Tribblix: manual page: yasm.1

YASM(1) The Yasm Modular Assembler YASM(1)

NAME

yasm - The Yasm Modular Assembler

SYNOPSIS

yasm [-f format] [-o outfile] [other options...] {infile}

yasm -h

DESCRIPTION

The Yasm Modular Assembler is a portable, retargetable assembler
written under the "new" (2 or 3 clause) BSD license. Yasm currently
supports the x86 and AMD64 instruction sets, accepts NASM and GAS
assembler syntaxes, outputs binary, ELF32, ELF64, COFF, Win32, and
Win64 object formats, and generates source debugging information in
STABS, DWARF 2, and CodeView 8 formats.

YASM consists of the yasm command, libyasm, the core backend library,
and a large number of modules. Currently, libyasm and the loadable
modules are statically built into the yasm executable.

The yasm command assembles the file infile and directs output to the
file outfile if specified. If outfile is not specified, yasm will
derive a default output file name from the name of its input file,
usually by appending .o or .obj, or by removing all extensions for a
raw binary file. Failing that, the output file name will be yasm.out.

If called with an infile of "-", yasm assembles the standard input
and directs output to the file outfile, or yasm.out if no outfile is
specified.

OPTIONS

Many options may be given in one of two forms: either a dash followed
by a single letter, or two dashes followed by a long option name.
Options are listed in alphabetical order.

General Options

-a arch or --arch=arch: Select target architecture
Selects the target architecture. The default architecture is
"x86", which supports both the IA-32 and derivatives and AMD64
instruction sets. To print a list of available architectures to
standard output, use "help" as arch. See yasm_arch(7) for a list
of supported architectures.

-f format or --oformat=format: Select object format
Selects the output object format. The default object format is
"bin", which is a flat format binary with no relocation. To print
a list of available object formats to standard output, use "help"
as format. See yasm_objfmts(7) for a list of supported object
formats.

-g debug or --dformat=debug: Select debugging format
Selects the debugging format for debug information. Debugging
information can be used by a debugger to associate executable
code back to the source file or get data structure and type
information. Available debug formats vary between different
object formats; yasm will error when an invalid combination is
selected. The default object format is selected by the object
format. To print a list of available debugging formats to
standard output, use "help" as debug. See yasm_dbgfmts(7) for a
list of supported debugging formats.

-L list or --lformat=list: Select list file format
Selects the format/style of the output list file. List files
typically intermix the original source with the machine code
generated by the assembler. The default list format is "nasm",
which mimics the NASM list file format. To print a list of
available list file formats to standard output, use "help" as
list.

-l listfile or --list=listfile: Specify list filename
Specifies the name of the output list file. If this option is not
used, no list file is generated.

-m machine or --machine=machine: Select target machine architecture
Selects the target machine architecture. Essentially a subtype of
the selected architecture, the machine type selects between major
subsets of an architecture. For example, for the "x86"
architecture, the two available machines are "x86", which is used
for the IA-32 and derivative 32-bit instruction set, and "amd64",
which is used for the 64-bit instruction set. This
differentiation is required to generate the proper object file
for relocatable object formats such as COFF and ELF. To print a
list of available machines for a given architecture to standard
output, use "help" as machine and the given architecture using -a
arch. See yasm_arch(7) for more details.

-o filename or --objfile=filename: Specify object filename
Specifies the name of the output file, overriding any default
name generated by Yasm.

-p parser or --parser=parser: Select parser
Selects the parser (the assembler syntax). The default parser is
"nasm", which emulates the syntax of NASM, the Netwide Assembler.
Another available parser is "gas", which emulates the syntax of
GNU AS. To print a list of available parsers to standard output,
use "help" as parser. See yasm_parsers(7) for a list of supported
parsers.

-r preproc or --preproc=preproc: Select preprocessor
Selects the preprocessor to use on the input file before passing
it to the parser. Preprocessors often provide macro functionality
that is not included in the main parser. The default preprocessor
is "nasm", which is an imported version of the actual NASM
preprocessor. A "raw" preprocessor is also available, which
simply skips the preprocessing step, passing the input file
directly to the parser. To print a list of available
preprocessors to standard output, use "help" as preproc.

