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NASM(1)			 The Netwide Assembler Project		       NASM(1)

NAME
       nasm - the Netwide Assembler, a portable	80x86 assembler

SYNOPSIS
       nasm [-@	response file] [-f format] [-o outfile]	[-l listfile]
       [options...] filename

DESCRIPTION
       The nasm	command	assembles the file filename and	directs	output to the
       file outfile if specified. If outfile is	not specified, nasm 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
       `nasm.out'.

OPTIONS
       -@ filename
	   Causes nasm to process options from filename	as if they were
	   included on the command line.

       -a
	   Causes nasm to assemble the given input file	without	first applying
	   the macro preprocessor.

       -D|-d macro[=value]
	   Pre-defines a single-line macro.

       -E|-e
	   Causes nasm to preprocess the given input file, and write the
	   output to stdout (or	the specified output file name), and not
	   actually assemble anything.

       -f format
	   Specifies the output	file format. To	see a list of valid output
	   formats, use	the -hf	option.

       -F format
	   Specifies the debug information format. To see a list of valid
	   output formats, use the -y option (for example -felf	-y).

       -g
	   Causes nasm to generate debug information in	selected format.

       -h
	   Causes nasm to exit immediately, after giving a summary of its
	   invocation options.

       -hf
	   Same	as -h ,	but also lists all valid output	formats.

       -I|-i directory
	   Adds	a directory to the search path for include files. The
	   directory specification must	include	the trailing slash, as it will
	   be directly prepended to the	name of	the include file.

       -l listfile
	   Causes an assembly listing to be directed to	the given file,	in
	   which the original source is	displayed on the right hand side (plus
	   the source for included files and the expansions of multi-line
	   macros) and the generated code is shown in hex on the left.

       -M
	   Causes nasm to output Makefile-style	dependencies to	stdout;	normal
	   output is suppressed.

       -MG file
	   Same	as -M but assumes that missing Makefile	dependecies are
	   generated and added to dependency list without a prefix.

       -MF file
	   Output Makefile-style dependencies to the specified file.

       -MD file
	   Same	as a combination of -M and -MF options.

       -MT file
	   Override the	default	name of	the dependency target dependency
	   target name.	This is	normally the same as the output	filename,
	   specified by	the -o option.

       -MQ file
	   The same as -MT except it tries to quote characters that have
	   special meaning in Makefile syntax. This is not foolproof, as not
	   all characters with special meaning are quotable in Make.

       -MP
	   Emit	phony target.

       -O number
	   Optimize branch offsets.

	   o   -O0: No optimization

	   o   -O1: Minimal optimization

	   o   -Ox: Multipass optimization (default)

       -o outfile
	   Specifies a precise name for	the output file, overriding nasm's
	   default means of determining	it.

       -P|-p file
	   Specifies a file to be pre-included,	before the main	source file
	   starts to be	processed.

       -s
	   Causes nasm to send its error messages and/or help text to stdout
	   instead of stderr.

       -t
	   Causes nasm to assemble in SciTech TASM compatible mode.

       -U|-u macro
	   Undefines a single-line macro.

       -v
	   Causes nasm to exit immediately, after displaying its version
	   number.

       *-W[no-]foo'
	   Causes nasm to enable or disable certain classes of warning
	   messages, in	gcc-like style,	for example -Worphan-labels or
	   -Wno-orphan-labels.

       -w[+-]foo
	   Causes nasm to enable or disable certain classes of warning
	   messages, for example -w+orphan-labels or -w-macro-params.

       -X format
	   Specifies error reporting format (gnu or vc).

       -y
	   Causes nasm to list supported debug formats.

       -Z filename
	   Causes nasm to redirect error messages to filename. This option
	   exists to support operating systems on which	stderr is not easily
	   redirected.

       --prefix, --postfix
	   Prepend or append (respectively) the	given argument to all global
	   or extern variables.

SYNTAX
       This man	page does not fully describe the syntax	of nasm's assembly
       language, but does give a summary of the	differences from other
       assemblers.

       Registers have no leading `%' sign, unlike gas, and floating-point
       stack registers are referred to as st0, st1, and	so on.

       Floating-point instructions may use either the single-operand form or
       the double. A TO	keyword	is provided; thus, one could either write

	   fadd	st0,st1
	   fadd	st1,st0

       or one could use	the alternative	single-operand forms

	   fadd	st1
	   fadd	to st1

       Uninitialised storage is	reserved using the RESB, RESW, RESD, RESQ,
       REST and	RESO pseudo-opcodes, each taking one parameter which gives the
       number of bytes,	words, doublewords, quadwords or ten-byte words	to
       reserve.

       Repetition of data items	is not done by the DUP keyword as seen in DOS
       assemblers, but by the use of the TIMES prefix, like this:

	   message: times 3 db 'abc'
		    times 64-$+message db 0

       which defines the string	abcabcabc, followed by the right number	of
       zero bytes to make the total length up to 64 bytes.

       Symbol references are always understood to be immediate (i.e. the
       address of the symbol), unless square brackets are used,	in which case
       the contents of the memory location are used. Thus:

	   mov ax,wordvar

       loads AX	with the address of the	variable wordvar, whereas

	   mov ax,[wordvar]
	   mov ax,[wordvar+1]
	   mov ax,[es:wordvar+bx]

       all refer to the	contents of memory locations. The syntaxes

	   mov ax,es:wordvar[bx]
	   es mov ax,wordvar[1]

       are not legal at	all, although the use of a segment register name as an
       instruction prefix is valid, and	can be used with instructions such as
       LODSB which can't be overridden any other way.

