linux-kernel - [PATCH v2] codetag: Avoid unused alloc

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Message-ID: <20250618125037.53182-1-petr.pavlu@suse.com>
Date: Wed, 18 Jun 2025 14:50:35 +0200
From: Petr Pavlu <petr.pavlu@...e.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Arnd Bergmann <arnd@...db.de>,
	Casey Chen <cachen@...estorage.com>,
	linux-arch@...r.kernel.org,
	linux-modules@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Petr Pavlu <petr.pavlu@...e.com>
Subject: [PATCH v2] codetag: Avoid unused alloc_tags sections/symbols

With CONFIG_MEM_ALLOC_PROFILING=n, vmlinux and all modules unnecessarily
contain the symbols __start_alloc_tags and __stop_alloc_tags, which define
an empty range. In the case of modules, the presence of these symbols also
forces the linker to create an empty .codetag.alloc_tags section.

Update codetag.lds.h to make the data conditional on
CONFIG_MEM_ALLOC_PROFILING.

Signed-off-by: Petr Pavlu <petr.pavlu@...e.com>
Reviewed-by: Kent Overstreet <kent.overstreet@...ux.dev>
Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
---

Changes since v1 [1]:
- Trivially rebased the patch on top of "alloc_tag: remove empty module tag
  section" [2].

[1] https://lore.kernel.org/all/20250313143002.9118-1-petr.pavlu@suse.com/
[2] https://lore.kernel.org/all/20250610162258.324645-1-cachen@purestorage.com/

 include/asm-generic/codetag.lds.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/codetag.lds.h b/include/asm-generic/codetag.lds.h
index a45fe3d141a1..a14f4bdafdda 100644
--- a/include/asm-generic/codetag.lds.h
+++ b/include/asm-generic/codetag.lds.h
@@ -2,6 +2,12 @@
 #ifndef __ASM_GENERIC_CODETAG_LDS_H
 #define __ASM_GENERIC_CODETAG_LDS_H
 
+#ifdef CONFIG_MEM_ALLOC_PROFILING
+#define IF_MEM_ALLOC_PROFILING(...) __VA_ARGS__
+#else
+#define IF_MEM_ALLOC_PROFILING(...)
+#endif
+
 #define SECTION_WITH_BOUNDARIES(_name)	\
 	. = ALIGN(8);			\
 	__start_##_name = .;		\
@@ -9,7 +15,7 @@
 	__stop_##_name = .;
 
 #define CODETAG_SECTIONS()		\
-	SECTION_WITH_BOUNDARIES(alloc_tags)
+	IF_MEM_ALLOC_PROFILING(SECTION_WITH_BOUNDARIES(alloc_tags))
 
 #define MOD_SEPARATE_CODETAG_SECTION(_name)	\
 	.codetag.##_name : {			\
@@ -22,6 +28,6 @@
  * unload them individually once unused.
  */
 #define MOD_SEPARATE_CODETAG_SECTIONS()		\
-	MOD_SEPARATE_CODETAG_SECTION(alloc_tags)
+	IF_MEM_ALLOC_PROFILING(MOD_SEPARATE_CODETAG_SECTION(alloc_tags))
 
 #endif /* __ASM_GENERIC_CODETAG_LDS_H */

base-commit: 52da431bf03b5506203bca27fe14a97895c80faf
prerequisite-patch-id: acb6e2f6708cd75488806308bfecf682b2367dc9
-- 
2.49.0