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diff --git a/contrib/gcc/doc/compat.texi b/contrib/gcc/doc/compat.texi new file mode 100644 index 0000000..3e4ef89 --- /dev/null +++ b/contrib/gcc/doc/compat.texi @@ -0,0 +1,115 @@ +@c Copyright (C) 2002 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Compatibility +@chapter Binary Compatibility +@cindex binary compatibility +@cindex ABI +@cindex application binary interface + +Binary compatibility encompasses several related concepts: + +@table @dfn +@item application binary interface (ABI) +The set of runtime conventions followed by all of the tools that deal +with binary representations of a program, including compilers, assemblers, +linkers, and language runtime support. +Some ABIs are formal with a written specification, possibly designed +by multiple interested parties. Others are simply the way things are +actually done by a particular set of tools. + +@item ABI conformance +A compiler conforms to an ABI if it generates code that follows all of +the specifications enumerated by that ABI@. +A library conforms to an ABI if it is implemented according to that ABI@. +An application conforms to an ABI if it is built using tools that conform +to that ABI and does not contain source code that specifically changes +behavior specified by the ABI@. + +@item calling conventions +Calling conventions are a subset of an ABI that specify of how arguments +are passed and function results are returned. + +@item interoperability +Different sets of tools are interoperable if they generate files that +can be used in the same program. The set of tools includes compilers, +assemblers, linkers, libraries, header files, startup files, and debuggers. +Binaries produced by different sets of tools are not interoperable unless +they implement the same ABI@. This applies to different versions of the +same tools as well as tools from different vendors. + +@item intercallability +Whether a function in a binary built by one set of tools can call a +function in a binary built by a different set of tools is a subset +of interoperability. + +@item implementation-defined features +Language standards include lists of implementation-defined features whose +behavior can vary from one implementation to another. Some of these +features are normally covered by a platform's ABI and others are not. +The features that are not covered by an ABI generally affect how a +program behaves, but not intercallability. + +@item compatibility +Conformance to the same ABI and the same behavior of implementation-defined +features are both relevant for compatibility. +@end table + +The application binary interface implemented by a C or C++ compiler +affects code generation and runtime support for: + +@itemize @bullet +@item +size and alignment of data types +@item +layout of structured types +@item +calling conventions +@item +register usage conventions +@item +interfaces for runtime arithmetic support +@item +object file formats +@end itemize + +In addition, the application binary interface implemented by a C++ compiler +affects code generation and runtime support for: +@itemize @bullet +@item +name mangling +@item +exception handling +@item +invoking constructors and destructors +@item +layout, alignment, and padding of classes +@item +layout and alignment of virtual tables +@end itemize + +Some GCC compilation options cause the compiler to generate code that +does not conform to the platform's default ABI@. Other options cause +different program behavior for implementation-defined features that are +not covered by an ABI@. These options are provided for consistency with +other compilers that do not follow the platform's default ABI or the +usual behavior of implementation-defined features for the platform. +Be very careful about using such options. + +Most platforms have a well-defined ABI that covers C code, but ABIs +that cover C++ functionality are not yet common. + +Starting with GCC 3.2, GCC binary conventions for C++ are based on a +written, vendor-neutral C++ ABI that was designed to be specific to +64-bit Itanium but also includes generic specifications that apply to +any platform. +This C++ ABI is also implemented by other compiler vendors on some +platforms, notably GNU/Linux and BSD systems. +We have tried hard to provide a stable ABI that will be compatible with +future GCC releases, but it is possible that we will encounter problems +that make this difficult. Such problems could include different +interpretations of the C++ ABI by different vendors, bugs in the ABI, or +bugs in the implementation of the ABI in different compilers. +GCC's @code{-Wabi} switch warns when G++ generates code that is +probably not compatible with the C++ ABI@. |