NASM(1) 						      General Commands Manual							   NASM(1)

NAME

       nasm - the Netwide Assembler, a portable 80x86 assembler

SYNOPSIS

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

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 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 left.

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

       -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 processed.

       -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 stderr.

       -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.

       -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).

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

   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 assem-
       blers.

       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-defin-
       able.)

       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  direc-
       tive 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  UPPER-
       CASE,  which directs that all segment, group and symbol names output to the object file should be in uppercase. Note that the actual assem-
       bly 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  min-
       param.  %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  defini-
       tions) using %repl.  Labels and %define macros specific to the top context may be defined by prefixing their names with %$, and things spe-
       cific 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.sourceforge.org.

SEE ALSO

       as(1), ld(1).

							   The Netwide Assembler Project						   NASM(1)