1*ec02198aSmrg@c Copyright (C) 1988-2020 Free Software Foundation, Inc. 210d565efSmrg@c This is part of the GCC manual. 310d565efSmrg@c For copying conditions, see the file gcc.texi. 410d565efSmrg 510d565efSmrg@node Portability 610d565efSmrg@chapter GCC and Portability 710d565efSmrg@cindex portability 810d565efSmrg@cindex GCC and portability 910d565efSmrg 1010d565efSmrgGCC itself aims to be portable to any machine where @code{int} is at least 1110d565efSmrga 32-bit type. It aims to target machines with a flat (non-segmented) byte 1210d565efSmrgaddressed data address space (the code address space can be separate). 1310d565efSmrgTarget ABIs may have 8, 16, 32 or 64-bit @code{int} type. @code{char} 1410d565efSmrgcan be wider than 8 bits. 1510d565efSmrg 1610d565efSmrgGCC gets most of the information about the target machine from a machine 1710d565efSmrgdescription which gives an algebraic formula for each of the machine's 1810d565efSmrginstructions. This is a very clean way to describe the target. But when 1910d565efSmrgthe compiler needs information that is difficult to express in this 2010d565efSmrgfashion, ad-hoc parameters have been defined for machine descriptions. 2110d565efSmrgThe purpose of portability is to reduce the total work needed on the 2210d565efSmrgcompiler; it was not of interest for its own sake. 2310d565efSmrg 2410d565efSmrg@cindex endianness 2510d565efSmrg@cindex autoincrement addressing, availability 2610d565efSmrg@findex abort 2710d565efSmrgGCC does not contain machine dependent code, but it does contain code 2810d565efSmrgthat depends on machine parameters such as endianness (whether the most 2910d565efSmrgsignificant byte has the highest or lowest address of the bytes in a word) 3010d565efSmrgand the availability of autoincrement addressing. In the RTL-generation 3110d565efSmrgpass, it is often necessary to have multiple strategies for generating code 3210d565efSmrgfor a particular kind of syntax tree, strategies that are usable for different 3310d565efSmrgcombinations of parameters. Often, not all possible cases have been 3410d565efSmrgaddressed, but only the common ones or only the ones that have been 3510d565efSmrgencountered. As a result, a new target may require additional 3610d565efSmrgstrategies. You will know 3710d565efSmrgif this happens because the compiler will call @code{abort}. Fortunately, 3810d565efSmrgthe new strategies can be added in a machine-independent fashion, and will 3910d565efSmrgaffect only the target machines that need them. 40