linux-kernel - Re: [PATCH v3] Makefile: use -z pack-relative-relocs

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Message-ID: <20230413145508.GC26421@willie-the-truck>
Date:   Thu, 13 Apr 2023 15:55:09 +0100
From:   Will Deacon <will@...nel.org>
To:     Fangrui Song <maskray@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Collingbourne <pcc@...gle.com>
Subject: Re: [PATCH v3] Makefile: use -z pack-relative-relocs

On Tue, Apr 11, 2023 at 08:09:44PM +0000, Fangrui Song wrote:
> Commit 27f2a4db76e8 ("Makefile: fix GDB warning with CONFIG_RELR")
> added --use-android-relr-tags to fix a GDB warning
> 
> BFD: /android0/linux-next/vmlinux: unknown type [0x13] section `.relr.dyn'
> 
> The GDB warning has been fixed in version 11.2.
> 
> The DT_ANDROID_RELR tag was deprecated since DT_RELR was standardized.
> Thus, --use-android-relr-tags should be removed. While making the
> change, try -z pack-relative-relocs, which is supported since LLD 15.
> Keep supporting --pack-dyn-relocs=relr as well for older LLD versions.
> There is no indication of obsolescence for --pack-dyn-relocs=relr.
> 
> As of today, GNU ld supports the latter option for x86 and powerpc64
> ports and has no intention to support --pack-dyn-relocs=relr. In the
> absence of the glibc symbol version GLIBC_ABI_DT_RELR,
> --pack-dyn-relocs=relr and -z pack-relative-relocs are identical in
> ld.lld.
> 
> GNU ld and newer versions of LLD report warnings (instead of errors) for
> unknown -z options. Only errors lead to non-zero exit codes. Therefore,
> we should test --pack-dyn-relocs=relr before testing
> -z pack-relative-relocs.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1057
> Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=a619b58721f0a03fd91c27670d3e4c2fb0d88f1e
> Signed-off-by: Fangrui Song <maskray@...gle.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
>  Makefile                      | 3 ++-
>  scripts/tools-support-relr.sh | 8 ++++++--
>  2 files changed, 8 insertions(+), 3 deletions(-)

Acked-by: Will Deacon <will@...nel.org>

Masahiro -- are you happy to pick this one up? If not, I can take it via
arm64 (as the only arch currently using this reloc format).

Cheers,

Will