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

On Fri, Jun 12, 2026 at 6:31 AM Petr Pavlu <[email protected]> wrote:
>
> 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 <[email protected]>

Reviewed-by: Peter Collingbourne <[email protected]>

> ---
>  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
>