NASM(1)                                                                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.

       -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.
              -O0 :No optimization (default)
              -O1 :Minimal optimization
              -Ox :Multipass optimization (recommended)

       -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.

       --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.sourceforge.org.

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



                         The Netwide Assembler Project                 NASM(1)
