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Date: Thu, 2 Feb 2012 14:33:05 -0800
From: Josh Triplett <josh@...htriplett.org>
To: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Cc: Randy Dunlap <rdunlap@...otime.net>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Joe Perches <joe@...ches.com>
Subject: [PATCH] Documentation/CodingStyle: Add guidelines for inline assembly
Signed-off-by: Josh Triplett <josh@...htriplett.org>
---
Documentation/CodingStyle | 29 +++++++++++++++++++++++++++++
1 files changed, 29 insertions(+), 0 deletions(-)
diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle
index 2b90d32..c58b236 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
--
1.7.9
--
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