linux-kernel - [PATCH RFC 3/5] noinstr: Use asm_inline() in instrumentation

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Message-ID: <7cb41fe7e87a003fc925164d5cc18efd8e95fcc0.1744098446.git.jpoimboe@kernel.org>
Date: Tue,  8 Apr 2025 01:21:16 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH RFC 3/5] noinstr: Use asm_inline() in instrumentation_{begin,end}()

Use asm_inline() to prevent the compiler from making poor inlining
decisions based on the length of the objtool annotations.

For a defconfig kernel built with GCC 14.2.1, bloat-o-meter reports a
0.18% text size increase:

  add/remove: 88/433 grow/shrink: 967/487 up/down: 87579/-52630 (34949)
  Total: Before=19448407, After=19483356, chg +0.18%

Presumably the text growth is due to increased inlining.  A net total of
345 functions were removed.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 include/linux/instrumentation.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/instrumentation.h b/include/linux/instrumentation.h
index bf675a8aef8a..b1007407d272 100644
--- a/include/linux/instrumentation.h
+++ b/include/linux/instrumentation.h
@@ -9,7 +9,7 @@
 
 /* Begin/end of an instrumentation safe region */
 #define __instrumentation_begin(c) ({					\
-	asm volatile(__stringify(c) ": nop\n\t"				\
+	asm_inline volatile(__stringify(c) ": nop\n\t"			\
 		     ANNOTATE_INSTR_BEGIN(__ASM_BREF(c))		\
 		     : : "i" (c));					\
 })
@@ -47,7 +47,7 @@
  * part of the condition block and does not escape.
  */
 #define __instrumentation_end(c) ({					\
-	asm volatile(__stringify(c) ": nop\n\t"				\
+	asm_inline volatile(__stringify(c) ": nop\n\t"			\
 		     ANNOTATE_INSTR_END(__ASM_BREF(c))			\
 		     : : "i" (c));					\
 })
-- 
2.49.0