERBOTEN if this option is on.

  16-byte Alignment for Local Stack Variables [bit 2]:
  0: standard 8-byte alignment for local variables.
  1: 16-byte alignment for local variables. This setting is useful if you want to load or store XMM registers with instructions that expect aligned memory references ( i.e. MOVAPS ). Note that variables with size < 16 are not affected.

## 3.10 Directive OPTION FRAME

This option affects 64-bit only. It allows to make JWasm automatically generate prologues and epilogues for procedures with the FRAME attribute. Thus the code complies to the rules of Win64 SEH (Structured Exception Handling). Syntax is

  OPTION FRAME:<AUTO | NOAUTO>

AUTO will enable this feature, NOAUTO (which is default) disables it.

The unwind information which is generated is "complete", that is, it contains the ".endprologue" pseudo-op already. To allow to save all non-volatile registers in the prologue, the "USES" phrase is more capable in this mode and will accept XMM registers to be saved and restored.

## 3.11 Directive OPTION RENAMEKEYWORD

This option allows to rename a keyword, so it can be used under a different name. Syntax:

  OPTION RENAMEKEYWORD:<current_name>=new_name

current_name is the current name of the keyword and must be enclosed in angle brackets. new_name must be a valid identifier. If a keyword is to be renamed, it should be done at the beginning of the source, and a keyword shouldn't be renamed multiple times. Since v2.11, a keyword may be renamed temporarily and multiple times.

## 3.12 Directive OPTION DLLIMPORT

### a) Using OPTION DLLIMPORT

This option makes the assembler assume that all PROTOs that follow this directive represent functions located in a dll. Syntax:

  OPTION DLLIMPORT:<dll_name> | NONE

<dll_name> must be enclosed in angle brackets. Argument NONE will switch back to the default mode.

### b) Code Generation Effects

The effects of setting this options are subtle and useful only for MS Windows applications: if the function described by the prototype is called via INVOKE, slightly more efficient code than normal is generated, because the function's address in the IAT is used. Example:

  INVOKE GetModuleHandle, NULL

code generation with OPTION DLLIMPORT:

            push NULL
            call DWORD PTR [_imp__GetModuleHandle@4]

code generation without OPTION DLLIMPORT:

            push NULL
            call _GetModuleHandle@4
            ...
        _GetModuleHandle@4:
            jmp DWORD PTR [_imp__GetModuleHandle@4]  ;stub added by the linker

### c) OPTION DLLIMPORT in Conjunction with -Fd Switch

Optionally, by using cmdline option -Fd, JWasm will write the import information received through OPTION DLLIMPORT lines to either a file or directly into the object module (COFF and ELF only). Example:

            .386
            .model flat,stdcall
            option dllimport:<kernel32>
        GetModuleHandleA proto :dword
        ExitProcess proto :dword
            option dllimport:none
            .code
            invoke GetModuleHandleA, 0
            invoke ExitProcess, 0
            end

  JWasm -coff -Fd=lnk.rsp sample.asm

After the assembly step, file lnk.rsp will contain:

  import '_ExitProcess@4' kernel32.ExitProcess
  import '_GetModuleHandleA@4' kernel32.GetModuleHandleA

Both Open Watcom's Wlink and JWlink will be able to directly use this information and hence, as a result, no further Windows import libraries are needed in the link step:

  Wlink format windows pe file sample.obj @lnk.rsp

JWlink may even go one step further - it's able to read import definitions contained in a COFF or ELF module's linker directive section ( named ".drectve" ). Therefore one can omit the filename argument for -Fd. Sample Win32_7 demonstrates the usage.

### d) OPTION DLLIMPORT in Conjunction with -pe Switch

If output format PE is selected, using OPTION DLLIMPORT is the only way to resolve external references; see PE Output Format for more information.

## 3.13 Directive OPTION CODEVIEW

The OPTION CODEVIEW directive allows to fine-tune the generation of symbolic debugging information. It has no effect at all if commandline option -Zi isn't set. Syntax:

  OPTION CODEVIEW:switches

There is currently only one switch :

  [bit 0]: If 1, create symbols with indices S_[L|G]THREAD32 instead of S_[L|G]DATA32 for data items that are stored in segments with class 'TLS'. This allows the debugger to display the correct value of static TLS ( Thread Local Storage ) variables. Example:

          option codeview:1

      _TLS segment dword alias(".tls") public 'TLS'
      tvar DD -1      ;codeview symbol tvar will be S_LTHREAD32
      _TLS ends

## 3.13 Directive OPTION STACKBASE

The OPTION STACKBASE directive allows to change the way how stack variables - defined by the PROC and LOCAL directives - are accessed. Syntax is:

  OPTION STACKBASE:register

register will be the index register that is used for accessing the stack variables. The "natural" register for accessing these variables is the [E|R]BP register ( the "frame pointer"). With OPTION STACKBASE one might set any index register as frame pointer.

Besides the goal "frame pointer omission" in 64-bit, OPTION STACKBASE may also be used in 16- and 32-bit code to make directives PROC and INVOKE handle stack variables correctly when the code and stack segment in protected-mode differ in offset magnitude ( 16-bit code running on a 32-bit stack and vice versa ).

OPTION STACKBASE will additionally define assembly-time variable @StackBase. The assembler will add the value of this variable to the effective address of stack variables. @StackBase can be modified just like any userdefined variable - however, it is initialized to zero by the PROC directive. The purpose for the introduction of @StackBase is to make it feasible to use the "volatile" stack-pointer (ESP/RSP) register as base for accessing stack variables.

Finally, OPTION STACKBASE will define another assembly-time variable: @ProcStatus. This variable is read-only and will allow to query information about the current procedure's status. The information that is returned by @ProcStatus is:

Bit | Meaning if bit is 1
0 | inside prologue of current procedure.
1 | inside epilogue of current procedure.
2 | "frame-pointer omission" is on for procedure
7 | prologue of current procedure isn't created yet

## 3.15 Directives PUSHCONTEXT / POPCONTEXT ALIGNMENT

The PUSHCONTEXT / POPCONTEXT directives understand new qualifier ALIGNMENT, which saves/restores current values of FIELDALIGN and PROCALIGN options.

Note: in JWasm v2.00-2.09, PUSHCONTEXT / POPCONTEXT ALL did include these alignment values. Since JWasm v2.10, this is no longer true; this behavior is more Masm-compatible.

## 3.16 Directives .X64 and .X64p

These directives select a 64-bit (x86-64) cpu. In contrast to .X64, .X64p will allow to use privileged instructions.

The .X64 directive isn't needed usually, because for output formats WIN64 (see -win64) and ELF64 (see -elf64), .X64 is the default.

The .X64p directive is useful for mixed-model binaries or system software (see example DOS64 ).

When the cpu is set to 64-bit, the SEGMENT directive accepts a new 'size' value: USE64. It tells the assembler that this segment's offset is 64-bit wide and uses 64-bit instructions.

The SYSCALL calling convention is renamed to SYSCALL_ when 64-bit is on, because there exists a SYSCALL instruction mnemonic in this mode.

## 3.17 Attribute LABEL for first Macro Parameter

The LABEL attribute for the first macro parameter allows access to a label which is assigned to the macro. Syntax is:

<macro_name> MACRO <param_name>:LABEL [,<param_name>[, ...]]

The LABEL attribute is accepted for the first parameter only. A macro with such a parameter can be invoked in the following way:

<label> <macro_name> [<argument>, ...]

Example:

        foo macro lbl:LABEL, first, second
        lbl  db first
             dw second
        endm

        .data

        data1 foo 1,1000
        data2 foo 2,2000

Note that a code label ( that is, a label followed by a colon or double-colon ) is parsed BEFORE the macro is evaluated, hence such a label will have been defined already when the macro "runs".

## 3.18 Member Argument for IF[N]DEF and .ERR[N]DEF Directives

Since v2.07, JWasm's implementation of IF[N]DEF - and .ERR[N]DEF - will additionally accept a struct member as argument. This syntax requires a fully qualified name:

          IFDEF <struct_name>.<member_name>

## 3.19 Initialization of Data Items with Type MMWORD/XMMWORD

For data items of types MMWORD or XMMWORD, JWasm will accept integer values for initialization:

        vmm1  MMWORD  1122334455667788h
        vxmm1 XMMWORD 112233445566778899AABBCCDDEEFFh

Masm will accept just floating-point initializers for data items of type [X]MMWORD. It's even worse, since floating-point initializers are silently ignored for data items with sizes != 4, 8 and 10; since XMMWORD has size 16, it's impossible to initialize such an item directly. JWasm copies this Masm behavior, but to allow to initialize a XMMWORD with a floating-point value, one may use type coercion:

        vxmm1 XMMWORD real4 ptr 1.0   ;bytes 4-15 will be 0
        vxmm2 XMMWORD real8 ptr 1.0   ;bytes 8-15 will be 0

Variants that work in both JWasm and Masm, and also allow to initialize the full XMMWORD are:

        vxmm1 LABEL XMMWORD
          real4 1.0, 2.0, 3.0, 4.0
        vxmm2 LABEL XMMWORD
          real8 1.0, 2.0

## 3.20 Optional Array Size for LABEL Directive

The LABEL directive accepts an optional array size argument:

    myarray LABEL word : 10 ; myarray is assumed to be an array of 10 words
        dw 1,2,3,4,5,6,7,8,9,10

Please note that the array size argument defines the array's number of elements, not the array's size in bytes.

This extension allows to define large initialized arrays, not restricted by line size limits. The SIZEOF and LENGTHOF operators will return the same values as if the array had been defined via the DUP operator.

The array size argument may be a forward reference:

    myarray LABEL word : size_myarray / sizeof word
        dw 1,2,3,4,5,6,7,8,9,10
    size_myarray equ $ - myarray

## 3.21 Optional Name Argument for Simplified Segment Directives

Masm allows an optional argument for simplified segment directives .CODE, .FARDATA and .FARDATA?. This is to set the name of the segment that is to be opened. JWasm will also accept the name argument for those directives; additionally, it's accepted for .DATA, .DATA? and .CONST directives.

## 3.22 Segment Attribute COMDAT

With segment attribute COMDAT one may define COMDAT sections. A COMDAT section is a section that can be defined by more than one object file. A COMDAT section must contain at least one symbol, the COMDAT symbol. The syntax to define the section is:

        segname SEGMENT COMDAT( selection [, assoc_segment ] ) ...

The selection argument tells the linker what to do if multiple definitions of a COMDAT symbol are found; the accepted values are:

Value |  | Description
1 | no duplicates | If the symbol is already defined, the linker issues a "multiply defined symbol" error.
2 | any | Any section that defines the same COMDAT symbol can be linked; the rest are removed.
3 | same size | The linker chooses an arbitrary section among the definitions for this symbol. If all definitions are not the same size, a "multiply defined symbol" error is issued.
4 | exact match | The linker chooses an arbitrary section among the definitions for this symbol. If all definitions do not match exactly, a "multiply defined symbol" error is issued.
5 | associative | The section is linked if a certain other COMDAT section ( see the assoc_segment in the syntax description ) is linked.
6 | largest | The linker chooses the largest definition from among all of the definitions for this symbol. If multiple definitions have this size, the choice between them is arbitrary.

Currently support for COMDAT is restricted to COFF.

JWasm won't do anything special with COMDAT sections; in future releases this may change: cmdline options similar to the Microsoft VC compiler options -Gf or -Gy may be added.

To create an object module that places each function in its own COMDAT section ( as it is done by MS VC if the -Gy option is given ), it is recommended to use COMDAT in conjunction with ALIAS:

        _TEXT_proc1 segment flat comdat(1) alias(".text")
        proc1 proc c
            ...
        proc1 endp
        _TEXT1_proc1 ends

        _TEXT_proc2 segment flat comdat(1) alias(".text")
        proc2 proc c private
            ...
        proc2 endp
        _TEXT2_proc2 ends

        _TEXT_proc3 segment flat comdat(1) alias(".text")
        proc3 proc c
            ...
        proc3 endp
        _TEXT_proc3 ends

## 3.23 Attribute VARARGML for last Macro Parameter

VARARGML has mostly the same effects as attribute VARARG; the difference is that VARARGML will make the assembler concat lines if the last character on the line is a comma.

## 3.24 Miscellaneous

  3.24.1 Numeric constant __JWASM__
  3.24.2 Operating System Argument for .MODEL
  3.24.3 Accepted Parameters for IF[N]DEF Directive
  3.24.4 Visibility of Procedures
  3.24.5 Non-RIP-Relative Addressing in 64-Bit

### 3.24.1 Numeric constant __JWASM__

__JWASM__ is a predefined symbol, its value is the current JWasm version * 100, that is, for v1.9 the value is 190. The predefined text equate @Version won't contain JWasm's version, for compatibility reasons it has value <800> (since v2.06, previously the value was <615>).

### 3.24.2 Operating System Argument for .MODEL

The .MODEL directive has an optional "operating system" argument. Masm accepts value OS_DOS only, JWasm accepts values OS_DOS and OS_OS2. This setting will affect the generated code of directives .STARTUP and .EXIT for 16-bit memory models.

### 3.24.3 Accepted Parameters for IF[N]DEF Directive

Masm's IF[N]DEF directive accepts user-defined symbols and registers, but fails for instructions, directives and other reserved words. JWasm's IF[N}DEF implementation accepts those symbols as well. OTOH, JWasm is a bit more picky and will display a warning if more than one item is found behind the directive - Masm just takes the first and silently skips the rest.

Also see Member Argument for IF[N]DEF and .ERR[N]DEF Directives.

### 3.24.4 Visibility of Procedures

When a PROTO or EXTERNDEF directive for a symbol is located in a module before a matching PROC directive, the visibility of this Procedure ( "public" vs "private", or "external" vs. "static" ) is handled differently in Masm v6 or 7 and Masm v8 or newer:

Since Masm v8, a PROTO or EXTERNDEF for a symbol which is later defined as a PROC will make the procedure public, no matter what a possible visibility attribute of the PROC itself - or the default one set with OPTION PROC - is telling.

OTOH, with Masm v6/7, both the visibility attribute of the PROC directive and the current default setting of OPTION PROC will affect the symbol's visibility.

                    Masm6 Masm8 JWasm JWasm+Zv8
          -------------------------------------
          On,E,P            x             x
          On,E,Pn           x             x
          On,E,Pp     x     x      x      x
          Op,E,P      x     x      x      x
          Op,E,Pn     x     x             x
          Op,E,Pp     x     x      x      x

          On = OPTION PROC:PRIVATE
          Op = OPTION PROC:PUBLIC
          E  = PROTO or EXTERNDEF before PROC
          P  = PROC without visibility attribute
          Pn = PROC with PRIVATE visibility attribute
          Pp = PROC with PUBLIC visibility attribute
          x  = procedure will be public

As default, JWasm more or less copies the Masm v6/7 behavior. The difference is that an explicite visibility attribute behind PROC has the highest priority for JWasm. However, since v2.04, there's an additional cmdline option -Zv8 which will make JWasm behave like Masm v8+.