       Constants may be	expressed numerically in most formats: a trailing H, Q
       or B denotes hex, octal or binary respectively, and a leading `0x' or
       `$' denotes hex as well.	Leading	zeros are not treated specially	at
       all. Character constants	may be enclosed	in single or double quotes;
       there is	no escape character. The ordering is little-endian (reversed),
       so that the character constant 'abcd' denotes 0x64636261	and not
       0x61626364.

       Local labels begin with a period, and their `locality' is granted by
       the assembler prepending	the name of the	previous non-local symbol.
       Thus declaring a	label `.loop' after a label `label' has	actually
       defined a symbol	called `label.loop'.

DIRECTIVES
       SECTION name or SEGMENT name causes nasm	to direct all following	code
       to the named section. Section names vary	with output file format,
       although	most formats support the names .text, .data and	.bss. (The
       exception is the	obj format, in which all segments are user-definable.)

       ABSOLUTE	address	causes nasm to position	its notional assembly point at
       an absolute address: so no code or data may be generated, but you can
       use RESB, RESW and RESD to move the assembly point further on, and you
       can define labels. So this directive may	be used	to define data
       structures. When	you have finished doing	absolute assembly, you must
       issue another SECTION directive to return to normal assembly.

       BITS 16,	BITS 32	or BITS	64 switches the	default	processor mode for
       which nasm is generating	code: it is equivalent to USE16	or USE32 in
       DOS assemblers.

       EXTERN symbol and GLOBAL	symbol import and export symbol	definitions,
       respectively, from and to other modules.	Note that the GLOBAL directive
       must appear before the definition of the	symbol it refers to.

       STRUC strucname and ENDSTRUC, when used to bracket a number of RESB,
       RESW or similar instructions, define a data structure. In addition to
       defining	the offsets of the structure members, the construct also
       defines a symbol	for the	size of	the structure, which is	simply the
       structure name with size	tacked on to the end.

FORMAT-SPECIFIC	DIRECTIVES
       ORG address is used by the bin flat-form	binary output format, and
       specifies the address at	which the output code will eventually be
       loaded.

       GROUP grpname seg1 seg2... is used by the obj (Microsoft	16-bit)	output
       format, and defines segment groups. This	format also uses UPPERCASE,
       which directs that all segment, group and symbol	names output to	the
       object file should be in	uppercase. Note	that the actual	assembly is
       still case sensitive.

       LIBRARY libname is used by the rdf output format, and causes a
       dependency record to be written to the output file which	indicates that
       the program requires a certain library in order to run.

MACRO PREPROCESSOR
       Single-line macros are defined using the	%define	or %idefine commands,
       in a similar fashion to the C preprocessor. They	can be overloaded with
       respect to number of parameters,	although defining a macro with no
       parameters prevents the definition of any macro with the	same name
       taking parameters, and vice versa. %define defines macros whose names
       match case-sensitively, whereas %idefine	defines	case-insensitive
       macros.

       Multi-line macros are defined using %macro and %imacro (the distinction
       is the same as that between %define and %idefine), whose	syntax is as
       follows

	   %macro name minprm[-maxprm][+][.nolist] [defaults]
		   <some lines of macro	expansion text>
	   %endmacro

       Again, these macros may be overloaded. The trailing plus	sign indicates
       that any	parameters after the last one get subsumed, with their
       separating commas, into the last	parameter. The defaults	part can be
       used to specify defaults	for unspecified	macro parameters after
       minparam. %endm is a valid synonym for %endmacro.

       To refer	to the macro parameters	within a macro expansion, you use %1,
       %2 and so on. You can also enforce that a macro parameter should
       contain a condition code	by using %+1, and you can invert the condition
       code by using %-1. You can also define a	label specific to a macro
       invocation by prefixing it with a double	`%' sign.

       Files can be included using the %include	directive, which works like C.

       The preprocessor	has a `context stack', which may be used by one	macro
       to store	information that a later one will retrieve. You	can push a
       context on the stack using %push, remove	one using %pop,	and change the
       name of the top context (without	disturbing any associated definitions)
       using %repl. Labels and %define macros specific to the top context may
       be defined by prefixing their names with	%$, and	things specific	to the
       next context down with %$$, and so on.

       Conditional assembly is done by means of	%ifdef,	%ifndef, %else and
       %endif as in C. (Except that %ifdef can accept several putative macro
       names, and will evaluate	TRUE if	any of them is defined.) In addition,
       the directives %ifctx and %ifnctx can be	used to	condition on the name
       of the top context on the context stack.	The obvious set	of `else-if'
       directives, %elifdef, %elifndef,	%elifctx and %elifnctx are also
       supported.

BUGS
       Please report bugs through the bug tracker function at http://nasm.us.

SEE ALSO
       as(1), ld(1).

NASM				  02/21/2015			       NASM(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | SYNTAX | DIRECTIVES | FORMAT-SPECIFIC DIRECTIVES | MACRO PREPROCESSOR | BUGS | SEE ALSO

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