[PATCH] kbuild: Use --force-group-allocation when linking modules

[Petr Pavlu <petr.pavlu@suse.com>]

Specific code, such as outlined KASAN checks, may be placed in
COMDAT-deduplicated sections. When linking modules as relocatable files,
the linker by default preserves such groups, potentially leaving multiple
copies in the resulting modules and unnecessary group metadata.

Use --force-group-allocation to have the linker resolve the COMDAT groups
and place their members as regular sections. The option is available from
ld.bfd 2.29 and ld.lld 19.1.0.

Remove the workaround in arch/arm64/include/asm/module.lds.h that was added
for the same problem but limited to CONFIG_KASAN_SW_TAGS and .text.hot.
Note that this code currently has no effect anyway because all .text.hot
sections are placed in the .text output section by scripts/module.lds.S,
since commit 1ba9f8979426 ("vmlinux.lds: Unify TEXT_MAIN, DATA_MAIN, and
related macros").

Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
---
 Makefile                            |  6 ++++++
 arch/arm64/include/asm/module.lds.h | 13 -------------
 2 files changed, 6 insertions(+), 13 deletions(-)

diff --git a/Makefile b/Makefile
index e156e2696efe..1729af0690b3 100644
--- a/Makefile
+++ b/Makefile
@@ -1189,6 +1189,12 @@ KBUILD_RUSTFLAGS += $(KRUSTFLAGS)
 KBUILD_LDFLAGS_MODULE += --build-id=sha1
 LDFLAGS_vmlinux += --build-id=sha1
 
+# Specific code, such as outlined KASAN checks, may be placed in
+# COMDAT-deduplicated sections. Use --force-group-allocation to resolve these
+# groups when linking modules. The option is available from ld.bfd 2.29 and
+# ld.lld 19.1.0.
+KBUILD_LDFLAGS_MODULE += $(call ld-option,--force-group-allocation)
+
 KBUILD_LDFLAGS	+= -z noexecstack
 ifeq ($(CONFIG_LD_IS_BFD),y)
 KBUILD_LDFLAGS	+= $(call ld-option,--no-warn-rwx-segments)
diff --git a/arch/arm64/include/asm/module.lds.h b/arch/arm64/include/asm/module.lds.h
index fb944b46846d..792a0820757a 100644
--- a/arch/arm64/include/asm/module.lds.h
+++ b/arch/arm64/include/asm/module.lds.h
@@ -4,19 +4,6 @@ SECTIONS {
 	.text.ftrace_trampoline 0 : { BYTE(0) }
 	.init.text.ftrace_trampoline 0 : { BYTE(0) }
 
-#ifdef CONFIG_KASAN_SW_TAGS
-	/*
-	 * Outlined checks go into comdat-deduplicated sections named .text.hot.
-	 * Because they are in comdats they are not combined by the linker and
-	 * we otherwise end up with multiple sections with the same .text.hot
-	 * name in the .ko file. The kernel module loader warns if it sees
-	 * multiple sections with the same name so we use this sections
-	 * directive to force them into a single section and silence the
-	 * warning.
-	 */
-	.text.hot : { *(.text.hot) }
-#endif
-
 #ifdef CONFIG_UNWIND_TABLES
 	/*
 	 * Currently, we only use unwind info at module load time, so we can

base-commit: 4549871118cf616eecdd2d939f78e3b9e1dddc48
-- 
2.54.0