It should be noted that without a PROTO/EXTERNDEF before PROC, there are no differences between Masm v6, v8 and JWasm, and the -Zv8 switch also has no effect then.

### 3.24.5 Non-RIP-Relative Addressing in 64-Bit

In 64-bit a RIP-relative addressing mode was introduced. This mode is used as default for direct addressing, because it allows to access all code or data labels with a 32-bit displacement. However, for constant address locations this mode is not appropriate and won't be used:

         mov al, gs:[1000h]
         mov al, gs:[100000000h]

If a constant address is to be accessed without segment prefixes - note that in 64-bit, only segment registers FS and GS can be used as segment prefixes - one has to use the FLAT keyword in JWasm:

         mov al, FLAT:[1000h]           ;invalid for Masm
         mov al, FLAT:[100000000h]      ;invalid for Masm

This syntax differs from Masm's, because Masm won't accept FLAT. In 64-bit Masm, the syntax for accessing constant addresses is instead:

         mov al, [1000h]               ;invalid for JWasm
         mov al, [100000000h]          ;invalid for JWasm

The code that will be generated won't show any differences:

    0000000000000000: 65 8A 04 25 10 00 00 00              mov al,byte ptr gs:[00000010h]
    0000000000000008: 65 A0 00 00 00 00 01 00 00 00        mov al,byte ptr gs:[0000000100000000h]
    0000000000000012: 8A 04 25 10 00 00 00                 mov al,byte ptr ds:[00000010h]
    0000000000000019: A0 00 00 00 00 01 00 00 00           mov al,byte ptr ds:[0000000100000000h]

# 4. Instruction Sets

JWasm supports all instructions sets supported by Masm v8. These are

  - the instructions implemented by 8086, 80186, 80286, 80386, 80486.
  - the Pentium and Pentium Pro instructions.
  - the MMX and K3D instruction set extensions.
  - the SSE, SSE2, SSE3 and SSSE3 instruction set extensions.
  - the Intel VMX instruction set extension ( since JWasm v2.09 ).
  - the x86-64 64-bit instruction set ( implemented by ML64 ).

Additionally supported are

  - SSE4.1 and SSE4.2 instruction sets ( since JWasm v2.01 ).
  - AVX instruction set ( since JWasm v2.06 ).

With Masm, SSE4.1 and SSE4.2 require Masm v9; AVX requires Masm v10.

# 5. Code Generation Differences

JWasm might generate slightly different code than Masm on some occasions. Commandline option -Zg should eliminate most of these differences. However, some differences are due to fixed Masm bugs (see below), in which case option -Zg won't have any effect.

For a few instructions, the encoding differs between Masm versions.

Example:

        cmp al,dl

is encoded `38 D0` in Masm v6, but `3A C2` in Masm v8. In such cases, JWasm will prefer to copy the encoding of Masm v8.

## 5.1 Forward References in Macro Expressions

Like Masm, JWasm usually evaluates expressions in preprocessor directives during the first pass only. However, due to different jump optimization strategies of Masm and JWasm, the results may differ. This is very unlikely to impose a problem, but it is mentioned here for completeness. An example (found in README.TXT of Masm v6.14):

          Label1:
               JMP Label2
          Label2:

          REPEAT Label2 - Label1
               INC AX
          ENDM

Masm will - incorrectly - repeat the loop 10 times, although the result of expression `Label2 - Label1` is 2 only. OTOH, JWasm will repeat the loop 2 times only, because it's using an "optimistic" strategy concerning forward references.

# 6. Output Formats

The format of the assembler's output is selected by commandline options. These are:

-omf | Intel's "relocatable Object Module Format", including 32-bit MS extensions. It's the default.
-coff | (MS) COFF object module format, supports flat memory models only. It's usually used for 32-bit Windows modules.
-elf | 32-Bit ELF ("Executable and Linkable Format") object modules.
-elf64 | 64-bit ELF object modules.
-win64 | 64-bit format for Win64 object modules. COFF variant with 64-bit extensions.
-djgpp | COFF variant used by DJGPP.
-bin | raw binary format.
-mz | DOS MZ binary format.
-pe | 32- and 64-bit PE binaries.

The formats selected by -bin, -mz and -pe are binary formats, hence the output is not supposed to be fed to a linker.

## 6.1 OMF Output Format

The OMF format fully supports the segmented architecture of the x86 cpu. The specification has been extended around 1990 to support 32-bit, including the FLAT memory model. However, since it's a bit old now, there's no support of some of the new relocations introduced for 64-bit.

- OMF won't support the IMAGEREL and SECTIONREL operators.
- JWasm currently won't emit OMF LIDATA records ( unlike Masm). This means that if the assembly source contains lots of arrays defined with DUP, the object module might become significantly larger than a similiar object module written by Masm.
- JWasm emits a few COMENT records that Masm won't. These are remnants of Open Watcom's WASM; they may be suppressed with commandline options -zlc and -zld. They shouldn't do any harm, though.

The OMF object module consists of records of certain types. JWasm writes those records in the following order:

Type |  | Description
--- | --- | ---
THEADR | 1 | Marks the start of an object module, contains the name of the source file.
COMENT, class A1h | 1 | MS extension; tells linker the CodeView version number. Emitted if -Zi option is active.
COMENT, class E9h | n | Borland-style auto-dependency record(s). Emitted if -Zd or -Zi options are active.
COMENT, class 9Eh | 1 | MS extension; directs the linker to use a "standardized" segment ordering. Emitted if the .DOSSEG directive is found in the source.
COMENT, class 9Fh | n | Default library search name(s). Emitted if INCLUDELIB directives are used.
LNAMES | n | Defines names for segments and groups ( optionally also for externals, communals and publics ).
SEGDEF | n | Defines segment(s).
COMENT, class FEh | n | Tells WLink to do FARCALL optimization for a specific segment. Suppressed with -zld.
GRPDEF | n | Defines group(s).
EXTDEF | n | Defines external(s).
COMENT, class A8h | n | Defines weak external(s). Emitted if EXTERN directive is used with "altname".
COMDEF | n | Defines communal(s).
ALIAS | n | Defines alias(es).
PUBDEF | n | Defines public(s).
COMENT, class A0h | n | Defines export(s). Emitted if the EXPORT attribute is used in a PROC directive.
COMENT, class A2h | 1 | Link Pass Separator. Emitted if no entry point is defined in this object module.
LEDATA | n | Data record; defines segment content(s).
FIXUPP | n | Contains information to make the linker resolve references between object modules.
LINNUM | n | Line number information. Emitted if -Zd or -Zi option is active.
COMENT, class FDh | n | Tells disassembler that a code segment contains data. Suppressed with -zlc.
MODEND | 1 | Marks the end of the object module; optionally defines the entry point.

LEDATA, FIXUPP and LINNUM records usually are intermixed; a FIXUPP and/or a LINNUM record appears immediately after the LEDATA record to which it refers.
Since v2.11, multiple THEADR records are written if cmdline options -Zd or -Zi are set and line number information is written for more than one source file; this conforms to MASM behavior.

## 6.2 COFF Output Format

The COFF object module format is suitable for flat, non-segmented memory models. In most cases the COFF format is used for 32-bit code. However, it's possible to create a 64-bit COFF module if the current cpu is .x64 when the .MODEL directive is parsed ( note that -win64 is the usual way to create modules for 64-bit Windows ). To some extent 16-bit code is also supported with COFF, although OMF will always be the better choice then.

- The -safeseh cmdline option and the .SAFESEH directive are supported by COFF only.
- Not supported by COFF are:
  - the GROUP directive
  - the directives to control segment order: .ALPHA, .DOSSEG, .SEQ
  - code that will generate "far" fixups (i.e. direct FAR calls or jumps ).
- A few, common segment names are translated in the output module when COFF is selected:
  - name _TEXT is translated to .text
  - name _DATA is translated to .data
  - name CONST is translated to .rdata
  - name _BSS is translated to .bss
  This also affects simplified segment directives, since _TEXT, _DATA, CONST and _BSS segments are internally generated when directives .CODE, .DATA, .CONST or .DATA? are detected.
- If COFF is selected, Masm will ignore segment combine type STACK and treat stack segments just like normal data segments ( the MS linker and compatibles will set the stack's size with commandline options ). JWasm DOES NOT ignore combine type STACK for the COFF output format; additionally, unless the segment contains initialized data, JWasm will reset the size of stack segments to 0.
- Directive EXTERN name (altname) : <type> will define a weak external with characteristics IMAGE_WEAK_EXTERN_SEARCH_LIBRARY ( see MS PE and COFF specification ).
- Directive ALIAS <aliasname>=<actual name> will define a weak external with characteristics IMAGE_WEAK_EXTERN_SEARCH_ALIAS ( see MS PE and COFF specification ).
- There are some cmdline options to control the extent of symbols that are written to the COFF output module: -zlf, -zlp and -zls.

## 6.3 Win64 Output Format

### 6.3.1 Win64 Basics

This output format, that is selected with the -win64 commandline option, is a variant of the COFF output format. It's commonly used to create object modules for 64-bit Windows. The default calling convention is the Win64 FASTCALL implementation.

### 6.3.2 Directive INVOKE in Win64

Unlike the 64-bit version of Masm, which doesn't support INVOKE anymore, JWasm still does; however, please be aware of some peculiarities:

- in theory, using INVOKE requires the FRAME attribute for PROC. It will work without FRAME, but Win64 SEH won't be happy with it then.
- the default implementation in 64-bit is very simple: for each INVOKE register RSP is reduced by the space required for the arguments, then the call is issued and finally register RSP is restored. To enable a more efficient code generation see OPTION WIN64, INVOKE Stack Space Reservation - this option is not active as default because it virtually requires a certain programming style.
- there is no additional check that the stack is aligned to 16 byte. The PROC's FRAME attribute ensures that the stack is correctly aligned after the prologue is done. However, it's the programmers responsibility that the stack is still aligned when the code generated by INVOKE starts.
- parameter names listed behind the PROC directive will always refer to the parameter's shadow space on the stack. However, on a procedure's entry the actual values of the first four parameters are hold in registers, and the value of the associated shadow spaces are undefined. See OPTION WIN64, Store Register Arguments, how to make JWasm automatically save the register arguments and thus initialize the shadow space on a procedure's entry.

### 6.3.3 Win64 Structured Exception Handling (SEH)

SEH in Win64 differs significantly from the implementation in Win32. It's very well possible to ignore Win64 SEH for assembly. However, if an assembly routine wants to comply to these rules, a thorough understanding of the Win64 ABI is necessary. Masm ( the 64-bit version ) supplies some "primitives" for SEH support (.ALLOCSTACK, .PUSHREG, .SAVEREG, ...), along with a new FRAME attribute for the PROC directive. These features are also supported by JWasm. See sample Win64_3 how the "primitives" are to be used for SEH support.

The big disadvantage is that using the FRAME keyword in Masm "disables" most of the other high level features combined with PROC (function parameters, locals and registers saved with USES) because no function prologues and epilogues are generated anymore. Additionally, the implementation at least in Masm v8 seems to be a bit buggy, at least in Masm v8. Because of this and to ease the usage of SEH in Win64 there is a new directive implemented in JWasm:

            OPTION FRAME:AUTO

If this option is set, JWasm will create Win64 SEH-compatible prologues and epilogues. If the option is off, JWasm will behave Masm-compatible, that is, FRAME found in a PROC directive will disable automatic prologue/epilogue generation. See sample Win64_3e how this option is supposed to be used.

As for the PROC syntax: The Masm documentation states that FRAME can be used in combination with USES and procedure parameters and must be located behind all parameters. However, this syntax isn't accepted by any Masm version. The only syntax which Masm will accept without being confused is FRAME as the one and only parameter for PROC. Therefore JWasm doesn't follow the Masm documentation in this point: the optional FRAME keyword is expected *before* the procedure parameters. The syntax in JWasm is:

        procname PROC [public] FRAME[:exc_handler] [USES <reglist>] [parameters]

The SEH "primitives" will generate some additional data in segments .pdata and .xdata. This data is somewhat hidden, but JWasm will display the corresponding data definitions in the listing if option -Sg is set.

Finally, JWasm's default behavior of INVOKE isn't fully SEH-compatible, because the stack pointer is temporarily changed to make room for arguments. To make INVOKE comply to SEH, OPTION WIN64 INVOKE Stack Space Reservation has to be used.

## 6.4 Binary Output Format

If the binary output format has been selected, the contents of the file are just the raw data bytes emitted by the assembler, no header, relocations or symbol tables are generated. All references have to be resolved internally.

The binary format is most useful for bootloaders or DOS COM files, but may be used to create any binary format. See sample Win32_5, that demonstrates how the binary format is used to create a Win32 application.

If a listing file is produced, a binary map will be added, which shows the file and memory layout of the image:

                                        .model tiny

                                        .data

    00000000  0D0A48656C6C6F2C20    str1    db 13,10,"Hello, world!",13,10,'$'

    00000000                            .code

                                        org 100h

    00000100                        start:

    00000100  B409                      mov ah, 09h
    00000102  BA0000                    mov dx, offset str1
    00000105  CD21                      int 21h
    00000107  B8004C                    mov ax, 4c00h
    0000010A  CD21                      int 21h

                                        end start

    Binary Map:

    Segment                  Pos(file)      VA  Size(fil) Size(mem)
    ---------------------------------------------------------------
    _TEXT                           0      100         C         C
    _DATA                           C      10C        12        12
    ---------------------------------------------------------------
                                                      1E        1E

Note that bytes with "undefined contents" at the start and the end of the output file are skipped and won't become part of the binary.

## 6.5 PE Output Format

The ( Windows ) PE output format ( both 32- and 64-bit ) is a binary format - there's no link step supposed to follow the assembly step. Hence all references must be resolved internally, no external references are possible. Since the Windows ABI is implemented as a set of dlls that export function names, it's necessary to provide a mechanism to call such external functions - in the PE format this is achieved with the help of directive OPTION DLLIMPORT; it allows to attach a module name to function prototypes used by the assembly source and consequently give the assembler the means to resolve all references without the help of a linker.

The PE format requires a .MODEL FLAT directive in the source code. This directive will trigger the creation of the internal PE-header section, the value of the cpu at this time will determine whether a 32- or 64-bit PE binary is to be written.

As in all binary formats, the listing will contain a binary map; see Binary Output Format for more details.

