linux-kernel - Re: [PATCH v3] vmlinux.lds.h: Define SANTIZER_DISCARDS with CONFIG_GCOV

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Date:   Thu, 25 Feb 2021 12:28:21 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        kernel test robot <lkp@...el.com>,
        Fangrui Song <maskray@...gle.com>
Subject: Re: [PATCH v3] vmlinux.lds.h: Define SANTIZER_DISCARDS with
 CONFIG_GCOV_KERNEL=y

On Fri, Jan 29, 2021 at 05:46:51PM -0700, Nathan Chancellor wrote:
> clang produces .eh_frame sections when CONFIG_GCOV_KERNEL is enabled,
> even when -fno-asynchronous-unwind-tables is in KBUILD_CFLAGS:
> 
> $ make CC=clang vmlinux
> ...
> ld: warning: orphan section `.eh_frame' from `init/main.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/version.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/do_mounts.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/do_mounts_initrd.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/initramfs.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/calibrate.o' being placed in section `.eh_frame'
> ld: warning: orphan section `.eh_frame' from `init/init_task.o' being placed in section `.eh_frame'
> ...
> 
> $ rg "GCOV_KERNEL|GCOV_PROFILE_ALL" .config
> CONFIG_GCOV_KERNEL=y
> CONFIG_ARCH_HAS_GCOV_PROFILE_ALL=y
> CONFIG_GCOV_PROFILE_ALL=y
> 
> This was already handled for a couple of other options in
> commit d812db78288d ("vmlinux.lds.h: Avoid KASAN and KCSAN's unwanted
> sections") and there is an open LLVM bug for this issue. Take advantage
> of that section for this config as well so that there are no more orphan
> warnings.
> 
> Link: https://bugs.llvm.org/show_bug.cgi?id=46478
> Link: https://github.com/ClangBuiltLinux/linux/issues/1069
> Reported-by: kernel test robot <lkp@...el.com>
> Reviewed-by: Fangrui Song <maskray@...gle.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
> 
> v2 -> v3:
> 
> * Fix double "unwanted" in comment section per Sedat.
> 
> v1 -> v2:
> 
> * Keep configs and flag names alphabetized.
> 
> * Drop mention of -ftest-coverage since it does not cause this issue per
>   Fangrui.
> 
> * Pick up review tags from Fangrui and Nick.
> 
>  include/asm-generic/vmlinux.lds.h | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index b2b3d81b1535..b61b537177fb 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -988,12 +988,13 @@
>  #endif
>  
>  /*
> - * Clang's -fsanitize=kernel-address and -fsanitize=thread produce
> - * unwanted sections (.eh_frame and .init_array.*), but
> - * CONFIG_CONSTRUCTORS wants to keep any .init_array.* sections.
> + * Clang's -fprofile-arcs, -fsanitize=kernel-address, and
> + * -fsanitize=thread produce unwanted sections (.eh_frame
> + * and .init_array.*), but CONFIG_CONSTRUCTORS wants to
> + * keep any .init_array.* sections.
>   * https://bugs.llvm.org/show_bug.cgi?id=46478
>   */
> -#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN)
> +#if defined(CONFIG_GCOV_KERNEL) || defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN)
>  # ifdef CONFIG_CONSTRUCTORS
>  #  define SANITIZER_DISCARDS						\
>  	*(.eh_frame)
> 
> base-commit: bec4c2968fce2f44ce62d05288a633cd99a722eb
> -- 
> 2.30.0
> 

Andrew, Arnd, or Kees:

Would one of you be able to pick this up and get it to Linus? I think
the 0day bot just tripped over this again:

https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org/message/BXBY7OPVMOCCUZSCFEZXI7RG65RJWJ52/
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org/message/QF62LWM6YSNWWNOM7AXYK4734AKH2SVT/

Cheers,
Nathan