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clang: work around asm output constraint problems

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Work around clang problems with "=rm" asm constraint.

clang seems to always chose the memory output, while it is almost
always the worst choice.

Add ASM_OUTPUT_RM so that we can replace "=rm" constraint
where it matters for clang, while not penalizing gcc.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eric Dumazet
2025-12-19 11:20:06 +00:00
committed by Linus Torvalds
parent f67e8a5e3e
commit 4cc5373f2e
2 changed files with 3 additions and 1 deletions
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1
include/linux/compiler-clang.h
View File

@@ -145,6 +145,7 @@
*/
#define ASM_INPUT_G "ir"
#define ASM_INPUT_RM "r"
#define ASM_OUTPUT_RM "=r"
/*
* Declare compiler support for __typeof_unqual__() operator.

3
include/linux/compiler_types.h
View File

@@ -548,11 +548,12 @@ struct ftrace_likely_data {
/*
* Clang has trouble with constraints with multiple
* alternative behaviors (mainly "g" and "rm").
* alternative behaviors ("g" , "rm" and "=rm").
*/
#ifndef ASM_INPUT_G
#define ASM_INPUT_G "g"
#define ASM_INPUT_RM "rm"
#define ASM_OUTPUT_RM "=rm"
#endif
#ifdef CONFIG_CC_HAS_ASM_INLINE