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| -rw-r--r-- | Documentation/contributing/coding_style.md | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/Documentation/contributing/coding_style.md b/Documentation/contributing/coding_style.md index 656454545d..3314030df0 100644 --- a/Documentation/contributing/coding_style.md +++ b/Documentation/contributing/coding_style.md @@ -960,6 +960,41 @@ asm ("magic %reg1, #42nt" : /* outputs */ : /* inputs */ : /* clobbers */); ``` +GCC extensions +-------------- + +GCC is the only officially-supported compiler for coreboot, and a +variety of its C language extensions are heavily used throughout the +code base. There have been occasional attempts to add clang as a second +compiler option, which is generally compatible to the same language +extensions that have been long-established by GCC. + +Some GCC extensions (e.g. inline assembly) are basically required for +proper firmware development. Others enable more safe or flexible +coding patterns than can be expressed with standard C (e.g. statement +expressions and `typeof()` to avoid double evaluation in macros like +`MAX()`). Yet others just add some simple convenience and reduce +boilerplate (e.g. `void *` arithmetic). + +Since some GCC extensions are necessary either way, there is no gain +from avoiding other GCC extensions elsewhere. The use of all official +GCC extensions is expressly allowed within coreboot. In cases where an +extension can be replaced by a 100% equivalent C standard feature with +no extra boilerplate or loss of readability, the C standard feature +should be preferred (this usually only happens when GCC retains an +older pre-standardization extension for backwards compatibility, e.g. +the old pre-C99 syntax for designated initializers). But if there is +any advantage offered by the GCC extension (e.g. using GCC zero-length +arrays instead of C99 variable-length arrays because they don't inhibit +`sizeof()`), there is no reason to deprive ourselves of that, and "this +is not C standard compliant" should not be a reason to argue against +its use in reviews. + +This rule only applies to explicit GCC extensions listed in the +"Extensions to the C Language Family" section of the GCC manual. Code +should never rely on incidental GCC translation behavior that is not +explicitly documented as a feature and could change at any moment. + References ---------- |