linux-kernel - Re: [PATCH] efi/libstub: refactor cmd

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Date:   Fri, 15 Feb 2019 14:48:43 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Alistair Strachan <astrachan@...gle.com>,
        Laura Abbott <labbott@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: Re: [PATCH] efi/libstub: refactor cmd_stubcopy

On Tue, Feb 12, 2019 at 4:26 PM Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
>
> On Tue, 12 Feb 2019 at 04:45, Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
> >
> > It took me a while to understand what is going on in the nested
> > if-blocks.
> >
> > Simplify it by removing unneeded code.
> >
> >   - if_changed automatically adds 'set -e', so any failure in the
> >     series of commands makes it immediately fail as a whole.
> >     So, the outer if block is entirely redundant.
> >
> >   - Since commit 9c2af1c7377a ("kbuild: add .DELETE_ON_ERROR special
> >     target"), GNU Make automatically deletes the target on any failure
> >     in its recipe. The explicit 'rm -f $@' is redundant.
> >
> >   - surrounding commands with ( ) will spawn a subshell to execute them
> >     in it, but it is rarely useful to do so.
> >
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>
> Assuming that it still works as expected:
>
> Acked-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>
> You can test this by adding a statically initialized global function
> pointer to any of the libstub source files that get built for ARM.
>
> Thanks!


I tried that, and it failed as expected.


$ git diff
diff --git a/drivers/firmware/efi/libstub/arm32-stub.c
b/drivers/firmware/efi/libstub/arm32-stub.c
index becbda4..5ad7bbd 100644
--- a/drivers/firmware/efi/libstub/arm32-stub.c
+++ b/drivers/firmware/efi/libstub/arm32-stub.c
@@ -28,6 +28,8 @@ efi_status_t
check_platform_features(efi_system_table_t *sys_table_arg)
        return EFI_SUCCESS;
 }

+void * foo = (void *)check_platform_features;
+
 static efi_guid_t screen_info_guid = LINUX_EFI_ARM_SCREEN_INFO_TABLE_GUID;

 struct screen_info *alloc_screen_info(efi_system_table_t *sys_table_arg)
$ make ARCH=arm  CROSS_COMPILE=arm-linux-gnueabihf- defconfig
drivers/firmware/efi/libstub/
*** Default configuration is based on 'multi_v7_defconfig'
#
# configuration written to .config
#
scripts/kconfig/conf  --syncconfig Kconfig
  CALL    scripts/checksyscalls.sh
  CC      drivers/firmware/efi/libstub/arm32-stub.o
  STUBCPY drivers/firmware/efi/libstub/arm32-stub.stub.o
00000000 R_ARM_ABS32       check_platform_features
drivers/firmware/efi/libstub/arm32-stub.stub.o: absolute symbol
references not allowed in the EFI stub
drivers/firmware/efi/libstub/Makefile:80: recipe for target
'drivers/firmware/efi/libstub/arm32-stub.stub.o' failed
make[3]: *** [drivers/firmware/efi/libstub/arm32-stub.stub.o] Error 1
make[3]: *** Deleting file 'drivers/firmware/efi/libstub/arm32-stub.stub.o'
Makefile:1705: recipe for target 'drivers/firmware/efi/libstub/' failed
make[2]: *** [drivers/firmware/efi/libstub/] Error 2
/home/masahiro/workspace/bsp/linux/Makefile:300: recipe for target
'__build_one_by_one' failed
make[1]: *** [__build_one_by_one] Error 2
Makefile:160: recipe for target 'sub-make' failed
make: *** [sub-make] Error 2





-- 
Best Regards
Masahiro Yamada