Gnu assembly manual

Both spelling variants are equivalent. The code from file is assembled as if it followed the point of the. Quotation marks are required around file. Expect zero or more expressions , of any section, separated by commas.

For each expression, emit a number that, at run time, is the value of that expression. The byte order and bit size of the number depends on what kind of target the assembly is for.

Evaluate a sequence of statements assigning different values to symbol. The sequence of statements starts at the. For each value , symbol is set to value , and the sequence of statements is assembled. If no value is listed, the sequence of statements is assembled once, with symbol set to the null string. For each character in value , symbol is set to the character, and the sequence of statements is assembled.

Reserve length an absolute expression bytes for a local common denoted by symbol. The section and value of symbol are those of the new local common. The addresses are allocated in the bss section, so that at run-time the bytes start off zeroed. Symbol is not declared global see section. Some targets permit a third argument to be used with.

This argument specifies the desired alignment of the symbol in the bss section. Change the logical line number. The next line has that logical line number. Therefore any other statements on the current line after a statement separator character are reported as on logical line number line-number - 1. One day as will no longer support this directive: it is recognized only for compatibility with existing assembler programs.

Even though this is a directive associated with the a. Inside a. Mark the current section so that the linker only includes a single copy of it. This may be used to include the same section in several different object files, but ensure that the linker will only include it once in the final output file. Duplicate sections are detected based on the section name, so it should be unique.

This directive is only supported by a few object file formats; as of this writing, the only object file format which supports it is the Portable Executable format used on Windows NT. The type argument is optional. If specified, it must be one of the following strings. For example:. If val is non-zero, this tells as to enter MRI mode. If val is zero, this tells as to exit MRI mode. This change affects code assembled until the next.

Control in conjunction with the. These two directives maintain an internal counter which is zero initially. Assembly listings are generated whenever the counter is greater than zero. By default, listings are disabled. The commands.

For example, this definition specifies a macro sum that puts a sequence of numbers into memory:. This directive expects zero or more bignums, separated by commas.

For each bignum, it emits a byte integer. The term "octa" comes from contexts in which a "word" is two bytes; hence octa -word for 16 bytes. Advance the location counter of the current section to new-lc. That is, you can't use. To be compatible with former assemblers, if the section of new-lc is absolute, as issues a warning, then pretends the section of new-lc is the same as the current subsection.

Because as tries to assemble programs in one pass, new-lc may not be undefined. If you really detest this restriction we eagerly await a chance to share your improved assembler. Beware that the origin is relative to the start of the section, not to the start of the subsection. This is compatible with other people's assemblers. When the location counter of the current subsection is advanced, the intervening bytes are filled with fill which should be an absolute expression.

If the comma and fill are omitted, fill defaults to zero. The first expression which must be absolute is the number of low-order zero bits the location counter must have after advancement. Use this directive to declare the number of lines--and, optionally, the number of columns--to use for each page, when generating listings. If you do not use.

You may omit the comma and columns specification; the default width is columns. If you specify lines as 0 , no formfeeds are generated save those explicitly specified with.

For each bignum, it emits an 8-byte integer. If the bignum won't fit in 8 bytes, it prints a warning message; and just takes the lowest order 8 bytes of the bignum. The term "quad" comes from contexts in which a "word" is two bytes; hence quad -word for 8 bytes. Repeat the sequence of lines between the. Use subheading as the title third line, immediately after the title line when generating assembly listings. This directive affects subsequent pages, as well as the current page if it appears within ten lines of the top of a page.

Set the storage-class value for a symbol. This directive may only be used inside a. Storage class may flag whether a symbol is static or external, or it may record further symbolic debugging information. Use the. This directive is only supported for targets that actually support arbitrarily named sections; on a. For COFF targets, the. Each flag is a single character.

The following flags are recognized: b bss section uninitialized data n section is not loaded w writable section d data section r read-only section x executable section If no flags are specified, the default flags depend upon the section name. If the section name is not recognized, the default will be for the section to be loaded and writable. If the optional argument to the. For ELF targets, the. If the section name is not recognized, the default will be for the section to have none of the above flags: it will not be allocated in memory, nor writable, nor executable.

The section will contain data. For ELF targets, the assembler supports another type of. There may be a sequence of comma separated flags: alloc section is allocatable write section is writable execinstr section is executable.

This changes symbol 's value and type to conform to expression. If symbol was flagged as external, it remains flagged see section Symbol Attributes. If you. In some configurations, however,. This directive emits size bytes, each of value fill.

Both size and fill are absolute expressions. If the comma and fill are omitted, fill is assumed to be zero. Warning: In most versions of the GNU assembler, the directive. All emit symbols see section Symbols , for use by symbolic debuggers.

The symbols are not entered in the as hash table: they cannot be referenced elsewhere in the source file. Up to five fields are required:. If a warning is detected while reading a. This is compatible with earlier assemblers! Copy the characters in str to the object file. You may specify more than one string to copy, separated by commas. Unless otherwise specified for a particular machine, the assembler marks the end of each string with a 0 byte.

You can use any of the escape sequences described in section Strings. This is only supported on ELF platforms, and is typically used when assembling files to be linked into a shared library. GAS supports two comment styles: [3]. Single line comments have a few different formats varying on which architecture is being assembled for. Being the back-end for a popular compiler suite, namely GCC, the GNU Assembler is very widely used in compiling modern open source software.

Since version 2. History The first version of GAS was released in General syntax GAS supports a general syntax that works for all of the supported architectures. Directives GAS uses assembler directives also known as pseudo ops , which are keywords beginning with a period that behave similarly to preprocessor directives in the C programming language.

Intel syntax Since version 2. See also Free and open-source software portal. Retrieved Jan 10, Retrieved 28 July