Gnu arm assembler manual

This text follows that approach, presenting a number of techniques for writing time-efficient code in assembly. The accompanying programming labs provide experience applying these techniques to the implementation of entertaining and informative applications, with many that measure and report the number of processor clock cycles required to execute the assembly language functions or that demonstrate specific optimization techniques.

Chapters Address alignment, execution time, and the. REPT and. 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.

There are cases where it may make sense to use this in objects to be bound into an application itself so as to override a versioned symbol from a shared library. The name2 part of the name is the actual name of the symbol by which it will be externally referenced. The name name itself is merely a name of convenience that is used so that it is possible to have definitions for multiple versions of a function within a single source file, and so that the compiler can unambiguously know which version of a function is being mentioned.

The nodename portion of the alias should be the name of a node specified in the version script supplied to the linker when building a shared library. If you are attempting to override a versioned symbol from a shared library, then nodename should correspond to the nodename of the symbol you are trying to override.

Tags are used to link structure definitions in the symbol table with instances of those structures. Tells as to assemble the following statements onto the end of the text subsection numbered subsection , which is an absolute expression.

If subsection is omitted, subsection number zero is used. Use heading as the title second line, immediately after the source file name and pagenumber when generating assembly listings.

While most of the available assembler directives are valid regardless of the target architecture, some directives are machine dependent. 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.