Re: [PATCH v3] kbuild: Strip runtime const RELA sections correctly

[Masahiro Yamada]

On Tue, Jan 14, 2025 at 12:53 AM Ard Biesheuvel <ardb+git@xxxxxxxxxx> wrote:
>
> From: Ard Biesheuvel <ardb@xxxxxxxxxx>
>
> Due to the fact that runtime const ELF sections are named without a
> leading period or double underscore, the RSTRIP logic that removes the
> static RELA sections from vmlinux fails to identify them.


Dumb question - why can't you rename the section 'runtime*' to '.runtime*' ?

.rel* matches to sections that just happen to start with '.rel',
which may not be REL or RELA.





> This results
> in a situation like below, where some sections that were supposed to get
> removed are left behind.
>
>   [Nr] Name                              Type            Address          Off     Size   ES Flg Lk Inf Al
>
>   [58] runtime_shift_d_hash_shift        PROGBITS        ffffffff83500f50 2900f50 000014 00   A  0   0  1
>   [59] .relaruntime_shift_d_hash_shift   RELA            0000000000000000 55b6f00 000078 18   I 70  58  8
>   [60] runtime_ptr_dentry_hashtable      PROGBITS        ffffffff83500f68 2900f68 000014 00   A  0   0  1
>   [61] .relaruntime_ptr_dentry_hashtable RELA            0000000000000000 55b6f78 000078 18   I 70  60  8
>   [62] runtime_ptr_USER_PTR_MAX          PROGBITS        ffffffff83500f80 2900f80 000238 00   A  0   0  1
>   [63] .relaruntime_ptr_USER_PTR_MAX     RELA            0000000000000000 55b6ff0 000d50 18   I 70  62  8
>
> So tweak the match expression to strip all sections starting with .rel.
> While at it, consolidate the logic used by RISC-V, s390 and x86 into a
> single shared Makefile library command.
>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx
> Cc: linux-s390@xxxxxxxxxxxxxxx
> Cc: Ron Economos <re@xxxxxxxx>
> Link: https://lore.kernel.org/all/CAHk-=wjk3ynjomNvFN8jf9A1k=qSc=JFF591W00uXj-qqNUxPQ@xxxxxxxxxxxxxx/
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> ---
> v3: put back missing 'endif' to fix the RISC-V build
> v2: add missing include of scripts/Makefile.lib
>
>  arch/riscv/Makefile.postlink |  8 ++------
>  arch/s390/Makefile.postlink  |  6 +-----
>  arch/x86/Makefile.postlink   |  6 +-----
>  scripts/Makefile.lib         |  3 +++
>  4 files changed, 7 insertions(+), 18 deletions(-)
>
> diff --git a/arch/riscv/Makefile.postlink b/arch/riscv/Makefile.postlink
> index 829b9abc91f6..750d2784f69e 100644
> --- a/arch/riscv/Makefile.postlink
> +++ b/arch/riscv/Makefile.postlink
> @@ -10,6 +10,7 @@ __archpost:
>
>  -include include/config/auto.conf
>  include $(srctree)/scripts/Kbuild.include
> +include $(srctree)/scripts/Makefile.lib
>
>  quiet_cmd_relocs_check = CHKREL  $@
>  cmd_relocs_check =                                                     \
> @@ -19,11 +20,6 @@ ifdef CONFIG_RELOCATABLE
>  quiet_cmd_cp_vmlinux_relocs = CPREL   vmlinux.relocs
>  cmd_cp_vmlinux_relocs = cp vmlinux vmlinux.relocs
>
> -quiet_cmd_relocs_strip = STRIPREL $@
> -cmd_relocs_strip = $(OBJCOPY)   --remove-section='.rel.*'       \
> -                                --remove-section='.rel__*'      \
> -                                --remove-section='.rela.*'      \
> -                                --remove-section='.rela__*' $@
>  endif
>
>  # `@true` prevents complaint when there is nothing to be done
> @@ -33,7 +27,7 @@ vmlinux: FORCE
>  ifdef CONFIG_RELOCATABLE
>         $(call if_changed,relocs_check)
>         $(call if_changed,cp_vmlinux_relocs)
> -       $(call if_changed,relocs_strip)
> +       $(call if_changed,strip_relocs)
>  endif
>
>  clean:
> diff --git a/arch/s390/Makefile.postlink b/arch/s390/Makefile.postlink
> index df82f5410769..1ae5478cd6ac 100644
> --- a/arch/s390/Makefile.postlink
> +++ b/arch/s390/Makefile.postlink
> @@ -11,6 +11,7 @@ __archpost:
>
>  -include include/config/auto.conf
>  include $(srctree)/scripts/Kbuild.include
> +include $(srctree)/scripts/Makefile.lib
>
>  CMD_RELOCS=arch/s390/tools/relocs
>  OUT_RELOCS = arch/s390/boot
> @@ -19,11 +20,6 @@ quiet_cmd_relocs = RELOCS  $(OUT_RELOCS)/relocs.S
>         mkdir -p $(OUT_RELOCS); \
>         $(CMD_RELOCS) $@ > $(OUT_RELOCS)/relocs.S
>
> -quiet_cmd_strip_relocs = RSTRIP  $@
> -      cmd_strip_relocs = \
> -       $(OBJCOPY) --remove-section='.rel.*' --remove-section='.rel__*' \
> -                  --remove-section='.rela.*' --remove-section='.rela__*' $@
> -
>  vmlinux: FORCE
>         $(call cmd,relocs)
>         $(call cmd,strip_relocs)
> diff --git a/arch/x86/Makefile.postlink b/arch/x86/Makefile.postlink
> index fef2e977cc7d..8b8a68162c94 100644
> --- a/arch/x86/Makefile.postlink
> +++ b/arch/x86/Makefile.postlink
> @@ -11,6 +11,7 @@ __archpost:
>
>  -include include/config/auto.conf
>  include $(srctree)/scripts/Kbuild.include
> +include $(srctree)/scripts/Makefile.lib
>
>  CMD_RELOCS = arch/x86/tools/relocs
>  OUT_RELOCS = arch/x86/boot/compressed
> @@ -20,11 +21,6 @@ quiet_cmd_relocs = RELOCS  $(OUT_RELOCS)/$@.relocs
>         $(CMD_RELOCS) $@ > $(OUT_RELOCS)/$@.relocs; \
>         $(CMD_RELOCS) --abs-relocs $@
>
> -quiet_cmd_strip_relocs = RSTRIP  $@
> -      cmd_strip_relocs = \
> -       $(OBJCOPY) --remove-section='.rel.*' --remove-section='.rel__*' \
> -                  --remove-section='.rela.*' --remove-section='.rela__*' $@
> -
>  # `@true` prevents complaint when there is nothing to be done
>
>  vmlinux: FORCE
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 7395200538da..f604f51d23ca 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -374,6 +374,9 @@ quiet_cmd_ar = AR      $@
>  quiet_cmd_objcopy = OBJCOPY $@
>  cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@
>
> +quiet_cmd_strip_relocs = RSTRIP  $@
> +cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel*' $@
> +
>  # Gzip
>  # ---------------------------------------------------------------------------
>
> --
> 2.47.1.688.g23fc6f90ad-goog
>


-- 
Best Regards
Masahiro Yamada