If -pe is set, a few sections will be created internally:

  -.hdr$1 : section will contain the DOS MZ-stub.
  -.hdr$2 : section will contain the PE header
  -.hdr$3 : section will contain the PE object table

The default values in the PE header are

Field | 32-bit Value | 64-bit Value (if different)
--- | --- | ---
Signature | "PE" |
Machine | 14Ch | 8664h
Timestamp | date & time |
Size OptionalHeader | 0E0h | 0F0h
Characteristics | 10Fh | 12Fh
Magic | 10Bh | 20Bh
LinkerVersion | 5.1 |
ImageBase | exe: 400000h dll: 10000000h | 140000000h 180000000h
SectionAlignment | 1000h |
FileAlignment | 200h |
OSVersion | 4.0 |
ImageVersion | 0.0 |
SubsystemVersion | 4.0 |
Win32Version | 0 |
Checksum | 0 |
Subsystem | 3 (=Console) |
DllCharacteristics | 0 |
SizeOfStack | 100000h,1000h |
SizeOfHeap | 100000h,1000h |
LoaderFlags | 0 |

To change the default values in the PE header there are two options. First, a predefined assembly-time variable @pe_file_flags will map the value of field Characteristics - changing the value of @pe_file_flags will also change the value in the header field. The other fields in the PE header are only accessible by setting the appropriate values in section .hdr$2. Fields not listed in the table above are set internally by the assembler to ensure data integrity and cannot be modified from within the assembly source.

If the PE binary is to use resources, a .rsrc section has to be created which is to contain them. Defining the resources manually works and is doable, but it might become tedious if a lot of resource items are to be defined. Therefore tool res2inc is supplied, which allows to convert a compiled resource file (.RES) to an assembly include file.

If a dll is created with -pe, one has to mark all procedures that are to be exported with the EXPORT attribute. If the exported names are to be undecorated, use the -zze cmdline option.

Sample Win64_8 shows how a 64-bit Windows binary is created with -pe. It also shows how to define resources in .rsrc manually and how to modify default values of PE header fields.

To import functions by number with option -pe, the alias directive has to be used:

        OPTION DLLIMPORT: <kernel32.dll>
        VxDCall1 proto stdcall :dword
        ALIAS <kernel32.1> = <VxDCall1>

# 7. Masm bugs fixed in JWasm

# | Description | Fixed Masm Version
--- | --- | ---
1 | the infamous "invoke" bug: if an argument for invoke has to be expanded (from BYTE or WORD to DWORD, for example ), bad code was generated. | 9
2 | PROTOs contained twice in the source caused an EXTDEF entry to be generated in the object module. | -
3 | "TYPE xmm0" will return 10 in Masm v6 and v7 - the correct value is 16. | 8
4 | a nested structure might cause a GPF in Masm if the embedded STRUCT's starting offset has to be adjusted due to alignment. | -
5 | defining huge arrays in Masm is very slow and might even cause a deadlock if COFF has been selected as output format. | -
6 | for Masm v6 and v7, if an array > 64 kB is defined and output format OMF is selected, the array's size will be mod 0x10000 only. | 8
7 | Masm doesn't flag invalid numbers in struct/array initializer strings. | -
8 | if an ALIAS is defined somewhere in the source and the symbol table is listed, a 'General Failure' error occurs in Masm if output format is OMF. | -
9 | Type "coerces" for DWORD data items defined in a 32bit segment are ignored by Masm, i.e., "dd far16 ptr <symbol>" will generate a near32 fixup instead of a far16 one. | -
10 | if the ALIGN directive has to add 5 bytes in 32bit code segments, Masm includes an "add eax,0" opcode, which isn't a no-op because flags are modified. | -
11 | silent truncation of immediate constants: Masm v6 and v7 will accept line "mov [word_variable],12345h" without error. | 8
12 | preprocessed output with option -EP may erroneously contain text macros and macro function calls if the macros are located in the initialization string of a structured variable. | -
13 | Masm generates wrong code if a conditional jump is coupled with a type coercion which modifies offset magnitude. Examples: "jz near32 ptr ..." in 16bit code or "jz near16 ptr ..." in 32bit code). | -
14 | if the arguments given to Masm end with an option which expects a parameter (i.e. "ml -c -Fo"), a 'General Failure' may occur. | -
15 | floating-point data items in Masm can be followed by any suffix (example: REAL4 1.0foo, 2.0bar). JWasm won't accept this. | -
16 | If a local is defined inside a macro, Masm will create a unique name for it. The name is constructed by using '??' as prefix, followed by a hexadecimal number with 4 digits. There is no check for overflow, however, so if the total of locals in all macros exceeds 65536, strange errors will occur. | -
17 | If a weak external is defined for -coff with the ALIAS directive, an invalid fixup - and also a strange entry in the module's symbol table - is created. | -
18 | If a section contains more than 0xffff relocations in COFF, the number of relocations that is stored in the object module is just the value of the lower 16-bit half of the relocation count. | 8
19 | If a symbolic constant (=equate) is made public in OMF format, Masm will store the symbol's value in a 16-bit record if it is in the range -32768 ... 65535. If the symbol is referenced in another module as a 32-bit number, it is always zero-extended, never sign-extended; hence values -1 ... -32768 will become 65535 ... 32768. | -
20 | if data labels become public by the -Zf option ( and not by the PUBLIC directive ), their names are not decorated. Also, if format is COFF, they won't become true publics, they're just included in the symbol table with class "static". | -
21 | in 16-bit code, Masm will accept opcode "mov ax,es:[10000h]" although offset 10000h exceeds 16-bit ( it will be truncated to 16-bit ). JWasm emits a level 3 warning and the offset is NOT truncated. | -

It's slightly dangerous to fix old Masm bugs, since some code might work only if the bugs exists. So no, JWasm won't achieve 100% Masm compatibility.

# 8. Optional Features

There exist some features that are not activated in the precompiled binaries. To enable these options, the JWasm source must be recompiled with one or more switches set in the command line:

## Support for Assembly Source generated by Intel C++ compiler

This option is enabled with switch -DDOTNAMEX. It will make the assembler accept names that contain dots if the name starts with a dot or an underscore. Note that this behavior is not compatible with standard Masm syntax.

# 9. Known Bugs and missing Features

## a) Bugs which are known but not fixed yet:

There are currently no known bugs.

## b) Features which aren't implemented yet:

  - directives PAGE, TITLE, SUBTITLE, SUBTTL. the directives are ignored and a warning (level 4) is displayed.
  - the following parameters of the OPTION directive:
    - OLDMACROS
    - EXPR16
    - READONLY
  - optional parameter NONUNIQUE for structures is ignored.
  - commandline option -AT (Enable tiny model).
  - commandline options -Sp, -Ss and -St (set page length, subtitle and title).
  - commandline option -H (set max external name length).
  - commandline option -Ta (Assemble non-.ASM file).
  - commandline option -Zd for ELF output format.
  - commandline option -Zi for ELF output format.

If there's ever a problem with one of the missing features, it's very likely that it's related to OPTION OLDMACROS. This option makes Masm 6 emulate two Masm 5.1 peculiarities:

  - macro arguments may be separated by spaces
  - ampersands (&) inside the macro must match the current level of macro nesting.

## c) Missing features which most likely won't be implemented:

  - syntax "mm(n)" and "xmm(n)" (supported by Masm v6 and v7 only)
  - commandline option -Bl, -F, -Fe, -Fm and -link: since JWasm doesn't launch a linker, those options are useless.
  - commandline options -Fr and -FR (generate browser info).
  - commandline option -Sc (generate timings in listing).
  - commandline option -errorReport (Report internal assembler errors to Microsoft).

# 10. License

This manual was written by Andreas Grech ( aka Japheth ).

It may be redistributed as long as it is free of charge.

# Appendix A. JWasm Reserved Words

Reserved Words are case-insensitive. Besides the items listed below all instruction mnemonics are also Reserved Words.

## Registers 16- and 32-bit Modes

8-bit registers | AL | CL | DL | BL | AH | CH | DH | BH
16-bit registers | AX | CX | DX | BX | SP | BP | SI | DI
32-bit registers | EAX | ECX | EDX | EBX | ESP | EBP | ESI | EDI
Segment registers | ES | CS | SS | DS | FS | GS |  |
Floating-point registers | ST | ST(1) | ST(2) | ST(3) | ST(4) | ST(5) | ST(6) | ST(7)
MMX registers | MM0 | MM1 | MM2 | MM3 | MM4 | MM5 | MM6 | MM7
SSE registers | XMM0 | XMM1 | XMM2 | XMM3 | XMM4 | XMM5 | XMM6 | XMM7
AVX registers | YMM0 | YMM1 | YMM2 | YMM3 | YMM4 | YMM5 | YMM6 | YMM7
Control registers | CR0 |  | CR2 | CR3 | CR4 |  |  |
Debug registers | DR0 | DR1 | DR2 | DR3 |  |  | DR6 | DR7
Test registers[1] |  |  |  | TR3 | TR4 | TR5 | TR6 | TR7

[1]: invalid in 64-bit mode.

## Additional Registers in 64-bit Mode

8-bit registers |  |  |  |  | SPL | BPL | SIL | DIL
| R8B | R9B | R10B | R11B | R12B | R13B | R14B | R15B
16-bit registers | R8W | R9W | R10W | R11W | R12W | R13W | R14W | R15W
32-bit registers | R8D | R9D | R10D | R11D | R12D | R13D | R14D | R15D
64-bit registers | RAX | RCX | RDX | RBX | RSP | RBP | RSI | RDI
| R8 | R9 | R10 | R11 | R12 | R13 | R14 | R15
SSE registers | XMM8 | XMM9 | XMM10 | XMM11 | XMM12 | XMM13 | XMM14 | XMM15
AVX registers | YMM8 | YMM9 | YMM10 | YMM11 | YMM12 | YMM13 | YMM14 | YMM15
Control registers | CR8 |  |  |  |  |  |  |

## Types

BYTE
SBYTE
WORD
SWORD
DWORD
SDWORD
REAL4
FWORD
QWORD
SQWORD
REAL8
TBYTE
REAL10
OWORD
YMMWORD
NEAR
FAR
NEAR16
NEAR32
FAR16
FAR32
MMWORD
XMMWORD

## Unary Operators

.TYPE
HIGH
HIGH32
HIGHWORD
IMAGEREL[1]
LENGTH
LENGTHOF
LOW
LOW32
LOWWORD
LROFFSET
MASK
OFFSET
OPATTR
SECTIONREL[1]
SEG
SHORT
SIZE
SIZEOF
THIS
TYPE
WIDTH

[1]: not for OMF output format.

## Binary Operators

EQ
NE
GE
GT
LE
LT
MOD
PTR
DUP
SHL[1]
SHR[1]
AND[1]
OR[1]
XOR[1]

[1]: these keywords are also instructions.

## Directives

.8086
.186
.286
.286C
.286P
.386
.386C
.386P
.486
.486P
.586
.586P
.686
.686P
.K3D
.MMX
.XMM
.X64
.X64P
.8087
.287
.387
.NO87
.CREF
.LIST
.LISTALL
.LISTIF, .LFCOND
.NOCREF, .XCREF
.NOLIST, .XLIST
.NOLISTIF, .SFCOND
.TFCOND
PAGE
SUBTITLE, SUBTTL
TITLE
.LISTMACRO, .XALL
.LISTMACROALL, .LALL
.NOLISTMACRO, .SALL
.ALPHA
.DOSSEG, DOSSEG
.SEQ
.CODE
.STACK
.DATA
.DATA?
.FARDATA
.FARDATA?
.CONST
.IF
.REPEAT
.WHILE
.BREAK
.CONTINUE
.ELSE
.ELSEIF
.ENDIF
.ENDW
.UNTIL
.UNTILCXZ
.EXIT
.STARTUP
.MODEL
.RADIX
.SAFESEH
.ERR
.ERR1
.ERR2
.ERRE
.ERRNZ
.ERRDIF
.ERRDIFI
.ERRIDN
.ERRIDNI
.ERRB
.ERRNB
.ERRDEF
.ERRNDEF
COMMENT
IF
IFE
IF1
IF2
IFDIF
IFDIFI
IFIDN
IFIDNI
IFB
IFNB
IFDEF
IFNDEF
ELSE
ELSEIF
ELSEIFE
ELSEIF1
ELSEIF2
ELSEIFDIF
ELSEIFDIFI
ELSEIFIDN
ELSEIFIDNI
ELSEIFB
ELSEIFNB
ELSEIFDEF
ELSEIFNDEF
ENDIF
FOR, IRP
FORC, IRPC
REPEAT, REPT
WHILE
MACRO
EXITM
ENDM
GOTO
PURGE
INCLUDE
TEXTEQU
CATSTR
SUBSTR
INSTR
SIZESTR
DB
DW
DD
DF
DQ
DT
STRUCT, STRUC
UNION
TYPEDEF
RECORD
COMM
EXTERN, EXTRN
EXTERNDEF
PUBLIC
PROTO
PROC
ENDP
LOCAL
LABEL
INVOKE
ORG
ALIGN
EVEN
SEGMENT
ENDS
GROUP
ASSUME
ALIAS
ECHO, %OUT
END
EQU
INCBIN
INCLUDELIB
NAME
OPTION
POPCONTEXT
PUSHCONTEXT

## Additional Directives in 64-bit Mode

.ALLOCSTACK
.ENDPROLOG
.PUSHFRAME
.PUSHREG
.SAVEREG
.SAVEXMM128
.SETFRAME

## Other Reserved Words

ADDR
FLAT
VARARG
FRAME[1]
C
SYSCALL[2]
STDCALL
PASCAL
FORTRAN
BASIC
FASTCALL

[1]: in 64-bit mode only.
[2]: in 64-bit, calling convention SYSCALL is renamed to SYSCALL_, since in this mode there exists a SYSCALL instruction.

