linux-kernel - [tip: x86/asm] x86/hweight: Use ASM_CALL

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Message-ID: <174180800206.14745.2087027613593191613.tip-bot2@tip-bot2>
Date: Wed, 12 Mar 2025 19:33:22 -0000
From: "tip-bot2 for Uros Bizjak" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>, Ingo Molnar <mingo@...nel.org>,
 "H. Peter Anvin" <hpa@...or.com>, Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/asm] x86/hweight: Use ASM_CALL_CONSTRAINT in inline asm()

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

Commit-ID:     01ba23bf1b3f9a4035faedc2aa450e251bcc2c7c
Gitweb:        https://git.kernel.org/tip/01ba23bf1b3f9a4035faedc2aa450e251bcc2c7c
Author:        Uros Bizjak <ubizjak@...il.com>
AuthorDate:    Wed, 12 Mar 2025 13:38:44 +01:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Wed, 12 Mar 2025 20:18:29 +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@...il.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: https://lore.kernel.org/r/20250312123905.149298-2-ubizjak@gmail.com
---
 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;