[tip: x86/core] x86/hweight: Use ASM_CALL_CONSTRAINT in inline asm()

[tip-bot2 for Uros Bizjak]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     194a613088a8c9dae300dfb08433287cee803e8d
Gitweb:        https://git.kernel.org/tip/194a613088a8c9dae300dfb08433287cee803e8d
Author:        Uros Bizjak <ubizjak@xxxxxxxxx>
AuthorDate:    Wed, 12 Mar 2025 13:38:44 +01:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 19 Mar 2025 11:26:58 +01:00

x86/hweight: Use ASM_CALL_CONSTRAINT in inline asm()

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@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250312123905.149298-2-ubizjak@xxxxxxxxx
---
 arch/x86/include/asm/arch_hweight.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/arch_hweight.h b/arch/x86/include/asm/arch_hweight.h
index a11bb84..f233eb0 100644
--- a/arch/x86/include/asm/arch_hweight.h
+++ b/arch/x86/include/asm/arch_hweight.h
@@ -17,7 +17,7 @@ static __always_inline unsigned int __arch_hweight32(unsigned int w)
 	unsigned int res;
 
 	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));
 
 	return res;
@@ -45,7 +45,7 @@ static __always_inline unsigned long __arch_hweight64(__u64 w)
 	unsigned long res;
 
 	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));
 
 	return res;