linux-kernel - Re: [PATCH v2] vmlinux.lds.h: Define SANTIZER_DISCARDS with CONFIG_GCOV

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Date:   Sat, 30 Jan 2021 01:39:28 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        kernel test robot <lkp@...el.com>,
        Fangrui Song <maskray@...gle.com>
Subject: Re: [PATCH v2] vmlinux.lds.h: Define SANTIZER_DISCARDS with CONFIG_GCOV_KERNEL=y

On Sat, Jan 30, 2021 at 1:27 AM Nathan Chancellor <nathan@...nel.org> 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>
> ---
>
> 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..0e6c5da667a7 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 unwanted sections

Typo: double "unwanted".

- Sedat -

> + * (.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
>
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