linux-kernel - [RFC 24/31] objtool: Make STACK_FRAME_NON

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Message-ID: <e06778646fdcf3013a6a64978971d88cfaafd35c.1725334260.git.jpoimboe@kernel.org>
Date: Mon,  2 Sep 2024 21:00:07 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: live-patching@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	x86@...nel.org,
	Miroslav Benes <mbenes@...e.cz>,
	Petr Mladek <pmladek@...e.com>,
	Joe Lawrence <joe.lawrence@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Marcos Paulo de Souza <mpdesouza@...e.com>,
	Song Liu <song@...nel.org>
Subject: [RFC 24/31] objtool: Make STACK_FRAME_NON_STANDARD consistent

The C version of STACK_FRAME_NON_STANDARD differs from its asm
counterpart:

- it uses an 8-byte entry (vs 4-byte)
- it creates a superfluous temporary variable

Make it identical to the asm version.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 include/linux/objtool.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/objtool.h b/include/linux/objtool.h
index b3b8d3dab52d..5e66b6d26df5 100644
--- a/include/linux/objtool.h
+++ b/include/linux/objtool.h
@@ -30,9 +30,10 @@
  *
  * For more information, see tools/objtool/Documentation/objtool.txt.
  */
-#define STACK_FRAME_NON_STANDARD(func) \
-	static void __used __section(".discard.func_stack_frame_non_standard") \
-		*__func_stack_frame_non_standard_##func = func
+#define STACK_FRAME_NON_STANDARD(func)						\
+	asm(".pushsection .discard.func_stack_frame_non_standard, \"aw\"\n\t"	\
+	    ".long " __stringify(func) " - .\n\t"						\
+	    ".popsection")
 
 /*
  * STACK_FRAME_NON_STANDARD_FP() is a frame-pointer-specific function ignore
-- 
2.45.2