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Message-ID: <20210323190532.eiqxmskiankf7hn3@archlinux-ax161>
Date: Tue, 23 Mar 2021 12:05:32 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
clang-built-linux@...glegroups.com,
Fangrui Song <maskray@...gle.com>,
Elliot Berman <eberman@...cinc.com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Peter Collingbourne <pcc@...gle.com>,
Michal Marek <michal.lkml@...kovi.net>,
linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Makefile: fix GDB warning with CONFIG_RELR
On Thu, Mar 18, 2021 at 05:07:06PM -0700, Nick Desaulniers wrote:
> GDB produces the following warning when debugging kernels built with
> CONFIG_RELR:
>
> BFD: /android0/linux-next/vmlinux: unknown type [0x13] section `.relr.dyn'
>
> when loading a kernel built with CONFIG_RELR into GDB. It can also
> prevent debugging symbols using such relocations.
>
> Peter sugguests:
> [That flag] means that lld will use dynamic tags and section type
> numbers in the OS-specific range rather than the generic range. The
> kernel itself doesn't care about these numbers; it determines the
> location of the RELR section using symbols defined by a linker script.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1057
> Suggested-by: Peter Collingbourne <pcc@...gle.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> ---
> Makefile | 2 +-
> scripts/tools-support-relr.sh | 3 ++-
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 5160ff8903c1..47741cb60995 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1088,7 +1088,7 @@ LDFLAGS_vmlinux += $(call ld-option, -X,)
> endif
>
> ifeq ($(CONFIG_RELR),y)
> -LDFLAGS_vmlinux += --pack-dyn-relocs=relr
> +LDFLAGS_vmlinux += --pack-dyn-relocs=relr --use-android-relr-tags
> endif
>
> # We never want expected sections to be placed heuristically by the
> diff --git a/scripts/tools-support-relr.sh b/scripts/tools-support-relr.sh
> index 45e8aa360b45..cb55878bd5b8 100755
> --- a/scripts/tools-support-relr.sh
> +++ b/scripts/tools-support-relr.sh
> @@ -7,7 +7,8 @@ trap "rm -f $tmp_file.o $tmp_file $tmp_file.bin" EXIT
> cat << "END" | $CC -c -x c - -o $tmp_file.o >/dev/null 2>&1
> void *p = &p;
> END
> -$LD $tmp_file.o -shared -Bsymbolic --pack-dyn-relocs=relr -o $tmp_file
> +$LD $tmp_file.o -shared -Bsymbolic --pack-dyn-relocs=relr \
> + --use-android-relr-tags -o $tmp_file
>
> # Despite printing an error message, GNU nm still exits with exit code 0 if it
> # sees a relr section. So we need to check that nothing is printed to stderr.
> --
> 2.31.0.rc2.261.g7f71774620-goog
>
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