# Appendix B. Source Samples

  Win64_3 - SEH Support in Win64
  Win64_3e - SEH Support in Win64 (JWasm specific)
  DOS64 - Switch to Long Mode and Back
  Win32_5 - Create a Win32 Binary with -bin
  Win32_7 - Usage of OPTION DLLIMPORT and -Fd Switch
  Win64_8 - Create a Win64 Binary with -pe

## Win64_3 - SEH Support in Win64

    ;--- This sample shows how to use SEH primitives. It doesn't use hll
    ;--- directives. Thus this source can be assembled by both JWasm
    ;--- and Masm64.
    ;---
    ;--- to assemble enter:
    ;---   JWasm -win64 Win64_3.asm
    ;--- or:
    ;---   ml64 -c Win64_3.asm
    ;---
    ;--- to link the binary enter:
    ;---   Link Win64_3.obj

        option casemap:none

        includelib kernel32.lib
        includelib user32.lib

    HINSTANCE typedef QWORD
    HWND      typedef QWORD
    HMENU     typedef QWORD
    HICON     typedef QWORD
    HBRUSH    typedef QWORD
    HCURSOR   typedef QWORD
    WPARAM    typedef QWORD
    LPARAM    typedef QWORD
    LPSTR     typedef QWORD
    LPVOID    typedef QWORD
    UINT      typedef DWORD

    NULL           equ 0
    WS_OVERLAPPEDWINDOW equ 0CF0000h
    CW_USEDEFAULT  equ 80000000h
    SW_SHOWDEFAULT equ 10
    SW_SHOWNORMAL  equ 1
    IDC_ARROW      equ 32512
    IDI_APPLICATION equ 32512
    WM_DESTROY     equ 2
    CS_VREDRAW     equ 1
    CS_HREDRAW     equ 2
    COLOR_WINDOW   equ 5

    proto_WNDPROC typedef proto :HWND,:QWORD,:WPARAM,:LPARAM
    WNDPROC typedef ptr proto_WNDPROC

    WNDCLASSEXA struct 8
    cbSize          DWORD   ?
    style           DWORD   ?
    lpfnWndProc     WNDPROC ?
    cbClsExtra      DWORD   ?
    cbWndExtra      DWORD   ?
    hInstance       HINSTANCE ?
    hIcon           HICON   ?
    hCursor         HCURSOR ?
    hbrBackground   HBRUSH  ?
    lpszMenuName    LPSTR   ?
    lpszClassName   LPSTR   ?
    hIconSm         HICON   ?
    WNDCLASSEXA ends

    POINT   struct
    x   SDWORD  ?
    y   SDWORD  ?
    POINT   ends

    MSG struct 8
    hwnd    HWND    ?
    message DWORD   ?
    wParam  WPARAM  ?
    lParam  LPARAM  ?
    time    DWORD   ?
    pt      POINT   <>
    MSG ends

    GetModuleHandleA proto :LPSTR
    GetCommandLineA  proto
    ExitProcess      proto :UINT
    LoadIconA        proto :HINSTANCE, :LPSTR
    LoadCursorA      proto :HINSTANCE, :LPSTR
    RegisterClassExA proto :ptr WNDCLASSEXA
    CreateWindowExA  proto :DWORD, :LPSTR, :LPSTR, :DWORD, :SDWORD, :SDWORD, :SDWORD, :SDWORD, :HWND, :HMENU, :HINSTANCE, :LPVOID
    ShowWindow       proto :HWND, :SDWORD
    UpdateWindow     proto :HWND
    GetMessageA      proto :ptr MSG, :HWND, :SDWORD, :SDWORD
    TranslateMessage proto :ptr MSG
    DispatchMessageA proto :ptr MSG
    PostQuitMessage  proto :SDWORD
    DefWindowProcA   proto :HWND, :UINT, :WPARAM, :LPARAM

    ;WinMain proto :HINSTANCE, :HINSTANCE, :LPSTR, :UINT

        .data

    ClassName db "SimpleWinClass",0
    AppName  db "Our First Window",0

        .data?

    hInstance HINSTANCE ?
    CommandLine LPSTR ?

        .code

    WinMainCRTStartup proc FRAME
        push   rbp
        .pushreg rbp
        mov    rbp,rsp
        .setframe rbp, 0
        .endprolog

        sub    rsp,32
        mov    ecx,NULL
        call   GetModuleHandleA
        mov    hInstance, rax
        call   GetCommandLineA
        mov    CommandLine, rax
        mov    rcx, hInstance
        mov    rdx, NULL
        mov    r8, CommandLine
        mov    r9d, SW_SHOWDEFAULT
        call   WinMain
        mov    ecx, eax
        call   ExitProcess
        align 4
    WinMainCRTStartup endp

    WinMain proc FRAME

        push  rbp
        .pushreg rbp
        mov   rbp,rsp
        .setframe rbp, 0
        .endprolog
        sub   rsp, sizeof WNDCLASSEXA + sizeof MSG + sizeof HWND + 12*8

    hInst     equ <[rbp+10h]>
    hPrevInst equ <[rbp+18h]>
    CmdLine   equ <[rbp+20h]>
    CmdShow   equ <[rbp+28h]>

    wc   equ <[rbp - sizeof WNDCLASSEXA].WNDCLASSEXA>
    msg  equ <[rbp - sizeof WNDCLASSEXA - sizeof MSG].MSG>
    hwnd equ <[rbp - sizeof WNDCLASSEXA - sizeof MSG - sizeof HWND]>

        mov   hInst, rcx  ;store param1 in shadow space

        mov   wc.cbSize, SIZEOF WNDCLASSEXA
        mov   wc.style, CS_HREDRAW or CS_VREDRAW
    ;   mov   rax, OFFSET WndProc  ;using LEA is preferable
        lea   rax, [WndProc]
        mov   wc.lpfnWndProc, rax
        mov   wc.cbClsExtra, NULL
        mov   wc.cbWndExtra, NULL
        mov   wc.hInstance, rcx
        mov   wc.hbrBackground, COLOR_WINDOW+1
        mov   wc.lpszMenuName, NULL
    ;    mov   rax, OFFSET ClassName  ;using LEA is preferable
        lea   rax, [ClassName]
        mov   wc.lpszClassName, rax
        mov   ecx, NULL
        mov   edx, IDI_APPLICATION
        call  LoadIconA
        mov   wc.hIcon, rax
        mov   wc.hIconSm, rax
        mov   ecx, NULL
        mov   edx, IDC_ARROW
        call  LoadCursorA
        mov   wc.hCursor,rax
        lea   rcx, wc
        call  RegisterClassExA
        mov   ecx, NULL
        lea   rdx, [ClassName]
        lea   r8, [AppName]
        mov   r9d, WS_OVERLAPPEDWINDOW
        mov   dword ptr [rsp+4*8], CW_USEDEFAULT
        mov   dword ptr [rsp+5*8], CW_USEDEFAULT
        mov   dword ptr [rsp+6*8], CW_USEDEFAULT
        mov   dword ptr [rsp+7*8], CW_USEDEFAULT
        mov   qword ptr [rsp+8*8], NULL
        mov   qword ptr [rsp+9*8], NULL
        mov   rax, hInst
        mov   [rsp+10*8], rax
        mov   qword ptr [rsp+11*8], NULL
        call  CreateWindowExA
        mov   hwnd,rax
        mov   rcx, hwnd
        mov   edx, SW_SHOWNORMAL
        call  ShowWindow
        mov   rcx, hwnd
        call  UpdateWindow
    ;--- message loop
    @@:
            lea rcx, msg
            mov rdx, NULL
            mov r8, 0
            mov r9, 0
            call GetMessageA
            and rax, rax
            jz @F
            lea rcx, msg
            call TranslateMessage
            lea rcx, msg
            call DispatchMessageA
            jmp @B
    @@:
        mov   rax, msg.wParam
        add   rsp, sizeof WNDCLASSEXA + sizeof MSG + sizeof HWND + 12*8
        pop   rbp
        ret
        align 4
    WinMain endp

    WndProc proc FRAME

        sub   rsp, 4*8
        .allocstack 4*8
        .endprolog

        cmp edx, WM_DESTROY
        jnz @F
        mov ecx, NULL
        call PostQuitMessage
        xor rax,rax
        jmp exit
    @@:
        call DefWindowProcA
    exit:
        add rsp, 4*8
        ret
        align 4
    WndProc endp

    end

## Win64_3e - SEH Support in Win64 (JWasm specific)

    ;--- SEH support in Win64. Unlike Win64_3,
    ;--- this version uses hll directives, so it cannot be assembled
    ;--- with Masm64. Also, OPTION FRAME:AUTO is used.
    ;---
    ;--- to create the binary enter:
    ;---   JWasm -win64 Win64_3e.asm
    ;---   Link Win64_3e.obj

        option casemap:none
        option frame:auto    ;generate SEH-compatible prologues and epilogues

        includelib kernel32.lib
        includelib user32.lib

    HINSTANCE typedef QWORD
    HWND      typedef QWORD
    HMENU     typedef QWORD
    HICON     typedef QWORD
    HBRUSH    typedef QWORD
    HCURSOR   typedef QWORD
    WPARAM    typedef QWORD
    LPARAM    typedef QWORD
    LPSTR     typedef QWORD
    LPVOID    typedef QWORD
    UINT      typedef DWORD

    NULL           equ 0
    WS_OVERLAPPEDWINDOW equ 0CF0000h
    CW_USEDEFAULT  equ 80000000h
    SW_SHOWDEFAULT equ 10
    SW_SHOWNORMAL  equ 1
    IDC_ARROW      equ 32512
    IDI_APPLICATION equ 32512
    WM_DESTROY     equ 2
    CS_VREDRAW     equ 1
    CS_HREDRAW     equ 2
    COLOR_WINDOW   equ 5

    proto_WNDPROC typedef proto :HWND,:QWORD,:WPARAM,:LPARAM
    WNDPROC typedef ptr proto_WNDPROC

    WNDCLASSEXA struct 8
    cbSize          DWORD   ?
    style           DWORD   ?
    lpfnWndProc     WNDPROC ?
    cbClsExtra      DWORD   ?
    cbWndExtra      DWORD   ?
    hInstance       HINSTANCE ?
    hIcon           HICON   ?
    hCursor         HCURSOR ?
    hbrBackground   HBRUSH  ?
    lpszMenuName    LPSTR   ?
    lpszClassName   LPSTR   ?
    hIconSm         HICON   ?
    WNDCLASSEXA ends

    POINT   struct
    x   SDWORD  ?
    y   SDWORD  ?
    POINT   ends

    MSG struct 8
    hwnd    HWND    ?
    message DWORD   ?
    wParam  WPARAM  ?
    lParam  LPARAM  ?
    time    DWORD   ?
    pt      POINT   <>
    MSG ends

    GetModuleHandleA proto :LPSTR
    GetCommandLineA  proto
    ExitProcess      proto :UINT
    LoadIconA        proto :HINSTANCE, :LPSTR
    LoadCursorA      proto :HINSTANCE, :LPSTR
    RegisterClassExA proto :ptr WNDCLASSEXA
    CreateWindowExA  proto :DWORD, :LPSTR, :LPSTR, :DWORD, :SDWORD, :SDWORD, :SDWORD, :SDWORD, :HWND, :HMENU, :HINSTANCE, :LPVOID
    ShowWindow       proto :HWND, :SDWORD
    UpdateWindow     proto :HWND
    GetMessageA      proto :ptr MSG, :HWND, :SDWORD, :SDWORD
    TranslateMessage proto :ptr MSG
    DispatchMessageA proto :ptr MSG
    PostQuitMessage  proto :SDWORD
    DefWindowProcA   proto :HWND, :UINT, :WPARAM, :LPARAM

    WinMain proto :HINSTANCE, :HINSTANCE, :LPSTR, :UINT

        .data

    ClassName db "SimpleWinClass",0
    AppName  db "Our First Window",0

        .data?

    hInstance HINSTANCE ?
    CommandLine LPSTR ?

        .code

    WinMainCRTStartup proc FRAME

        invoke GetModuleHandleA, NULL
        mov    hInstance, rax
        invoke GetCommandLineA
        mov    CommandLine, rax
        invoke WinMain, hInstance, NULL, CommandLine, SW_SHOWDEFAULT
        invoke ExitProcess, eax

    WinMainCRTStartup endp

    WinMain proc FRAME hInst:HINSTANCE, hPrevInst:HINSTANCE, CmdLine:LPSTR, CmdShow:UINT

        local wc:WNDCLASSEXA
        local msg:MSG
        local hwnd:HWND

        mov   hInst, rcx
        mov   wc.cbSize, SIZEOF WNDCLASSEXA
        mov   wc.style, CS_HREDRAW or CS_VREDRAW
        lea   rax, [WndProc]
        mov   wc.lpfnWndProc, rax
        mov   wc.cbClsExtra, NULL
        mov   wc.cbWndExtra, NULL
        mov   wc.hInstance, rcx
        mov   wc.hbrBackground, COLOR_WINDOW+1
        mov   wc.lpszMenuName, NULL
        lea   rax, [ClassName]
        mov   wc.lpszClassName, rax
        invoke LoadIconA, NULL, IDI_APPLICATION
        mov   wc.hIcon, rax
        mov   wc.hIconSm, rax
        invoke LoadCursorA, NULL, IDC_ARROW
        mov   wc.hCursor,rax
        invoke RegisterClassExA, addr wc
        invoke CreateWindowExA, NULL, ADDR ClassName, ADDR AppName,\
               WS_OVERLAPPEDWINDOW, CW_USEDEFAULT,\
               CW_USEDEFAULT, CW_USEDEFAULT,CW_USEDEFAULT, NULL, NULL,\
               hInst, NULL
        mov   hwnd,rax
        invoke ShowWindow, hwnd, SW_SHOWNORMAL
        invoke UpdateWindow, hwnd
        .while (1)
            invoke GetMessageA, ADDR msg, NULL, 0, 0
            .break .if (!rax)
            invoke TranslateMessage, ADDR msg
            invoke DispatchMessageA, ADDR msg
        .endw
        mov   rax, msg.wParam
        ret
    WinMain endp

    WndProc proc FRAME hWnd:HWND, uMsg:UINT, wParam:WPARAM, lParam:LPARAM

        .if ( edx == WM_DESTROY )
            invoke PostQuitMessage, NULL
            xor rax,rax
        .else
            invoke DefWindowProcA, rcx, edx, r8, r9
        .endif
        ret
    WndProc endp

    end WinMainCRTStartup

## DOS64 - Switch to Long Mode and Back

    ;--- DOS program which switches to long-mode and back.
    ;--- Note: requires at least JWasm v2.
    ;--- Also: needs a 64bit cpu in real-mode to run.
    ;--- Parts of the source are based on samples supplied by
    ;--- sinsi and Tomasz Grysztar in the FASM forum.
    ;--- To create the binary enter:
    ;---  JWasm -mz DOS64.asm

