linux-kernel - [PATCH v2] objtool, x86/hweight: Remove ANNOTATE_IGNORE

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Message-ID: <e7070dba3278c90f1a836b16157dcd34ccd21e21.1744318586.git.jpoimboe@kernel.org>
Date: Thu, 10 Apr 2025 13:58:35 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v2] objtool, x86/hweight: Remove ANNOTATE_IGNORE_ALTERNATIVE

Since objtool's inception, frame pointer warnings have been manually
silenced for __arch_hweight*() to allow those functions' inline asm to
avoid using ASM_CALL_CONSTRAINT.

The potentially dubious reasoning for that decision over nine years ago
was that since !X86_FEATURE_POPCNT is exceedingly rare, it's not worth
hurting the code layout for a function call that will never happen on
the vast majority of systems.

However, those functions actually started using ASM_CALL_CONSTRAINT with
the following commit:

  194a613088a8 ("x86/hweight: Use ASM_CALL_CONSTRAINT in inline asm()")

And rightfully so, as it makes the code correct.  ASM_CALL_CONSTRAINT
will soon have no effect for non-FP configs anyway.

With ASM_CALL_CONSTRAINT in place, ANNOTATE_IGNORE_ALTERNATIVE no longer
has a purpose for the hweight functions.  Remove it.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---

This was originally posted with the RFC series:

  https://lore.kernel.org/cover.1744098446.git.jpoimboe@kernel.org

But it's actually a standalone patch which can be merged independently.

 arch/x86/include/asm/arch_hweight.h | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/arch_hweight.h b/arch/x86/include/asm/arch_hweight.h
index cbc6157f0b4b..b5982b94bdba 100644
--- a/arch/x86/include/asm/arch_hweight.h
+++ b/arch/x86/include/asm/arch_hweight.h
@@ -16,8 +16,7 @@ static __always_inline unsigned int __arch_hweight32(unsigned int w)
 {
 	unsigned int res;

-	asm_inline (ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE
-				"call __sw_hweight32",
+	asm_inline (ALTERNATIVE("call __sw_hweight32",
 				"popcntl %[val], %[cnt]", X86_FEATURE_POPCNT)
 			 : [cnt] "=" REG_OUT (res), ASM_CALL_CONSTRAINT
 			 : [val] REG_IN (w));
@@ -46,8 +45,7 @@ static __always_inline unsigned long __arch_hweight64(__u64 w)
 {
 	unsigned long res;

-	asm_inline (ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE
-				"call __sw_hweight64",
+	asm_inline (ALTERNATIVE("call __sw_hweight64",
 				"popcntq %[val], %[cnt]", X86_FEATURE_POPCNT)
 			 : [cnt] "=" REG_OUT (res), ASM_CALL_CONSTRAINT
 			 : [val] REG_IN (w));
-- 
2.49.0