linux-kernel - Re: [RFC PATCH 0/6] linkage: better symbol aliasing

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Message-ID: <CAMj1kXHUtyn9K91jkqdU69-acvGkYsPZ-yeb7dALOeztDpfDvg@mail.gmail.com>
Date:   Mon, 6 Dec 2021 15:06:44 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Slaby <jslaby@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Brown <broonie@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <maz@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Fuad Tabba <tabba@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>
Subject: Re: [RFC PATCH 0/6] linkage: better symbol aliasing

On Mon, 6 Dec 2021 at 13:47, Mark Rutland <mark.rutland@....com> wrote:
>
> This series aims to make symbol aliasing simpler and more consistent.
> The basic idea is to replace SYM_FUNC_START_ALIAS(alias) and
> SYM_FUNC_END_ALIAS(alias) with a new SYM_FUNC_ALIAS(alias, name), so
> that e.g.
>
>     SYM_FUNC_START(func)
>     SYM_FUNC_START_ALIAS(alias1)
>     SYM_FUNC_START_ALIAS(alias2)
>         ... asm insns ...
>     SYM_FUNC_END(func)
>     SYM_FUNC_END_ALIAS(alias1)
>     SYM_FUNC_END_ALIAS(alias2)
>     EXPORT_SYMBOL(alias1)
>     EXPORT_SYMBOL(alias2)
>
> ... can become:
>
>     SYM_FUNC_START(name)
>         ... asm insns ...
>     SYM_FUNC_END(name)
>
>     SYM_FUNC_ALIAS(alias1, func)
>     EXPORT_SYMBOL(alias1)
>
>     SYM_FUNC_ALIAS(alias2, func)
>     EXPORT_SYMBOL(alias2)
>
> This avoids repetition and hopefully make it easier to ensure
> consistency (e.g. so each function has a single canonical name and
> associated metadata).
>
> I'm sending this as an RFC since I want to check:
>
> a) People are happy with the idea in principle.
>
> b) People are happy with the implementation within <linux/linkage.h>.
>
> ... and I haven't yet converted the headers under tools/, which is
> largely a copy+paste job.
>
> I've build+boot tested arm64 and x86 defconfig without issues, and I've
> pushed the series to my `linkage/alias-rework` branch on git.kernel.org,
> atop v5.16-rc3:
>
>   git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git linkage/alias-rework
>   https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=linkage/alias-rework
>
> Thanks,
> Mark.
>
> Mark Rutland (6):
>   linkage: add SYM_{ENTRY,START,END}_AT()
>   linkage: add SYM_FUNC_{LOCAL_,}ALIAS()
>   arm64: remove __dma_*_area() aliases
>   arm64: clean up symbol aliasing
>   x86: clean up symbol aliasing
>   linkage: remove START/END ALIAS macros
>

I never understood why we had these start/end markers in the first
place for alias definitions, so good riddance.

Acked-by: Ard Biesheuvel <ardb@...nel.org>


>  Documentation/asm-annotations.rst  | 11 ++--
>  arch/arm64/include/asm/linkage.h   | 24 ---------
>  arch/arm64/kvm/hyp/nvhe/cache.S    |  5 +-
>  arch/arm64/lib/clear_page.S        |  5 +-
>  arch/arm64/lib/copy_page.S         |  5 +-
>  arch/arm64/lib/memchr.S            |  5 +-
>  arch/arm64/lib/memcmp.S            |  6 +--
>  arch/arm64/lib/memcpy.S            | 21 ++++----
>  arch/arm64/lib/memset.S            | 12 +++--
>  arch/arm64/lib/strchr.S            |  6 ++-
>  arch/arm64/lib/strcmp.S            |  6 +--
>  arch/arm64/lib/strlen.S            |  6 +--
>  arch/arm64/lib/strncmp.S           |  8 +--
>  arch/arm64/lib/strnlen.S           |  6 ++-
>  arch/arm64/lib/strrchr.S           |  5 +-
>  arch/arm64/mm/cache.S              | 59 +++++++++-----------
>  arch/x86/boot/compressed/head_32.S |  3 +-
>  arch/x86/boot/compressed/head_64.S |  3 +-
>  arch/x86/lib/memcpy_64.S           | 10 ++--
>  arch/x86/lib/memmove_64.S          |  4 +-
>  arch/x86/lib/memset_64.S           |  6 +--
>  include/linux/linkage.h            | 86 ++++++++++++++++++------------
>  22 files changed, 146 insertions(+), 156 deletions(-)
>
> --
> 2.30.2
>