        .x64p

    ;--- 16bit start/exit code

    _TEXT16 segment use16 para public 'CODE'

        assume ds:_TEXT16
        assume es:_TEXT16

    GDTR label fword        ; Global Descriptors Table Register
        dw 4*8-1            ; limit of GDT (size minus one)
        dd offset GDT       ; linear address of GDT
    IDTR label fword        ; Interrupt Descriptor Table Register
        dw 256*16-1         ; limit of IDT (size minus one)
        dd 0                ; linear address of IDT
    nullidt label fword
        dw 3FFh
        dd 0

        align 8
    GDT dq 0                    ; null descriptor
        dw 0FFFFh,0,9A00h,0AFh  ; 64-bit code descriptor
        dw 0FFFFh,0,9A00h,000h  ; compatibility mode code descriptor
        dw 0FFFFh,0,9200h,000h  ; compatibility mode data descriptor

    wPICMask dw 0   ; variable to save/restore PIC masks

    start16:
        push cs
        pop ds
        mov ax,cs
        movzx eax,ax
        shl eax,4
        add dword ptr [GDTR+2], eax ; convert offset to linear address
        mov word ptr [GDT+2*8+2], ax
        mov word ptr [GDT+3*8+2], ax
        shr eax,16
        mov byte ptr [GDT+2*8+4], al
        mov byte ptr [GDT+3*8+4], al

        mov ax,ss
        mov dx,es
        sub ax,dx
        mov bx,sp
        shr bx,4
        add bx,ax
        mov ah,4Ah
        int 21h         ; free unused memory
        push cs
        pop es
        mov ax,ss
        mov dx,cs
        sub ax,dx
        shl ax,4
        add ax,sp
        push ds
        pop ss
        mov sp,ax       ; make a TINY model, CS=SS=DS=ES

        smsw ax
        test al,1
        jz @F
        mov dx,offset err1
        mov ah,9
        int 21h
        mov ah,4Ch
        int 21h
    err1 db "Mode is V86. Need REAL mode to switch to LONG mode!",13,10,'$'
    @@:
        xor edx,edx
        mov eax,80000001h   ; test if long-mode is supported
        cpuid
        test edx,20000000h
        jnz @F
        mov dx,offset err2
        mov ah,9
        int 21h
        mov ah,4Ch
        int 21h
    err2 db "No 64bit cpu detected.",13,10,'$'
    @@:
        mov bx,1000h
        mov ah,48h
        int 21h
        jnc @F
        mov dx,offset err3
        mov ah,9
        int 21h
        mov ah,4Ch
        int 21h
    err3 db "Out of memory",13,10,'$'
    @@:
        add ax,100h-1   ; align to page boundary
        mov al,0
        mov es,ax

    ;--- setup page directories and tables

        sub di,di
        mov cx,4096
        sub eax,eax
        rep stosd       ; clear 4 pages

        sub di,di
        mov ax,es
        movzx eax,ax
        shl eax,4
        mov cr3,eax             ; load page-map level-4 base

        lea edx, [eax+5000h]
        mov dword ptr [IDTR+2], edx

        or eax,111b
        add eax, 1000h
        mov es:[di+0000h],eax   ; first PDP table
        add eax, 1000h
        mov es:[di+1000h],eax   ; first page directory
        add eax, 1000h
        mov es:[di+2000h],eax   ; first page table
        mov di,3000h            ; address of first page table
        mov eax,0 + 111b
        mov cx,256              ; number of pages to map (1 MB)
    @@:
        stosd
        add di,4
        add eax,1000h
        loop @B

    ;--- setup ebx/rbx with linear address of _TEXT

        mov bx,_TEXT
        movzx ebx,bx
        shl ebx,4
        add [llg], ebx

    ;--- create IDT

        mov di,5000h
        mov cx,32
        mov edx, offset exception
        add edx, ebx
    make_exc_gates:
        mov eax,edx
        stosw
        mov ax,8
        stosw
        mov ax,8E00h
        stosd
        xor eax, eax
        stosd
        stosd
        add edx,4
        loop make_exc_gates
        mov cx,256-32
    make_int_gates:
        mov eax,offset interrupt
        add eax, ebx
        stosw
        mov ax,8
        stosw
        mov ax,8E00h
        stosd
        xor eax, eax
        stosd
        stosd
        loop make_int_gates

        mov di,5000h
        mov eax, ebx
        add eax, offset clock
        mov es:[di+80h*16+0],ax ; set IRQ 0 handler
        shr eax,16
        mov es:[di+80h*16+6],ax

        mov eax, ebx
        add eax, offset keyboard
        mov es:[di+81h*16+0],ax ; set IRQ 1 handler
        shr eax,16
        mov es:[di+81h*16+6],ax

    ;--- clear NT flag

        pushf
        pop ax
        and ah,0BFh
        push ax
        popf

    ;--- reprogram PIC: change IRQ 0-7 to INT 80h-87h, IRQ 8-15 to INT 88h-8Fh

        cli
        in al,0A1h
        mov ah,al
        in al,21h
        mov [wPICMask],ax
        mov al,10001b       ; begin PIC 1 initialization
        out 20h,al
        mov al,10001b       ; begin PIC 2 initialization
        out 0A0h,al
        mov al,80h          ; IRQ 0-7: interrupts 80h-87h
        out 21h,al
        mov al,88h          ; IRQ 8-15: interrupts 88h-8Fh
        out 0A1h,al
        mov al,100b         ; slave connected to IRQ2
        out 21h,al
        mov al,2
        out 0A1h,al
        mov al,1            ; Intel environment, manual EOI
        out 21h,al
        out 0A1h,al
        in al,21h
        mov al,11111100b    ; enable only clock and keyboard IRQ
        out 21h,al
        in al,0A1h
        mov al,11111111b
        out 0A1h,al

        mov eax,cr4
        or eax,1 shl 5
        mov cr4,eax         ; enable physical-address extensions (PAE)

        mov ecx,0C0000080h  ; EFER MSR
        rdmsr
        or eax,1 shl 8      ; enable long mode
        wrmsr

        lgdt [GDTR]
        lidt [IDTR]

        mov cx,ss
        movzx ecx,cx        ; get base of SS
        shl ecx,4
        movzx esp,sp
        add ecx, esp        ; ECX=linear address of current SS:ESP

        mov eax,cr0
        or eax,80000001h
        mov cr0,eax         ; enable paging + pmode

        db 66h, 0EAh        ; jmp 0008:oooooooo
    llg dd offset long_start
        dw 8

    ;--- switch back to real-mode and exit

    backtoreal:
        cli

        mov eax,cr0
        and eax,7FFFFFFFh   ; disable paging
        mov cr0,eax

        mov ecx,0C0000080h  ; EFER MSR
        rdmsr
        and ah,not 1h       ; disable long mode (EFER.LME=0)
        wrmsr

        mov ax,24           ; set SS,DS and ES to 64k data
        mov ss,ax
        mov ds,ax
        mov es,ax

        mov eax,cr0         ; switch to real mode
        and al,0FEh
        mov cr0, eax

        db 0eah             ; clear instruction cache, CS=real-mode seg
        dw $+4
        dw _TEXT16

        mov ax,STACK        ; SS=real-mode seg
        mov ss, ax
        mov sp,4096

        push cs             ; DS=real-mode _TEXT16 seg
        pop ds

        lidt [nullidt]      ; IDTR=real-mode compatible values

        mov eax,cr4
        and al,not 20h      ; disable physical-address extensions (PAE)
        mov cr4,eax

    ;--- reprogram PIC: change IRQ 0-7 to INT 08h-0Fh, IRQ 8-15 to INT 70h-77h

        mov al,10001b       ; begin PIC 1 initialization
        out 20h,al
        mov al,10001b       ; begin PIC 2 initialization
        out 0A0h,al
        mov al,08h          ; IRQ 0-7: back to ints 8h-Fh
        out 21h,al
        mov al,70h          ; IRQ 8-15: back to ints 70h-77h
        out 0A1h,al
        mov al,100b         ; slave connected to IRQ2
        out 21h,al
        mov al,2
        out 0A1h,al
        mov al,1            ; Intel environment, manual EOI
        out 21h,al
        out 0A1h,al
        in al,21h

        mov ax,[wPICMask]   ; restore PIC masks
        out 21h,al
        mov al,ah
        out 0A1h,al

        sti
        mov ax,4c00h
        int 21h

    _TEXT16 ends

    ;--- here's the 64bit code segment.
    ;--- since 64bit code is always flat but the DOS mz format is segmented,
    ;--- there are restrictions, because the assembler doesn't know the
    ;--- linear address where the 64bit segment will be loaded:
    ;--- + direct addressing with constants isn't possible (mov [0B8000h],rax)
    ;---   since the rip-relative address will be calculated wrong.
    ;--- + 64bit offsets (mov rax, offset <var>) must be adjusted by the linear
    ;---   address where the 64bit segment was loaded (is in rbx).
    ;---
    ;--- rbx must preserve linear address of _TEXT

    _TEXT segment para use64 public 'CODE'

        assume ds:FLAT, es:FLAT

    long_start:

        xor eax,eax
        mov ss,eax
        mov esp,ecx
        sti             ; now interrupts can be used
        call WriteStrX
        db "Hello 64bit",10,0
    nextcmd:
        mov r8b,0       ; r8b will be filled by the keyboard irq routine
    nocmd:
        cmp r8b,0
        jz nocmd
        cmp r8b,1       ; ESC?
        jz esc_pressed
        cmp r8b,13h     ; 'r'?
        jz r_pressed
        call WriteStrX
        db "unknown key ",0
        mov al,r8b
        call WriteB
        call WriteStrX
        db 10,0
        jmp nextcmd

    ;--- 'r' key: display some register contents

    r_pressed:
        call WriteStrX
        db 10,"cr0=",0
        mov rax,cr0
        call WriteQW
        call WriteStrX
        db 10,"cr2=",0
        mov rax,cr2
        call WriteQW
        call WriteStrX
        db 10,"cr3=",0
        mov rax,cr3
        call WriteQW
        call WriteStrX
        db 10,"cr4=",0
        mov rax,cr4
        call WriteQW
        call WriteStrX
        db 10,"cr8=",0
        mov rax,cr8
        call WriteQW
        call WriteStrX
        db 10,0
        jmp nextcmd

    ;--- ESC: back to real-mode

    esc_pressed:
        jmp [bv]
    bv  label fword
        dd offset backtoreal
        dw 16

    ;--- screen output helpers

    ;--- scroll screen up one line
    ;--- rsi = linear address start of last line
    ;--- rbp = linear address of BIOS area (0x400)
    scroll_screen:
        cld
        mov edi,esi
        movzx eax,word ptr [rbp+4Ah]
        push rax
        lea rsi, [rsi+2*rax]
        mov cl, [rbp+84h]
        mul cl
        mov ecx,eax
        rep movsw
        pop rcx
        mov ax,0720h
        rep stosw
        ret

    WriteChr:
        push rbp
        push rdi
        push rsi
        push rbx
        push rcx
        push rdx
        push rax
        mov edi,0B8000h
        mov ebp,400h
        cmp byte ptr [rbp+63h],0B4h
        jnz @F
        xor di,di
    @@:
        movzx ebx, word ptr [rbp+4Eh]
        add edi, ebx
        movzx ebx, byte ptr [rbp+62h]
        mov esi, edi
        movzx ecx, byte ptr [rbx*2+rbp+50h+1] ;ROW
        movzx eax, word ptr [rbp+4Ah]
        mul ecx
        movzx edx, byte ptr [rbx*2+rbp+50h]  ;COL
        add eax, edx
        mov dh,cl
        lea edi, [rdi+rax*2]
        mov al, [rsp]
        cmp al, 10
        jz newline
        mov [rdi], al
        mov byte ptr [rdi+1], 07
        inc dl
        cmp dl, byte ptr [rbp+4Ah]
        jb @F
    newline:
        mov dl, 00
        inc dh
        cmp dh, byte ptr [rbp+84h]
        jbe @F
        dec dh
        call scroll_screen
    @@:
        mov [rbx*2+rbp+50h],dx
        pop rax
        pop rdx
        pop rcx
        pop rbx
        pop rsi
        pop rdi
        pop rbp
        ret

    WriteStr:   ;write string in rdx
        push rsi
        mov rsi, rdx
        cld
    @@:
        lodsb
        and al,al
        jz @F
        call WriteChr
        jmp @B
    @@:
        pop rsi
        ret

    WriteStrX:  ;write string at rip
        push rsi
        mov rsi, [rsp+8]
        cld
    @@:
        lodsb
        and al,al
        jz @F
        call WriteChr
        jmp @B
    @@:
        mov [rsp+8],rsi
        pop rsi
        ret

    WriteQW:        ;write QWord in rax
        push rax
        shr rax,32
        call WriteDW
        pop rax
    WriteDW:
        push rax
        shr rax,16
        call WriteW
        pop rax
    WriteW:
        push rax
        shr rax,8
        call WriteB
        pop rax
    WriteB:     ;write Byte in al
        push rax
        shr rax,4
        call WriteNb
        pop rax
    WriteNb:
        and al,0Fh
        add al,'0'
        cmp al,'9'
        jbe @F
        add al,7
    @@:
        jmp WriteChr

    ;--- exception handler

    exception:
    excno = 0
        repeat 32
        push excno
        jmp @F
        excno = excno+1
        endm
    @@:
        call WriteStrX
        db 10,"Exception ",0
        pop rax
        call WriteB
        call WriteStrX
        db " errcode=",0
        mov rax,[rsp+0]
        call WriteQW
        call WriteStrX
        db " rip=",0
        mov rax,[rsp+8]
        call WriteQW
        call WriteStrX
        db 10,0
    @@:
        jmp $

    ;--- clock and keyboard interrupts

    clock:
        push rbp
        mov ebp,400h
        inc dword ptr [rbp+6Ch]
        pop rbp
    interrupt:              ; handler for all other interrupts
        push rax
        mov al,20h
        out 20h,al
        pop rax
        iretq

    keyboard:
        push rax
        in al,60h
        test al,80h
        jnz @F
        mov r8b, al
    @@:
        in al,61h           ; give finishing information
        out 61h,al          ; to keyboard...
        mov al,20h
        out 20h,al          ; ...and interrupt controller
        pop rax
        iretq

    _TEXT ends

    ;--- 4k stack, used in both modes

    STACK segment use16 para stack 'STACK'
        db 4096 dup (?)
    STACK ends

        end start16

## Win32_5 - Create a Win32 Binary with -bin

    ;--- Win32 "hello world" console application.
    ;--- Uses JWasm's bin output format, so no linker needed.
    ;--- assemble: JWasm -bin -Fo Win32_5.exe Win32_5.ASM

        .386
        option casemap:none

        .nolist
        include winnt.inc   ;include PE image definitions
        .list

    STD_OUTPUT_HANDLE equ -11

    IMAGEBASE equ 400000h

    PEHDR segment dword FLAT

    ;--- define the DOS "MZ" header

        org IMAGEBASE

        IMAGE_DOS_HEADER <"ZM", 80h, 1, 0,4,0,-1,0,200h,0,0,0,0,0,<0>,0,0,<0>,IMAGEREL PEHdr>

        db 0Eh         ;push cs
        db 1Fh         ;pop ds
        db 0BAh,0Eh,0  ;mov dx,text
        db 0B4h,09h    ;mov ah,9
        db 0CDh,21h    ;int 21h
        db 0B8h,01h,4Ch;mov ax,4c01h
        db 0CDh,21h    ;int 21h
        db "This program cannot be run in DOS mode",13,10,'$'

        org IMAGEBASE+80h

    ;--- define the Win32 "PE" header

    PEHdr label byte
        db "PE",0,0
        IMAGE_FILE_HEADER <IMAGE_FILE_MACHINE_I386, num_sections, 0, 0, 0, sizeof IMAGE_OPTIONAL_HEADER32,
            IMAGE_FILE_RELOCS_STRIPPED or IMAGE_FILE_EXECUTABLE_IMAGE or IMAGE_FILE_32BIT_MACHINE or IMAGE_FILE_LOCAL_SYMS_STRIPPED>

