Commit-ID: ae37a8cd9b0ad3416d71e54cfaeb3744178189a8 Gitweb: https://git.kernel.org/tip/ae37a8cd9b0ad3416d71e54cfaeb3744178189a8 Author: Borislav Petkov <b...@suse.de> AuthorDate: Thu, 7 Mar 2019 15:54:51 +0100 Committer: Borislav Petkov <b...@suse.de> CommitDate: Fri, 29 Mar 2019 19:13:48 +0100
x86/cpufeature: Remove __pure attribute to _static_cpu_has() __pure is used to make gcc do Common Subexpression Elimination (CSE) and thus save subsequent invocations of a function which does a complex computation (without side effects). As a simple example: bool a = _static_cpu_has(x); bool b = _static_cpu_has(x); gets turned into bool a = _static_cpu_has(x); bool b = a; However, gcc doesn't do CSE with asm()s when those get inlined - like it is done with _static_cpu_has() - because, for example, the t_yes/t_no labels are different for each inlined function body and thus cannot be detected as equivalent anymore for the CSE heuristic to hit. However, this all is beside the point because best it should be avoided to have more than one call to _static_cpu_has(X) in the same function due to the fact that each such call is an alternatives patch site and it is simply pointless. Therefore, drop the __pure attribute as it is not doing anything. Reported-by: Nadav Amit <nadav.a...@gmail.com> Signed-off-by: Borislav Petkov <b...@suse.de> Cc: Peter Zijlstra <pet...@infradead.org> Cc: x...@kernel.org Link: https://lkml.kernel.org/r/20190307151036.gd26...@zn.tnic --- arch/x86/include/asm/cpufeature.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index ce95b8cbd229..2fb791a1b479 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -159,7 +159,7 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit); * These will statically patch the target code for additional * performance. */ -static __always_inline __pure bool _static_cpu_has(u16 bit) +static __always_inline bool _static_cpu_has(u16 bit) { asm_volatile_goto("1: jmp 6f\n" "2:\n"
