1@c Copyright (C) 1988-2020 Free Software Foundation, Inc. 2@c This is part of the GCC manual. 3@c For copying conditions, see the file gcc.texi. 4 5@node Portability 6@chapter GCC and Portability 7@cindex portability 8@cindex GCC and portability 9 10GCC itself aims to be portable to any machine where @code{int} is at least 11a 32-bit type. It aims to target machines with a flat (non-segmented) byte 12addressed data address space (the code address space can be separate). 13Target ABIs may have 8, 16, 32 or 64-bit @code{int} type. @code{char} 14can be wider than 8 bits. 15 16GCC gets most of the information about the target machine from a machine 17description which gives an algebraic formula for each of the machine's 18instructions. This is a very clean way to describe the target. But when 19the compiler needs information that is difficult to express in this 20fashion, ad-hoc parameters have been defined for machine descriptions. 21The purpose of portability is to reduce the total work needed on the 22compiler; it was not of interest for its own sake. 23 24@cindex endianness 25@cindex autoincrement addressing, availability 26@findex abort 27GCC does not contain machine dependent code, but it does contain code 28that depends on machine parameters such as endianness (whether the most 29significant byte has the highest or lowest address of the bytes in a word) 30and the availability of autoincrement addressing. In the RTL-generation 31pass, it is often necessary to have multiple strategies for generating code 32for a particular kind of syntax tree, strategies that are usable for different 33combinations of parameters. Often, not all possible cases have been 34addressed, but only the common ones or only the ones that have been 35encountered. As a result, a new target may require additional 36strategies. You will know 37if this happens because the compiler will call @code{abort}. Fortunately, 38the new strategies can be added in a machine-independent fashion, and will 39affect only the target machines that need them. 40