        IMAGE_OPTIONAL_HEADER32 { 10Bh, ;magic
            6,0,                        ;linker major, minor
            1000h,1000h,0,              ;sizeof code, initialized data, uninitialized data
            IMAGEREL mainCRTStartup,    ;entry point
            IMAGEREL start_text, IMAGEREL start_rdata,  ;baseof code, data
            IMAGEBASE,    ;imagebase
            1000h,200h,   ;section alignment, file alignment
            4,0,          ;OS major, minor
            0,0,          ;Image major, minor
            4,0,          ;Subsys major, minor
            0,            ;win32 version
            3000h,        ;sizeof image
            1000h,        ;sizeof header
            0,            ;checksum
            IMAGE_SUBSYSTEM_WINDOWS_CUI,
            0,            ;dll characteristics
            100000h,1000h,;stack res,com
            100000h,1000h,;heap res, com
            0,            ;loader flags
            16,           ;number of directories
            <<0,0>,       ;exports
            < IMAGEREL start_idata, SECTIONREL endof_idata >, ;imports
            <0,0>,<0,0>,     ;resource, exception
            <>,<>,<>,<>,     ;security, baserelocs, debug, architecture
            <>,<>,<>,<>,     ;globalptr, tls, load_config, bound_import
            <>,<>,<>,<>>}    ;iat, delay_import, com descriptor, reserved

    ;--- define the section table

    sectiontable label byte
        IMAGE_SECTION_HEADER <".text", <sizeof_text>, IMAGEREL start_text, sizeof_text,
            200h, 0, 0, 0, 0, 060000020h >
        IMAGE_SECTION_HEADER <".rdata", <SECTIONREL endof_idata + sizeof_const>, IMAGEREL start_rdata, SECTIONREL endof_idata + sizeof_const,
            400h, 0, 0, 0, 0, 040000040h >
    num_sections equ ( $ -  sectiontable ) / sizeof IMAGE_SECTION_HEADER

        org IMAGEBASE+200h   ;forces physical size of header to 200h and sets VA to 400200h

    PEHDR ends

    ;--- the ALIGNx segments are needed because
    ;--- section alignment and file alignment are different

    ALIGN1 segment dword public FLAT 'DATA'
        org 0E00h   ; change pc to RVA 1000h
    ALIGN1 ends

    _TEXT segment dword public FLAT 'CODE'
    _TEXT ends

    ALIGN2 segment dword public FLAT 'DATA'
        org 0E00h   ; change pc to RVA 2000h
    ALIGN2 ends

    _IDATA segment dword public FLAT 'DATA'
    start_rdata label byte
    start_idata label byte
    ;--- import descriptors go here
    _IDATA ends
    _IDATA$1 segment dword public FLAT 'DATA'
        IMAGE_IMPORT_DESCRIPTOR <<0>,0,0,0,0>
    ;--- ILT entries go here
    _IDATA$1 ends
    _IDATA$2 segment dword public FLAT 'DATA'
        dd 0    ;--- end of last ILT
    ;--- IAT entries go here
    _IDATA$2 ends
    _IDATA$3 segment dword public FLAT 'DATA'
        dd 0    ;--- end of last IAT
    ;--- import name strings go here
    _IDATA$3 ends
    _IDATA$4 segment dword public FLAT 'DATA'
    endof_idata equ $
    _IDATA$4 ends

    CONST segment dword public FLAT 'DATA'
    start_const label byte
    CONST ends

    DefineImpDll macro name
    _IDATA segment
        IMAGE_IMPORT_DESCRIPTOR <<IMAGEREL name&ILT>,0,0,IMAGEREL name, IMAGEREL name&IAT>
    _IDATA ends
    _IDATA$1 segment
    ifdef ImportDefined
        dd 0  ;terminate previous ILT
    endif
    name&ILT label dword
    _IDATA$1 ends
    _IDATA$2 segment
    ifdef ImportDefined
        dd 0  ;terminate previous IAT
    endif
    name&IAT label dword
    _IDATA$2 ends
    _IDATA$3 segment
    name db @CatStr(!",name, !"),0
        align 4
    _IDATA$3 ends
    ImportDefined equ 1
        endm

    DefineImport macro name
    _IDATA$1 segment
        dd IMAGEREL n&name
    _IDATA$1 ends
    _IDATA$2 segment
    lp&name typedef ptr pr&name
    name    lp&name IMAGEREL n&name
    _IDATA$2 ends
    _IDATA$3 segment
    n&name dw 0
        db @CatStr(!",name, !"),0
        align 4
    _IDATA$3 ends
        endm

    prWriteConsoleA typedef proto stdcall :dword, :dword, :dword, :dword, :dword
    prGetStdHandle  typedef proto stdcall :dword
    prExitProcess   typedef proto stdcall :dword

        DefineImpDll kernel32
        DefineImport ExitProcess
        DefineImport WriteConsoleA
        DefineImport GetStdHandle

    if 0 ;if further dlls are to be imported
    prMessageBoxA   typedef proto stdcall :dword, :dword, :dword, :dword

        DefineImpDll user32
        DefineImport MessageBoxA
    endif

    CONST segment

    string  db 13,10,"hello, world.",13,10

    sizeof_const equ $ - start_const

    CONST ends

    _TEXT segment

        assume ds:FLAT,es:FLAT

    start_text label near

    ;--- start of program

    main proc

    local dwWritten:dword
    local hConsole:dword

        invoke  GetStdHandle, STD_OUTPUT_HANDLE
        mov     hConsole,eax

        invoke  WriteConsoleA, hConsole, addr string, sizeof string, addr dwWritten, 0

        xor     eax,eax
        ret
    main endp

    ;--- entry

    mainCRTStartup proc c

        invoke  main
        invoke  ExitProcess, eax

    mainCRTStartup endp

    sizeof_text equ $ - start_text

        org 200h    ;align size of _TEXT to next 512 byte boundary

    _TEXT ends

        end

## Win32_7 - Usage of OPTION DLLIMPORT and -Fd Switch

    ;--- Win32_7 - Shows how to use OPTION DLLIMPORT and switch -Fd.
    ;---           No import libraries are needed in the link step.
    ;---
    ;--- assemble: JWasm -coff -Fd Win32_7.ASM
    ;--- link:     JWlink format windows pe f Win32_7.OBJ

        .386
        .model FLAT, stdcall
        option casemap:none

    STD_OUTPUT_HANDLE equ -11

       option dllimport:<kernel32>
    WriteConsoleA proto :dword, :dword, :dword, :dword, :dword
    GetStdHandle  proto :dword
    ExitProcess   proto :dword
       option dllimport:<user32>
    MessageBoxA   proto :dword, :dword, :dword, :dword
       option dllimport:<none>

        .const

    msg db 13,10,"hello, world.",13,10
        db 0

        .code

    main proc

    local   written:dword

        invoke  GetStdHandle, STD_OUTPUT_HANDLE
        mov ebx, eax
        invoke  WriteConsoleA, ebx, addr msg, sizeof msg,
                    addr written, 0
        invoke  MessageBoxA, 0, addr msg, 0, 0
        ret

    main endp

    ;--- entry

    start:

        invoke  main
        invoke  ExitProcess, 0

        end start

## Win64_8 - Create a Win64 Binary with -pe

    ;--- create a 64-bit binary with -pe cmdline option
    ;---
    ;---   JWasm -pe Win64_8.asm

        .x64                ; -pe requires to set cpu, model & language
        .model flat, fastcall

        option casemap:none
        option frame:auto   ; generate SEH-compatible prologues and epilogues
        option win64:3      ; init shadow space, reserve stack at PROC level

    ;--- resource IDs
    IDR_MENU1   equ 100
    IDR_BITMAP1 equ 101
    IDM_EXIT    equ 1000

    NULL      equ 0
    LPSTR     typedef ptr
    LPVOID    typedef ptr
    UINT      typedef dword
    BOOL      typedef dword

    ;--- winbase definitions
    HINSTANCE typedef ptr

    ;--- winuser definitions
    HWND      typedef ptr
    HMENU     typedef ptr
    HICON     typedef ptr
    HBRUSH    typedef ptr
    HCURSOR   typedef ptr
    HDC       typedef ptr
    HBITMAP   typedef ptr
    WPARAM    typedef ptr
    LPARAM    typedef qword

    WS_OVERLAPPEDWINDOW equ 0CF0000h
    CW_USEDEFAULT  equ 80000000h
    SW_SHOWDEFAULT equ 10
    SW_SHOWNORMAL  equ 1
    IDC_ARROW      equ 32512
    IDI_APPLICATION equ 32512
    CS_VREDRAW     equ 1
    CS_HREDRAW     equ 2
    COLOR_WINDOW   equ 5

    WM_DESTROY     equ 2
    WM_PAINT       equ 000Fh
    WM_COMMAND     equ 0111h

    proto_WNDPROC typedef proto :HWND,:qword,:WPARAM,:LPARAM
    WNDPROC typedef ptr proto_WNDPROC

    WNDCLASSEXA struct 8
    cbSize          dword   ?
    style           dword   ?
    lpfnWndProc     WNDPROC ?
    cbClsExtra      dword   ?
    cbWndExtra      dword   ?
    hInstance       HINSTANCE ?
    hIcon           HICON   ?
    hCursor         HCURSOR ?
    hbrBackground   HBRUSH  ?
    lpszMenuName    LPSTR   ?
    lpszClassName   LPSTR   ?
    hIconSm         HICON   ?
    WNDCLASSEXA ends

    POINT   struct
    x   sdword  ?
    y   sdword  ?
    POINT   ends

    MSG struct 8
    hwnd    HWND    ?
    message dword   ?
    wParam  WPARAM  ?
    lParam  LPARAM  ?
    time    dword   ?
    pt      POINT   <>
    MSG ends

    RECT struct
    left    sdword  ?
    top     sdword  ?
    right   sdword  ?
    bottom  sdword  ?
    RECT ends

    PAINTSTRUCT struct 8
    hdc         HDC  ?
    fErase      BOOL ?
    rcPaint     RECT <>
    fRestore    BOOL ?
    fIncUpdate  BOOL ?
    rgbReserved byte 32 dup (?)
    PAINTSTRUCT ends

    ;--- wingdi definitions

    DIB_RGB_COLORS  equ 0
    SRCCOPY         equ 00CC0020h

    HGDIOBJ  typedef ptr

    BITMAPINFOHEADER struct
    biSize          dword   ?
    biWidth         sdword  ?
    biHeight        sdword  ?
    biPlanes        word    ?
    biBitCount      word    ?
    biCompression   dword   ?
    biSizeImage     dword   ?
    biXPelsPerMeter sdword  ?
    biYPelsPerMeter sdword  ?
    biClrUsed       dword   ?
    biClrImportant  dword   ?
    BITMAPINFOHEADER ends

        option dllimport:<kernel32>
    GetModuleHandleA proto :LPSTR
    GetCommandLineA  proto
    ExitProcess      proto :UINT

        option dllimport:<user32>
    BeginPaint       proto :HWND, :ptr PAINTSTRUCT
    CreateWindowExA  proto :dword, :LPSTR, :LPSTR, :dword, :sdword, :sdword, :sdword, :sdword, :HWND, :HMENU, :HINSTANCE, :LPVOID
    DefWindowProcA   proto :HWND, :UINT, :WPARAM, :LPARAM
    DestroyWindow    proto :HWND
    DispatchMessageA proto :ptr MSG
    EndPaint         proto :HWND, :ptr PAINTSTRUCT
    GetClientRect    proto :HWND, :ptr RECT
    GetMessageA      proto :ptr MSG, :HWND, :sdword, :sdword
    LoadBitmapA      proto :HINSTANCE, :LPSTR
    LoadCursorA      proto :HINSTANCE, :LPSTR
    LoadIconA        proto :HINSTANCE, :LPSTR
    PostQuitMessage  proto :sdword
    RegisterClassExA proto :ptr WNDCLASSEXA
    ShowWindow       proto :HWND, :sdword
    TranslateMessage proto :ptr MSG
    UpdateWindow     proto :HWND

        option DLLIMPORT:<gdi32>
    BitBlt             proto :HDC, :dword, :dword, :dword, :dword, :HDC, :dword, :dword, :dword
    CreateCompatibleDC proto :HDC
    DeleteDC           proto :HDC
    GetDIBits          proto :HDC, :HBITMAP, :dword, :dword, :ptr, :ptr BITMAPINFO, :dword
    SelectObject       proto :HDC, :HGDIOBJ
        option dllimport:none

    WinMain proto :HINSTANCE, :HINSTANCE, :LPSTR, :UINT

        .data

    ClassName db "SimpleWinClass",0
    AppName  db "Bitmap rendering",0

        .data?

    hInstance HINSTANCE ?
    hBitmap   HBITMAP ?
    CommandLine LPSTR ?

