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authorDmitry Torokhov <dmitry.torokhov@gmail.com>2012-04-22 10:28:35 +0400
committerDmitry Torokhov <dmitry.torokhov@gmail.com>2012-04-22 10:28:35 +0400
commit57b8628bb0ac4e47c806e45c5bbd89282e93869b (patch)
treeee9289f0898054474b7e5054abdb3ffb78666436 /Documentation/CodingStyle
parent486c8aba39e5f194519cd5c0e85e5d1de8b74b03 (diff)
parent66f75a5d028beaf67c931435fdc3e7823125730c (diff)
downloadlinux-57b8628bb0ac4e47c806e45c5bbd89282e93869b.tar.xz
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@@ -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