System V ABI: Difference between revisions

The '''System V Application Binary Interface''' is a set of specifications that detail [[Calling Conventions|calling conventions]], [[Object Files|object file formats]], [[Executable Formats|executable file formats]], dynamic linking semantics, and much more for systems that complies with the ''X/Open Common Application Environment Specification'' and the ''System V Interface Definition''. It is today the standard ABI used by the major Unix operating systems such as Linux, the BSD systems, and many others. The [[Executable and Linkable Format]] ((ELF) is part of the System V ABI.

Many of the advanced feature such as dynamic linking are optional and loading a simple statically linked [[ELF]] program is straightforward. Earlier versions of the standard were more ambitious and attempted to standardize software package installation formats and X11 details, while these obsolete details are disregarded today. The ABI is well-understood by common operating system's development tools like [[binutilsBinutils]] and [[GCC]]. Toolchains such as <tt>i686-elf-gcc</tt> generate code and executable files according to this ABI.

This is a 32-bit platform. The stack grows downwards. Parameters to functions are passed on the stack in reverse order such that the first parameter is the last value pushed to the stack, which will then be the lowest value on the stack. Parameters passed on the stack may be modified by the called function. Functions are called using the <tt>call</tt> instruction that pushes the address of the next instruction to the stack and jumps to the operand. Functions return to the caller using the <tt>ret</tt> instruction that pops a value from the stack and jump to it. The stack is 4-byte aligned all the time, on older systems and those honouring the SYSV psABI. On some newer systems, the stack is additionally 16-byte aligned just before the call instruction is called (usually those that want to support SSE instructions); consult your manual (GNU/Linux on i386 has recently become such a system, but code mixing with 4-byte stack alignment-assuming code is possible).

Additionally, if you compile with [[GCC]], it assumes the stack is 16-byte aligned (not just 4-byte aligned) when the <tt>call</tt> instruction in the caller was executed. This is required to properly store SSE values on the stack, as they require 16-byte alignment, or other values (such as 64-bit values) with higher-than-4-byte alignment. As a special exception, GCC assumes the stack is not properly aligned and realigns it when entering <tt>main</tt> or if the <tt>attribute ((force_align_arg_pointer))</tt> is set on the function.

'''TODO:''' ''Ensure whether these are the latest official links. These documents are simply what I foundcould find through a quick online search.''

** [http://www.sco.com/developers/devspecsgabi/gabi41latest/contents.pdfhtml System V ABI - OlderLatest Base Document]

** [http://www.sco.com/developers/devspecs/abi386-4gabi41.pdf System V ABI - Intel386 ArchitectureOlder ProcessorBase SupplementDocument]

** [http://www.x86-64akkadia.org/documentationdrepper/abitls.pdf SystemELF VHandling ABIFor Thread-Local AMD64 Architecture Processor SupplementStorage]

** [httphttps://math-atlas.sourceforgegitlab.netcom/develx86-psABIs/assembly/mipsabi64.pdfx86-64-ABI System V ABI - MIPSpro™AMD64 64-BitArchitecture Processor Supplement]

** [http://math-atlaswww.sourceforgesco.netcom/develdevelopers/assemblydevspecs/007abi386-2816-0054.pdf System V ABI - MIPSpro™Intel386 N32Architecture ABIProcessor HandbookSupplement]

** [http://math-atlassoftware.sourceforgeintel.netcom/develsites/assemblydefault/elfspec_ppcfiles/forum/278102/k1om-psabi-1.0.pdf System V ABI - PowerPCK1OM Architecture Processor Supplement]

** [http://math-atlas.sourceforge.net/devel/assembly/abi_sysV_sparcmipsabi32.pdf System V ABI - SPARC®MIPS RISC Processor Supplement]

** [http://math-atlas.sourceforge.net/devel/assembly/64.psabi.1.33.psmipsabi64.Zpdf System V ABI - SPARC®MIPSpro™ Version 9 Processor Supplement64-Bit]

** [http://softwaremath-atlas.intelsourceforge.comnet/sitesdevel/defaultassembly/files/forum/278102/k1om007-psabi2816-1.0005.pdf System V ABI - K1OMMIPSpro™ ArchitectureN32 ProcessorABI SupplementHandbook]