linux-kernel - Re: [PATCH 2/2] kbuild: Disable CONFIG_LD_ORPHAN

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Message-ID: <CAKwvOdni24b_70xm+xK_7r2N77WrsOk4_OgoLiwSzZ5f+6vqfA@mail.gmail.com>
Date:   Tue, 17 Nov 2020 11:41:15 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Kees Cook <keescook@...omium.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "kernelci . org bot" <bot@...nelci.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH 2/2] kbuild: Disable CONFIG_LD_ORPHAN_WARN for ld.lld 10.0.1

On Fri, Nov 13, 2020 at 11:56 AM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> ld.lld 10.0.1 spews a bunch of various warnings about .rela sections,
> along with a few others. Newer versions of ld.lld do not have these
> warnings. As a result, do not add '--orphan-handling=warn' to
> LDFLAGS_vmlinux if ld.lld's version is not new enough.
>
> Reported-by: Arvind Sankar <nivedita@...m.mit.edu>
> Reported-by: kernelci.org bot <bot@...nelci.org>
> Reported-by: Mark Brown <broonie@...nel.org>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1187
> Link: https://github.com/ClangBuiltLinux/linux/issues/1193
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  MAINTAINERS            |  1 +
>  init/Kconfig           |  6 +++++-
>  scripts/lld-version.sh | 20 ++++++++++++++++++++
>  3 files changed, 26 insertions(+), 1 deletion(-)
>  create mode 100755 scripts/lld-version.sh
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 3da6d8c154e4..4b83d3591ec7 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4284,6 +4284,7 @@ B:        https://github.com/ClangBuiltLinux/linux/issues
>  C:     irc://chat.freenode.net/clangbuiltlinux
>  F:     Documentation/kbuild/llvm.rst
>  F:     scripts/clang-tools/
> +F:     scripts/lld-version.sh
>  K:     \b(?i:clang|llvm)\b
>
>  CLEANCACHE API
> diff --git a/init/Kconfig b/init/Kconfig
> index a270716562de..40c9ca60ac1d 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -47,6 +47,10 @@ config CLANG_VERSION
>         int
>         default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
>
> +config LLD_VERSION
> +       int
> +       default $(shell,$(srctree)/scripts/lld-version.sh $(LD))
> +
>  config CC_CAN_LINK
>         bool
>         default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT
> @@ -1349,7 +1353,7 @@ config LD_DEAD_CODE_DATA_ELIMINATION
>           own risk.
>
>  config LD_ORPHAN_WARN
> -       def_bool ARCH_WANT_LD_ORPHAN_WARN && $(ld-option,--orphan-handling=warn)
> +       def_bool ARCH_WANT_LD_ORPHAN_WARN && $(ld-option,--orphan-handling=warn) && (!LD_IS_LLD || LLD_VERSION >= 110000)
>
>  config SYSCTL
>         bool
> diff --git a/scripts/lld-version.sh b/scripts/lld-version.sh
> new file mode 100755
> index 000000000000..cc779f412e39
> --- /dev/null
> +++ b/scripts/lld-version.sh
> @@ -0,0 +1,20 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# ld.lld-version ld.lld-command

^ it looks like this format was copied from scripts/gcc-version, but
it's kind of curious/cryptic to me for a comment about usage.  Is it
necessary?  A comment in the form:

# Usage: ./scripts/lld-version.sh ld.lld

Would be clearer to me.

> +#
> +# Print the linker version of `ld.lld-command' in a 5 or 6-digit form
> +# such as `100001' for ld.lld 10.0.1 etc.
> +
> +linker="$*"
> +
> +if ! ( $linker --version | grep -q LLD ); then
> +       echo 0
> +       exit 1
> +fi
> +
> +VERSION=$($linker --version | cut -d ' ' -f 2)

This is going to invoke the linker potentially twice if it's LLD.
Would it be nicer to capture the output of `$linker --version`, check
which linker it is, then slice that up via `cut` to get the version?

This version is fine to me, but if you're going to send a v2, that
might be a nice slight cleanup.  Otherwise,

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>

(Please drop those tags if you modify this for v2 and I'll rereview/retest).

> +MAJOR=$(echo $VERSION | cut -d . -f 1)
> +MINOR=$(echo $VERSION | cut -d . -f 2)
> +PATCHLEVEL=$(echo $VERSION | cut -d . -f 3)
> +printf "%d%02d%02d\\n" $MAJOR $MINOR $PATCHLEVEL
> --
> 2.29.2
>


-- 
Thanks,
~Nick Desaulniers