        .code

    WinMainCRTStartup proc FRAME

        invoke GetModuleHandleA, NULL
        mov    hInstance, rax
        invoke GetCommandLineA
        mov    CommandLine, rax
        invoke WinMain, hInstance, NULL, CommandLine, SW_SHOWDEFAULT
        invoke ExitProcess, eax

    WinMainCRTStartup endp

    WinMain proc FRAME hInst:HINSTANCE, hPrevInst:HINSTANCE, CmdLine:LPSTR, CmdShow:UINT

        local wc:WNDCLASSEXA
        local msg:MSG
        local hwnd:HWND

        invoke LoadBitmapA, hInst, IDR_BITMAP1
        mov   hBitmap, rax

        mov   wc.cbSize, sizeof WNDCLASSEXA
        mov   wc.style, CS_HREDRAW or CS_VREDRAW
        lea   rax, [WndProc]
        mov   wc.lpfnWndProc, rax
        mov   wc.cbClsExtra, NULL
        mov   wc.cbWndExtra, NULL
        mov   rcx, hInst
        mov   wc.hInstance, rcx
        mov   wc.hbrBackground, COLOR_WINDOW+1
        mov   wc.lpszMenuName, IDR_MENU1
        lea   rax, [ClassName]
        mov   wc.lpszClassName, rax
        invoke LoadIconA, NULL, IDI_APPLICATION
        mov   wc.hIcon, rax
        mov   wc.hIconSm, rax
        invoke LoadCursorA, NULL, IDC_ARROW
        mov   wc.hCursor,rax
        invoke RegisterClassExA, addr wc
        invoke CreateWindowExA, NULL, ADDR ClassName, ADDR AppName,
               WS_OVERLAPPEDWINDOW, CW_USEDEFAULT,
               CW_USEDEFAULT, CW_USEDEFAULT,CW_USEDEFAULT, NULL, NULL,
               hInst, NULL
        mov   hwnd,rax
        invoke ShowWindow, hwnd, SW_SHOWNORMAL
        invoke UpdateWindow, hwnd
        .while (1)
            invoke GetMessageA, ADDR msg, NULL, 0, 0
            .break .if (!eax)
            invoke TranslateMessage, ADDR msg
            invoke DispatchMessageA, ADDR msg
        .endw
        mov   rax, msg.wParam
        ret
    WinMain endp

    WndProc proc FRAME hWnd:HWND, uMsg:UINT, wParam:WPARAM, lParam:LPARAM

    local hdc2:HDC
    local ps:PAINTSTRUCT
    local rect:RECT
    local bmi:BITMAPINFOHEADER

        .if edx == WM_DESTROY
            invoke PostQuitMessage, NULL
            xor rax,rax
        .elseif edx == WM_COMMAND
            .if wParam == IDM_EXIT
                invoke DestroyWindow, hWnd
            .endif
            xor eax, eax
        .elseif edx == WM_PAINT
            invoke BeginPaint, hWnd, addr ps
            invoke CreateCompatibleDC, ps.hdc
            mov hdc2, rax
            invoke SelectObject, hdc2, hBitmap
            mov bmi.biSize, sizeof BITMAPINFOHEADER
            mov bmi.biBitCount, 0
            invoke GetDIBits, hdc2, hBitmap, 0, 0, 0, addr bmi, DIB_RGB_COLORS
            invoke GetClientRect, hWnd, addr rect
            mov r8d, rect.right
            sub r8d, bmi.biWidth
            jnc @F
            xor r8d, r8d
    @@:
            shr r8d, 1
            mov r9d, rect.bottom
            sub r9d, bmi.biHeight
            jnc @F
            xor r9d, r9d
    @@:
            shr r9d, 1
            invoke BitBlt, ps.hdc, r8d, r9d, bmi.biWidth, bmi.biHeight, hdc2, 0, 0, SRCCOPY
            invoke DeleteDC, hdc2
            invoke EndPaint, hWnd, addr ps

            xor eax,eax
        .else
            invoke DefWindowProcA, rcx, edx, r8, r9
        .endif
        ret
    WndProc endp

    if 1 ;for -pe

    RT_BITMAP equ 2
    RT_MENU   equ 4

    ;--- menu resource flags
    MF_POPUP   equ 10h
    MF_END     equ 80h

    IMAGE_RESOURCE_DIRECTORY struct
    Characteristics      dword ?
    TimeDateStamp        dword ?
    MajorVersion         word  ?
    MinorVersion         word  ?
    NumberOfNamedEntries word  ?
    NumberOfIdEntries    word  ?
    IMAGE_RESOURCE_DIRECTORY ends

    IMAGE_RESOURCE_DIRECTORY_ENTRY struct
    union
    r0      record NameIsString:1, NameOffset:31
    Name_   dword   ?
    Id      word    ?
    ends
    union
    OffsetToData dword   ?
    r1           record	DataIsDirectory:1, OffsetToDirectory:31
    ends
    IMAGE_RESOURCE_DIRECTORY_ENTRY ends

    IMAGE_RESOURCE_DATA_ENTRY struct
    OffsetToData dword ?
    Size_        dword ?
    CodePage     dword ?
    Reserved     dword ?
    IMAGE_RESOURCE_DATA_ENTRY ends

        option dotname

    .rsrc segment dword FLAT public read 'RSRC'

    ;--- define menu IDR_MENU1 and bitmap IDR_BITMAP1

    ;--- root level: enum the resource types
          IMAGE_RESOURCE_DIRECTORY <0,0,0,0,0,2>
          IMAGE_RESOURCE_DIRECTORY_ENTRY < <RT_BITMAP>, <SECTIONREL bms   + 80000000h> >
          IMAGE_RESOURCE_DIRECTORY_ENTRY < <RT_MENU>,   <SECTIONREL menus + 80000000h> >

    ;--- second level: enum the IDs of resource type X
    bms   IMAGE_RESOURCE_DIRECTORY <0,0,0,0,0,1>
          IMAGE_RESOURCE_DIRECTORY_ENTRY < <IDR_BITMAP1>, <SECTIONREL bm1   + 80000000h> >
    menus IMAGE_RESOURCE_DIRECTORY <0,0,0,0,0,1>
          IMAGE_RESOURCE_DIRECTORY_ENTRY < <IDR_MENU1>,   <SECTIONREL menu1 + 80000000h> >

    ;--- third level: enum the languages of ID X
    bm1   IMAGE_RESOURCE_DIRECTORY <0,0,0,0,0,1>
          IMAGE_RESOURCE_DIRECTORY_ENTRY < <409h>, <SECTIONREL bm1_l1> >
    menu1 IMAGE_RESOURCE_DIRECTORY <0,0,0,0,0,1>
          IMAGE_RESOURCE_DIRECTORY_ENTRY < <409h>, <SECTIONREL m1_l1> >

    ;--- last level: define the resource data
    ;--- data for menu IDR_MENU1, language 409h
    m1_l1 IMAGE_RESOURCE_DATA_ENTRY <IMAGEREL m1_l1_data, size_m1_l1, 0, 0>
    m1_l1_data dw 0,0	;menu header
        dw MF_POPUP or MF_END, '&','F','i','l','e',0
        dw MF_END, IDM_EXIT,   'E','&','x','i','t',0
    size_m1_l1 equ $ - m1_l1_data
        align 4

    ;--- data for bitmap IDR_BITMAP1
    bm1_l1 IMAGE_RESOURCE_DATA_ENTRY <IMAGEREL bm1_l1_data, size_bm1_l1, 0, 0>
    bm1_l1_data label word
        incbin <Win32_8.bmp>,14	;skip bitmap file header
    size_bm1_l1 equ $ - ( bm1_l1_data )

    .rsrc ends

    ;--- set /subsystem:windows
    ;--- the PE header is stored in section .hdr$2
        option dotname
    .hdr$2 segment dword FLAT public 'HDR'
        org 5Ch ;position to IMAGE_NT_HEADER64.OptionalHeader.Subsystem
        dw 2    ;2=subsystem windows
    .hdr$2 ends

    endif

    end WinMainCRTStartup

# Appendix C. Errors and Warnings

The warning and error numbers emitted by JWasm differ from Masm's. However, the texts of the messages are pretty much identical.
As in Masm, the first digit shows the severity of the issue: range 1xxx reports a fatal error ( assembly process is stopped ), range 2xxx indicates an error ( assembly process continues, but no object module will be created ) and 4xxx are warnings.

