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NASM(1) 										  NASM(1)

       nasm - the Netwide Assembler, a portable 80x86 assembler

       nasm  [	-@  response  file ] [ -f format ] [ -o outfile ] [ -l listfile ] [ options...	]
       nasm -h
       nasm -v

       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 exten-
       sions for a raw binary file. Failing that, the output file name will be `nasm.out'.

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

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

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

       -d macro[=value]
	      Same as the -D option.

       -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.

       -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 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.

       -i directory
	      Same as the -I option.

       -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

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

       -O number
	      optimize branch offsets (-O0 disables, default).

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

       -P file
	      Specifies a file to be pre-included, before the main source file starts to be  pro-

       -p file
	      Same as the -P option.

       -r     Causes nasm to exit immediately, after displaying its version number.  (obsolete)

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

       -t     Causes nasm to assemble in SciTech TASM compatible mode

       -U macro
	      Undefines a single-line macro.

       -u macro
	      Same as the -U option.

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

	      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).

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

       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'.

       SECTION	name  or  SEGMENT name causes nasm to direct all following code to the named sec-
       tion. 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-

       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 generat-
       ing 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  struc-
       ture  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.

       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.

       Single-line macros are defined using the %define or %idefine commands, in a similar  fash-
       ion  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>

       Again,  these  macros may be overloaded. The trailing plus sign indicates that any parame-
       ters after the last one get subsumed, with their separating commas, into the last  parame-
       ter.  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 informa-
       tion 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  con-
       text may be defined by prefixing their names with %$, and things specific to the next con-
       text 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  condi-
       tion  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.

       Please report bugs through the bug tracker function at http://nasm.sourceforge.org.

       as(1), ld(1).

				  The Netwide Assembler Project 			  NASM(1)
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