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diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle index 2b90d328b3b..c58b236bbe0 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 |