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
-O1 :Minimal optimization -Ox :Multipass optimization
(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.
- --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.
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).