x029 | Multiple base registers not allowed | In 16-bit code, one cannot use both BX and BP in indirect addressing; in 32/64-bit code, ESP/RSP can only appear once in indirect addressing.
x030 | Instruction or register not accepted in current CPU mode |
x031 | Invalid addressing mode with current CPU setting |
x032 | Cannot use TRn-TRn with current CPU setting | The TRx special registers were restricted to 80386 and 80486 cpus.
x033 | Must be index or base register |
x034 | Multiple index registers not allowed |
x035 | Too few bits in RECORD: <symbol> | Size of a Record field must be > 0.
x036 | Scale factor must be 1, 2, 4 or 8 |
x037 | Cannot be used as index register: <register> | Index registers are restricted. In 16-bit mode, only SI and DI can be index registers. In 32-bit mode, all general-purpose registers except ESP can be index registers.
x038 | Base and index register differ in size |
x039 | Expecting comma |
x040 | ORG needs a constant or local offset |
x041 | POP CS is not allowed |
x042 | Only MOV can use special register | The special registers CRx, DRx and TRx can only be moved to/from general purpose registers.
x043 | Cannot use SHORT with CALL | Distance of CALL operands must be NEAR or FAR.
x044 | Only SHORT jump distance is allowed | Some jump instructions accept short distances only (JCXZ, JECXZ, LOOPx).
x045 | Syntax error |
x046 | Prefix must be followed by an instruction |
x047 | Syntax error: Unexpected colon |
x048 | Operands must be the same size: <size op1> - <size op2> |
x049 | Invalid instruction operands |
x050 | Jump distance not possible in current CPU mode | Jcc instructions won't accept type coercions that increase the jump distance (i.e. "jz NEAR PTR label") if current cpu is < 80386.
x051 | Immediate data out of range |
x052 | Can not use short or near modifiers with this instruction |
x053 | Jump out of range by <num> byte(s) | A short distance must be in the range -128 to +127.
x054 | currently not used. |
x055 | Initializer value too large |
x056 | Symbol already defined: <symbol> |
x057 | Offset magnitude too large for specified size |
x058 | Magnitude of offset exceeds 16 bit | This is a warning (level 3). Occurs, for example, if an instruction like "mov ax, ds:[1000000h]" is found in a 16-bit segment. Masm accepts without complaints, but truncates the offset to 16-bit ( JWasm does NOT truncate ).
x059 | Operand 2 too big |
x060 | Operand 1 too small |
x061 | Line too long | Size of a line ( after concatenation) is restricted to 600. Note that Masm's line limit is 512; however, that limit is for 'original' lines only - due to macro expansion, the 'expanded' line size may exceed the limit.
x062 | Too many tokens in a line | The number of tokens in a line is restricted to 150. Note that the corresponding Masm error message is 'statement too complex'.
x063 | Symbol not defined: <struct/union>.<member> |
x064 | Expression expected: <token> |
x065 | Constant expected | A constant (numeric) value is expected in the current context. Note that a label - more exactly: the offset part of a label's address - is not a constant value, since the final value is calculated by the linker ( or the OS loader ) only.
x066 | Constant operand is expected | The expression evaluator accepts a constant only in the current context.
x067 | .ELSE clause already occured in this .IF block | An .IF block may contain 0 or 1 .ELSE clauses and it must be the last clause before .ENDIF.
x068 | Multiple overrides |
x069 | Segment, group or segment register expected | The operand before the colon operator (:) must be a segment, group or segment register.
x070 | Identifier too long | Length of identifers is restricted to 247. This is a hard limit for OMF output format, and it's also Masm's limit. For other formats, the limit may be extended by adjusting and recompiling the source code.
x071 | Invalid operand size for instruction |
x072 | Not supported: <directive> | Message is displayed if one of the follwing options is specified: OPTION READONLY, OPTION EXPR16, OPTION OLDMACROS. Those are currently not supported.
x073 | Size not specified, assuming: <type> | this is a warning. <type> may be BYTE, WORD or DWORD. The message may occur if an immediate value is written to an untyped memory reference, for example:
    mov [ebx], 1
JWasm makes a guess and displays this warning, while Masm will display an error in such cases.
x074 | Floating-point initializer ignored |
x075 | Only SHORT and NEAR jump distance is allowed | Conditional jump (Jcc) instruction destination cannot be far.
x076 | Initializer magnitude too large for specified size |
x077 | Segment attribute is defined already: <attribute> |
x078 | Segment definition changed: %s, %s |
x079 | Class name too long | Segment class names are restricted to 255 in size.
x080 | Block nesting error: %s |
x081 | Segment attribute is unknown: %s |
x082 | Must be in segment block | Instructions and directives that generate code or data must be inside a segment block.
x083 | Segment not defined: <segment> |
x084 | Colon is expected |
x085 | Invalid qualified type: %s |
x086 | Qualified type is expected |
x087 |  |
x088 | Library name is missing |
x089 | Cannot access label through segment registers: <label> |
x090 | Line too long after expansion: <line> |
x091 | Language type must be specified |
x092 | PROC, MACRO or macro loop directive must precede LOCAL |
x093 | Cannot nest procedures |
x094 | VARARG requires C calling convention |
x095 | Multiple .MODEL directives, .MODEL ignored |
x096 | Model is not declared | Without a model, simplified segment directives ( .CODE, .DATA, .CONST, .DATA?, .STACK, .FARDATA and .FARDATA? ) and directives .STARTUP, .EXIT cannot be used.
x097 | Backquote missing: `<identifier> |
x098 | COMMENT delimiter expected |
x099 | END directive required at end of file |
x100 | Nesting level too deep |
x101 | Macro nesting level too deep |
x102 | Symbol not defined : <symbol> |
x103 |  |
x104 | No filename specified. |
x105 | Out of Memory | This is a fatal error. With the 8086-version of jwasm, JWASMR, you'll see this error if you try to assemble something that contains a few thousand symbols. The 32- or 64-bit versions of jwasm should always have enough memory on modern machines.
x106 | Cannot open file: "<file>" [<error code>] | Error code ENOENT means "file not found". Other error codes are displayed as numbers
x107 | Cannot close file: <file> [<error code>] |
x108 | File write error: <file> [<error code>] | Usually happens if output media is read-only or full.
x109 | Invalid command-line option: <option> |
x110 | Internal error in <source file>(<line>) | This error shouldn't be seen in the release version. It's displayed if the internal assert() function is called, which usually is done when a "virtually impossible" error condition has occurred.
x111 | Expecting closing square bracket |
x112 | Expecting file name |
x113 | Too many errors | Use commandline option -e to set the max. number of errors that are displayed
x114 | forced error <message> | Generic "forced error" message
x115 | forced error: Value not equal to 0: <value> <text> | Error emitted by the .ERRNZ directive.
x116 | forced error: Value equal to 0: <value> <text> | Error emitted by the .ERRE directive.
x117 | forced error: symbol defined: <symbol> | Error emitted by the .ERRDEF directive.
x118 | forced error: symbol not defined: <symbol> | Error emitted by the .ERRNDEF directive.
x119 | forced error: string blank : <string> | Error emitted by the .ERRB directive.
x120 | forced error: string not blank : <string> | Error emitted by the .ERRNB directive.
x121 | forced error: strings not equal : <string> : <string> | Error emitted by the .ERRDIF and .ERRDIFI directives.
x122 | forced error: strings equal : <string> : <string> | Error emitted by the .ERRIDN and .ERRIDNI directives.
x123 | <file>(<line>): Included by | Additional error information if error occured in an include file.
x124 | <file>(<line>)[<macro>]: Macro called from | Additional error information if error occured inside a macro.
x125 | <file>(<line>): iteration <iteration>: Macro called from | Additional error information if error occured inside a loop macro (FOR, FORC, REPEAT, ...).
x126 | <file>(<line>): Main line code | Additional error information if error occured inside an include file or a macro.
x127 | Extending jump |
x128 | Directive ignored: %s |
x129 | number must be a power of 2 |
x130 | Incompatible with segment alignment: %s |
x131 | Segment expected: %s |
x132 | Incompatible CPU mode for 32-bit segment |
x133 | Far call is converted to near call. |
x134 | CPU option %s is not valid for selected CPU. |
x135 | Segment '%s' is in another group already |
x136 | Symbol type conflict: %s |
x137 | Conflicting parameter definition: %s |
x138 | PROC and PROTO calling convention conflict |
x139 | Non-benign %s redefinition: %s |
x140 | Too many bits in RECORD: %s | Size of a RECORD is limited to 32 bits for 16-/32-bit code and 64 bits for 64-bit code.
x141 | Statement not allowed inside structure definition |
x142 | Unmatched block nesting: %s |
x143 | Symbol redefinition: %s |
x144 | Text item required |
x145 | INVOKE argument type mismatch: argument %u |
x146 | Too few arguments to INVOKE: %s |
x147 | VARARG parameter must be last | The macro parameter qualifier VARARG can only be added to the last parameter.
x148 | LABEL parameter must be first | The macro parameter qualifier LABEL ( JWasm extension ) can only be added to the first parameter.
x149 | Too many arguments in macro call: %s | This is a warning. Macro is invoked with more arguments than expected.
x150 | Missing operator in expression |
x151 | Unexpected literal found in expression: %s | Literals enclosed in <> or {} are items processed by the preprocessor or to initialize "structured" data items. If they're used otherwise, this error will occur.
x152 | Initializer must be a string or single item: %s |
x153 | Too many initial values for structure: %s |
x154 | Too many initial values for array: %s |
x155 | String or text literal too long | Length of text literals is limited to 568. Note that this differs from Masm's limit of 255.
x156 | PROLOGUE must be macro function | The user-defined prologue macro must be a macro function, that is, there must be an EXITM somewhere inside that returns a literal.
x157 | EPILOGUE must be macro procedure: %s | The user-defined epilogue macro must be a macro procedure, that is, there must NOT be an EXITM somewhere inside that returns a literal.
x158 | Reserved word expected | OPTION NOKEYWORD and OPTION RENAMEKEYWORD both expect a reserved word as argument.
x159 | INVOKE requires prototype for procedure |
x160 | Invalid type for data declaration: %s |
x161 | Operand must be RECORD type or field |
x162 | Unmatched macro nesting |
x163 | Empty (null) string |
x164 | No segment information to create fixup: %s |
x165 | Register value overwritten by INVOKE |
x166 | Missing quotation mark in string |
x167 | Divide by zero in expression |
x168 | General Failure |
x169 | Cannot have implicit far jump or call to near label |
x170 | Invalid use of register |
x171 | Distance invalid for current segment |
x172 | Initializer magnitude too large: %s |
x173 | Cannot add two relocatable labels |
x174 | Cannot define as public or external: <symbol_name> | Text macros, macros, stack variables, structure fields or segment/groups cannot be public or external.
x175 | Positive value expected |
x176 | FAR not allowed in FLAT model COMM variables |
x177 | Too many arguments to INVOKE |
x178 | Directive must appear inside a macro |
x179 | Invalid type expression |
x180 | Cannot declare scoped code label as PUBLIC: <label> |
x181 | Invalid radix tag |
x182 | Instruction operand must have size | The instruction allows operands with more than just one size, and the wanted size cannot be guessed from the current operands.
x183 | Use of register assumed to ERROR |
x184 | Instructions and initialized data not supported in <seg_type> segments | <seg_type> may be BSS or AT. Such segments don't have data.
x185 | Literal expected after '=' |
x186 | No 4k Page-aligned segments in MS386 OMF | A 4K page-aligned segment isn't compatible with MS OMF format, it's a Phar Lab extension. This warning won't appear in the standard version.
x187 |  |
x188 | Operand must be relocatable |
x189 | Constant or relocatable label expected |
x190 | [ELSE]IF2/.ERR2 not allowed, single-pass assembler |
x191 | Expression too complex for UNTILCXZ |
x192 | Operands must be in same segment |
x193 | Invalid use of external symbol: <symbol_name> |
x194 | For -coff leading underscore required for start label: <start_label> |
x195 | Invalid command-line value, default is used: %s |
x196 | Unknown fixup type: %u at <segment>.<offset> |
x197 | Unsupported fixup type for <format>: <type> |
x198 | Invalid fixup type for <format> <type> at location <segment>.<offset> |
x199 | Syntax error in control-flow directive |
x200 | Invalid .model parameter for flat model |
x201 | Output format doesn't support externals: <symbol> | In formats BIN and MZ all references must be local to the module.
x202 | Invalid start label for -bin |
x203 | No start label defined | Warning, format MZ only: MZ-binaries usually have a start label. In some cases (i.e. overlays) a missing start label may be ok.
x204 | No stack defined | Warning, format MZ only: MZ-binaries usually have a stack. In some cases (i.e. overlays) a missing stack may be ok.
x205 | Invalid alignment - value must be 2^n (n=4..15) |
x206 | Index value past end of string: <value> | The index argument of SUBSTR or INSTR is beyond the string argument length
x207 | Count value too large |
x208 | Count must be positive or zero |
x209 | Syntax error: <item> | The parser found an item that has no meaning in the current context
x210 |  |
x211 | Model must be FLAT | In 64-bit mode, or if output format is -pe, there's no segmented model available.
x212 | Must use floating-point initializer |
x213 | ORG directive not allowed in unions |
x214 | Struct alignment must be 1, 2, 4, 8, 16 or 32 |
x215 | Structure cannot be instanced | A structure that has size 0 or that contains an ORG directive cannot be instanced.
x216 | Missing angle bracket or brace in literal |
x217 | Nondigit in number: <number> |
x218 | 16bit fixup for 32bit label: <symbol> | A warning that the generated code might not do what is expected.
x219 | Too many macro placeholders | The number of parameters and locals for a macro must not exceed 256
x220 | Missing macro argument: %s, parameter %u |
x221 | Doesn't work with 32-bit segments: <directive> | Directives .STARTUP and .EXIT work for 16-bit only.
x222 | Segment exceeds 64k limit: %s | In MZ format, 16-bit segments are restricted to 64k. |
x223 | Not supported with OMF format: %s |
x224 | Not supported with current output format: %s | The directive or feature isn't supported by all formats. For example, segment-related directives or attributes won't make much sense for flat formats like COFF or ELF.
x225 | Unknown default prologue argument: %s |
x226 | LOADDS ignored in flat model |
x227 | Missing right parenthesis in expression |
x228 | Invalid operand for <operator>: <operand> |
x229 | Structure improperly initialized: %s |
x230 | Expected: %s |
x231 | Invalid data initializer |
x232 | Expected data label | Some operators ( LENGTH, SIZE ) work with data labels only.
x233 | Expression must be a code address |
x234 | -n Option needs a valid name parameter |
x235 | Constant value too large: <value> | the value of the constant doesn't fit in 64 or - if it is a number to be assigned to a symbolic constant - 32 bits.
x236 | Text macro was used before definition | this is a warning only. However, using text macros before they have been defined will force JWasm to do a full second pass, which increases assembly time.
x237 | Offset size incompatible with current segment |
x238 | Instruction form requires 80386 |
x239 | Group/Segment offset size conflict: <group offset> - <segment offset> | Segments within a group must all have the same offset size.
x240 | Assembly passes reached: <passes> | Although this is a warning only it usually indicates a severe problem. The assembler is very probably unable to calculate "final" values of all labels and has to be terminated by pressing Ctrl-C.
x241 | Filename parameter must be enclosed in <> or quotes | The INCBIN directive requires delimiters for its filename.
x242 | Start address on END directive ignored with .STARTUP |
x243 | Invalid symbol type in expression: <symbol> | The expression evaluator has encountered a symbol that is meaningless in expressions, for example a (text) macro.
x244 | Missing right parenthesis |
x245 | Directive must be in control block | .ELSE, .ELSEIF and .ENDIF are valid inside .IF-blocks, .BREAK, .CONTINUE may occur inside .WHILE- or .REPEAT-blocks, .ENDW needs a preceding .WHILE and .UNTIL needs a preceding .REPEAT.
x246 | Expected: memory model | the .MODEL directive needs at least one parameter, the memory model.
x247 | Type is wrong size for register |
x248 | IF[n]DEF expects a plain symbol as argument | this is a warning. Masm accepts any expression as argument for directives [ELSE]IF[N]DEF, but the result probably isn't always what has been expected.
x249 | Jump destination must specify a label |
x250 | Ignored: <attribute> | An attribute or parameter of a directive was found, but not handled. See Known Bugs and missing Features for details about what features aren't implemented yet.
x251 | Missing argument for cmdline option |
x252 | Invalid coprocessor register |
x253 | Registers AH-DH may not be used with SPL-DIL or R8-R15 | 64-bit only.
x254 | .ENDPROLOG found before EH directives | 64-bit only.
x255 | Missing FRAME in PROC, no unwind code will be generated | 64-bit only.
x256 | Bad alignment for offset in unwind code | 64-bit only.
x257 | Nonzero value expected |
x258 | Size of prolog too big, must be < 256 bytes | 64-bit only.
x259 | Missing .ENDPROLOG: %s | 64-bit only.
x260 | .SAFESEH argument must be a PROC |
x261 | Directive ignored without -%s switch |
x262 | ELF GNU extensions (8/16-bit relocations) used | This is a warning only. The extensions are not "official", but the GNU linker LD will understand them.
x263 | Syntax error in expression |
x264 | Macro label not defined: %s | The target of a GOTO must be within the very same macro.
x265 | Procedure argument or local not referenced: %s | This warning is displayed only if at least -W3 is specified.
x266 | Group definition too large, truncated: <group_name> | The size of the OMF record that is to define a group would exceed 4 kB. However, to see this error you'll have to define a group that is to comprise more than 1000 segments,
x267 | COMM variable exceeds 64K: <variable> | in 16-bit, the size of a COMM variable is restricted to 64 kB.
x268 | Must be public or external: %s | Names that are to be known by the linker must be public or external.
x269 | parameter/local name is reserved word: %s | This is a warning. The names of macro parameters or locals have highest priority and hence the reserved word will become inaccessible within the macro.
x270 | real or BCD number not allowed |
x271 | structure field expected |
x272 | Constant value too large: <value> | the value of the constant doesn't fit in 64 or - if it is a number to be assigned to a symbolic constant - 32 bits.
x273 | ELSE clause already occured in this IF block | An IF block may contain 0 or 1 ELSE clauses and it must be the last clause before ENDIF.
x274 | Illegal use of segment register |
x275 | Group exceeds 64K: <group> | MZ format only: a group that contains 16-bit segments cannot be larger than 64 kB, because the group must fit into a physical segment. Also, due to how a group is located in the binary, the max. size may be even up to 15 bytes smaller than 64 kB!
x276 | EXPORT must be FAR: <symbol> | A 16-bit procedure that is to be exported must be declared with the FAR distance attribute.
x277 | Start label not in a 16-bit segment | MZ format only: the start label is in a 32- or 64-bit segment. The resulting MZ binary won't run without further modification, i.e. adding a DOS-extender stub.
x278 | ADDR32 fixup to '<symbol>' at location <segment>.<offset> | 64-bit PE format only: a 32-bit fixup was detected, but base address is above or equal 0x80000000.
x279 | 64-bit label referenced with 32-bit fixup |
x280 | Too many segments/sections defined for output format | For OMF, max. number of segments is 32767. For COFF, max. number of sections is 65535.
x281 | Object format doesn't support anonymous fixups, location: <offset> | Anonymous fixups are possible for the OMF object format only.
x282 | Segment/Section ignored in binary formats | This is a warning. Informational sections for the linker are ignored for binary formats.
x283 | Opcode size suffix ignored for segment registers | This is a warning if opcodes PUSHW/PUSHD are used to push segment registers. The expectation might be that an appropriate size suffix (0x66) is generated by the assembler, but this assumption is incorrect.
x284 | Prologue not at PROC start | This is a warning, caused for example by data definition directives at the procedure's start. This is unusual, but accepted ( by JWasm and Masm ). It might cause unexpected results, though.

# Appendix D. Differences between Masm 6 and Masm 8

This is not strictly JWasm-related, but since a lot of documentation that can be found about Masm still refers to Masm v6 or Masm v6.1 only, it's useful to list the differences.

- default output format has been changed from OMF to COFF in Masm 8.
- expression evaluator calculations are done in 64-bit instead of 32-bit. This is not always reflected in the listing file, where the values may be truncated to 32-bit.
- some segment attributes have been added in Masm 8 to cover the COFF section attribute bits. These are:
  - INFO
  - DISCARD
  - NOCACHE
  - NOPAGE
  - SHARED
  - EXECUTE
  - READ
  - WRITE
  - ALIAS
  - ALIGN
- the -safeseh commandline option and the .SAFESEH directive have been added in Masm 8.
- Masm 8 understands a few new data types:
  - OWORD - 128-bit integer
  - MMWORD - 64-bit data type for MMX
  - XMMWORD - 128-bit data type for SSE
- several unary operators are new for Masm 8:
  - LOW32 - returns the lower 32-bit of an expression
  - HIGH32 - returns the upper 32-bit of an expression
  - IMAGEREL - returns the image relative offset of an expression (aka RVA). COFF format only.
  - SECTIONREL - returns the section relative offset of an expression. COFF format only.
  Please note: LOW32 and HIGH32 operators won't accept plain numbers with values that exceed 32-bits.
- Masm 8 understands instruction sets up to SSE3. The last version of Masm 6, version 6.15, supports SSE2 only. Masm 8 also understands Intel's VMX and AMD's SVM extensions ( x86 virtualization ).
- Masm 8 needs at least Windows 2000, it won't run on Windows 9x (without hacks).
- Masm 8 needs a MS VC runtime dll - MSVCR80.DLL - to run, while Masm 6 was a stand-alone binary.
- Finally, Masm 8 fixes some bugs and introduces a few new ones. One of the new bugs is that Masm 8 has problems with wildcards in filenames; entering

      ml.exe -c *.asm

  to assemble all assembly files in a directory won't work as expected.

# Appendix E. Restrictions of precompiled 16-bit Binary JWASMR.EXE

JWASMR lacks some features of the other precompiled binaries:

- no support for long filenames.
- no support for Open Watcom's fastcall register convention.
- supports OMF, BIN and MZ output formats only.
- no support for 64-bit, SSSE3, SSE4 and AVX.
- no support for OPTION variants that are specific for COFF, ELF or 64-bit.
- no support for OPTION CODEVIEW directive.
- no support for directive LABEL's array size syntax extension.

Since the JWasm source is available, one may enable this or that feature if really needed, though.

# Appendix F. Additional Features of JWasm's Debug Version

Note: there are no precompiled debug versions of JWasm available. Such versions have to be created from the source code. See the comments in the makefiles how to do that.

The debug version offers the following additional commandline options:

-af | Display all files used in assembly process
-ce | Cause an exception
-dm | Display all messages
-dr | Display reserved words
-drh | Display reserved words hash table
-ds | Display global symbols
-dsh | Display global symbols hash table
-dt | Display debug trace
-ls | Display preprocessed line storage
-nbp | Disable back-patching
-nfp | Do full subsequent passes ( disables "fastpass" )
-pm=<n> | Stop assembly after n passes
-sp | Skip preprocessor step