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compiler-types.h: add asm_inline definition

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This adds an asm_inline macro which expands to "asm inline" [1] when
the compiler supports it. This is currently gcc 9.1+, gcc 8.3
and (once released) gcc 7.5 [2]. It expands to just "asm" for other
compilers.

Using asm inline("foo") instead of asm("foo") overrules gcc's
heuristic estimate of the size of the code represented by the asm()
statement, and makes gcc use the minimum possible size instead. That
can in turn affect gcc's inlining decisions.

I wasn't sure whether to make this a function-like macro or not - this
way, it can be combined with volatile as

  asm_inline volatile()

but perhaps we'd prefer to spell that

  asm_inline_volatile()

anyway.

The Kconfig logic is taken from an RFC patch by Masahiro Yamada [3].

[1] Technically, asm __inline, since both inline and __inline__
are macros that attach various attributes, making gcc barf if one
literally does "asm inline()". However, the third spelling __inline is
available for referring to the bare keyword.

[2] https://lore.kernel.org/lkml/20190907001411.GG9749@gate.crashing.org/

[3] https://lore.kernel.org/lkml/1544695154-15250-1-git-send-email-yamada.masahiro@socionext.com/

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
This commit is contained in:
Rasmus Villemoes 2019-09-13 00:19:25 +02:00 committed by Miguel Ojeda
parent c30724e9a0
commit eb11186930
2 changed files with 9 additions and 0 deletions
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6
include/linux/compiler_types.h
View File

@ -198,6 +198,12 @@ struct ftrace_likely_data {
#define asm_volatile_goto(x...) asm goto(x) #define asm_volatile_goto(x...) asm goto(x)
#endif #endif
#ifdef CONFIG_CC_HAS_ASM_INLINE
#define asm_inline asm __inline
#else
#define asm_inline asm
#endif
#ifndef __no_fgcse #ifndef __no_fgcse
# define __no_fgcse # define __no_fgcse
#endif #endif

3
init/Kconfig
View File

@ -30,6 +30,9 @@ config CC_CAN_LINK
config CC_HAS_ASM_GOTO config CC_HAS_ASM_GOTO
def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC)) def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
config CC_HAS_ASM_INLINE
def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
config CC_HAS_WARN_MAYBE_UNINITIALIZED config CC_HAS_WARN_MAYBE_UNINITIALIZED
def_bool $(cc-option,-Wmaybe-uninitialized) def_bool $(cc-option,-Wmaybe-uninitialized)
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