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RedHat 9 (Linux i386) - man page for nasm (redhat section 1)

NASM(1) 										  NASM(1)

NAME
       nasm - the Netwide Assembler - portable 80x86 assembler

SYNOPSIS
       nasm [ -f format ] [ -o outfile ] [ options...  ] infile
       nasm -h
       nasm -r

DESCRIPTION
       The nasm command assembles the file infile and directs output to the file outfile if spec-
       ified. 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
       -h     Causes nasm to exit immediately, after giving a summary of its invocation  options,
	      and listing all its supported output file formats.

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

       -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.

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

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

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

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

       -f format
	      Specifies  the output file format. Formats include bin, to produce flat-form binary
	      files, and aout and elf to produce Linux a.out and ELF object files, respectively.

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

       -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.

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

       -w[+-]foo
	      Causes  nasm  to enable or disable certain classes of warning messages, for example
	      -w+orphan-labels or -w-macro-params to, respectively, enable warnings about  labels
	      alone  on  lines or disable warnings about incorrect numbers of parameters in macro
	      calls.

       -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.

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

       -p file
	      Same as the -P option.

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

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

       -U macro
	      Undefines a single-line macro.

       -u macro
	      Same as the -U option.

   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  and  REST  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  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-
       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 or BITS 32 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 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.

   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 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>
	     %endmacro

       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.

BUGS
       There  is  a reported seg-fault on some (Linux) systems with some large source files. This
       appears to be very hard to reproduce. All other known bugs have been fixed...

RESTRICTIONS
       There is no support for listing files, symbol maps, or debugging object-file records.  The
       advanced features of the ELF and Win32 object file formats are not supported, and there is
       no means for warning the programmer against using an instruction beyond the capability  of
       the target processor.

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

				  The Netwide Assembler Project 			  NASM(1)


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