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author | Josh Triplett <josh@joshtriplett.org> | 2012-03-30 13:37:10 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-03-30 16:03:15 -0700 |
commit | 9a7c48b7c3d58835b3a91d86c55e0ae77d15ddd5 (patch) | |
tree | 9a7728d24c9721d7e9e5458b7f76d565265fa9ae | |
parent | 21106b0114f75cff199d6834f676877c3edae928 (diff) | |
download | linux-stable-9a7c48b7c3d58835b3a91d86c55e0ae77d15ddd5.tar.gz linux-stable-9a7c48b7c3d58835b3a91d86c55e0ae77d15ddd5.tar.bz2 linux-stable-9a7c48b7c3d58835b3a91d86c55e0ae77d15ddd5.zip |
Documentation: CodingStyle: add inline assembly guidelines
Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | Documentation/CodingStyle | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle index 2b90d328b3ba..c58b236bbe04 100644 --- a/Documentation/CodingStyle +++ b/Documentation/CodingStyle @@ -793,6 +793,35 @@ own custom mode, or may have some other magic method for making indentation work correctly. + Chapter 19: Inline assembly + +In architecture-specific code, you may need to use inline assembly to interface +with CPU or platform functionality. Don't hesitate to do so when necessary. +However, don't use inline assembly gratuitously when C can do the job. You can +and should poke hardware from C when possible. + +Consider writing simple helper functions that wrap common bits of inline +assembly, rather than repeatedly writing them with slight variations. Remember +that inline assembly can use C parameters. + +Large, non-trivial assembly functions should go in .S files, with corresponding +C prototypes defined in C header files. The C prototypes for assembly +functions should use "asmlinkage". + +You may need to mark your asm statement as volatile, to prevent GCC from +removing it if GCC doesn't notice any side effects. You don't always need to +do so, though, and doing so unnecessarily can limit optimization. + +When writing a single inline assembly statement containing multiple +instructions, put each instruction on a separate line in a separate quoted +string, and end each string except the last with \n\t to properly indent the +next instruction in the assembly output: + + asm ("magic %reg1, #42\n\t" + "more_magic %reg2, %reg3" + : /* outputs */ : /* inputs */ : /* clobbers */); + + Appendix I: References |