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x86/hweight: Use ASM_CALL_CONSTRAINT in inline asm()

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Use ASM_CALL_CONSTRAINT to prevent inline asm() that includes call
instruction from being scheduled before the frame pointer gets set
up by the containing function. This unconstrained scheduling might
cause objtool to print a "call without frame pointer save/setup"
warning. Current versions of compilers don't seem to trigger this
condition, but without this constraint there's nothing to prevent
the compiler from scheduling the insn in front of frame creation.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250312123905.149298-2-ubizjak@gmail.com
This commit is contained in:
Uros Bizjak 2025-03-12 13:38:44 +01:00 • committed by Ingo Molnar
parent 72899899e4
commit 194a613088
1 changed files with 2 additions and 2 deletions
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4
arch/x86/include/asm/arch_hweight.h
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@ -17,7 +17,7 @@ static __always_inline unsigned int __arch_hweight32(unsigned int w)
unsigned int res; unsigned int res;
asm (ALTERNATIVE("call __sw_hweight32", "popcntl %[val], %[cnt]", X86_FEATURE_POPCNT) asm (ALTERNATIVE("call __sw_hweight32", "popcntl %[val], %[cnt]", X86_FEATURE_POPCNT)
: [cnt] "=" REG_OUT (res) : [cnt] "=" REG_OUT (res), ASM_CALL_CONSTRAINT
: [val] REG_IN (w)); : [val] REG_IN (w));
return res; return res;
@ -45,7 +45,7 @@ static __always_inline unsigned long __arch_hweight64(__u64 w)
unsigned long res; unsigned long res;
asm (ALTERNATIVE("call __sw_hweight64", "popcntq %[val], %[cnt]", X86_FEATURE_POPCNT) asm (ALTERNATIVE("call __sw_hweight64", "popcntq %[val], %[cnt]", X86_FEATURE_POPCNT)
: [cnt] "=" REG_OUT (res) : [cnt] "=" REG_OUT (res), ASM_CALL_CONSTRAINT
: [val] REG_IN (w)); : [val] REG_IN (w));
return res; return res;