-h or --help: Print a summary of options
Prints a summary of invocation options. All other options are
ignored, and no output file is generated.

--version: Get the Yasm version
This option causes Yasm to prints the version number of Yasm as
well as a license summary to standard output. All other options
are ignored, and no output file is generated.

Warning Options

-W options have two contrary forms: -Wname and -Wno-name. Only the
non-default forms are shown here.

The warning options are handled in the order given on the command
line, so if -w is followed by -Worphan-labels, all warnings are
turned off except for orphan-labels.

-w: Inhibit all warning messages
This option causes Yasm to inhibit all warning messages. As
discussed above, this option may be followed by other options to
re-enable specified warnings.

-Werror: Treat warnings as errors
This option causes Yasm to treat all warnings as errors. Normally
warnings do not prevent an object file from being generated and
do not result in a failure exit status from yasm, whereas errors
do. This option makes warnings equivalent to errors in terms of
this behavior.

-Wno-unrecognized-char: Do not warn on unrecognized input characters
Causes Yasm to not warn on unrecognized characters found in the
input. Normally Yasm will generate a warning for any non-ASCII
character found in the input file.

-Worphan-labels: Warn on labels lacking a trailing option
When using the NASM-compatible parser, causes Yasm to warn about
labels found alone on a line without a trailing colon. While
these are legal labels in NASM syntax, they may be unintentional,
due to typos or macro definition ordering.

-X style: Change error/warning reporting style
Selects a specific output style for error and warning messages.
The default is "gnu" style, which mimics the output of gcc. The
"vc" style is also available, which mimics the output of
Microsoft's Visual C++ compiler.

This option is available so that Yasm integrates more naturally
into IDE environments such as Visual Studio or Emacs, allowing
the IDE to correctly recognize the error/warning message as such
and link back to the offending line of source code.

Preprocessor Options

While these preprocessor options theoretically will affect any
preprocessor, the only preprocessor currently in Yasm is the "nasm"
preprocessor.

-D macro[=value]: Pre-define a macro
Pre-defines a single-line macro. The value is optional (if no
value is given, the macro is still defined, but to an empty
value).

-e or --preproc-only: Only preprocess
Stops assembly after the preprocessing stage; preprocessed output
is sent to the specified output name or, if no output name is
specified, the standard output. No object file is produced.

-I path: Add include file path
Adds directory path to the search path for include files. The
search path defaults to only including the directory in which the
source file resides.

-P filename: Pre-include a file
Pre-includes file filename, making it look as though filename was
prepended to the input. Can be useful for prepending multi-line
macros that the -D can't support.

-U macro: Undefine a macro
Undefines a single-line macro (may be either a built-in macro or
one defined earlier in the command line with -D.

EXAMPLES

To assemble NASM syntax, 32-bit x86 source source.asm into ELF file
source.o, warning on orphan labels:

yasm -f elf32 -Worphan-labels source.asm

To assemble NASM syntax AMD64 source x.asm into Win64 file
object.obj:

yasm -f win64 -o object.obj x.asm

To assemble already preprocessed NASM syntax x86 source y.asm into
flat binary file y.com:

yasm -f bin -r raw -o y.com y.asm

DIAGNOSTICS

The yasm command exits 0 on success, and nonzero if an error occurs.

COMPATIBILITY

Yasm's NASM parser and preprocessor, while they strive to be as
compatible as possible with NASM, have a few incompatibilities due to
YASM's different internal structure.

Yasm's GAS parser and preprocessor are missing a number of features
present in GNU AS.

RESTRICTIONS

As object files are often architecture and machine dependent, not all
combinations of object formats, architectures, and machines are
legal; trying to use an invalid combination will result in an error.

There is no support for symbol maps.

BUGS

When using the "x86" architecture, it is overly easy to generate
AMD64 code (using the BITS 64 directive) and generate a 32-bit object
file (by failing to specify -m amd64 or selecting a 64-bit object
format such as ELF64 on the command line).

AUTHOR

Peter Johnson <peter@tortall.net>
Author.