linux-kernel - Re: [PATCH] x86: fix clang integrated assembler build

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Date:   Mon, 1 Jun 2020 14:04:34 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Bill Wendling <morbo@...gle.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        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>,
        "# 3.4.x" <stable@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Jiri Slaby <jslaby@...e.cz>,
        Juergen Gross <jgross@...e.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Tony Luck <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Fangrui Song <maskray@...gle.com>,
        Jian Cai <jiancai@...gle.com>
Subject: Re: [PATCH] x86: fix clang integrated assembler build

On Wed, May 27, 2020 at 1:57 PM Bill Wendling <morbo@...gle.com> wrote:
>
>
>
> On Wed, May 27, 2020 at 11:04 AM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>>
>> On Wed, May 27, 2020 at 7:16 AM Arnd Bergmann <arnd@...db.de> wrote:
>> >
>> > clang and gas seem to interpret the symbols in memmove_64.S and
>> > memset_64.S differently, such that clang does not make them
>> > 'weak' as expected, which leads to a linker error, with both
>> > ld.bfd and ld.lld:
>> >
>> > ld.lld: error: duplicate symbol: memmove
>> > >>> defined at common.c
>> > >>>            kasan/common.o:(memmove) in archive mm/built-in.a
>> > >>> defined at memmove.o:(__memmove) in archive arch/arm64/lib/lib.a
>> >
>> > ld.lld: error: duplicate symbol: memset
>> > >>> defined at common.c
>> > >>>            kasan/common.o:(memset) in archive mm/built-in.a
>> > >>> defined at memset.o:(__memset) in archive arch/arm64/lib/lib.a
>> >
>> > Copy the exact way these are written in memcpy_64.S, which does
>> > not have the same problem.
>> >
>> > I don't know why this makes a difference, and it would be good
>> > to have someone with a better understanding of assembler internals
>> > review it.
>> >
>> > It might be either a bug in the kernel or a bug in the assembler,
>> > no idea which one. My patch makes it work with all versions of
>> > clang and gcc, which is probably helpful even if it's a workaround
>> > for a clang bug.
>> >
>> > Cc: stable@...r.kernel.org
>> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>
>> + Bill, Fangrui, Jian
>> I think we saw this bug or a very similar bug internally around the
>> ordering of .weak to .global.
>>
> I think that would be this patch by Fangrui:
>
>   https://prodkernel-review.git.corp.google.com/c/kernel/release/9xx/+/292011

Thanks. That patch references this discussion:
https://lore.kernel.org/linuxppc-dev/20200325164257.170229-1-maskray@google.com/

>
> -bw
>
>>
>> > ---
>> >  arch/x86/lib/memmove_64.S | 4 ++--
>> >  arch/x86/lib/memset_64.S  | 4 ++--
>> >  2 files changed, 4 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/arch/x86/lib/memmove_64.S b/arch/x86/lib/memmove_64.S
>> > index 7ff00ea64e4f..dcca01434be8 100644
>> > --- a/arch/x86/lib/memmove_64.S
>> > +++ b/arch/x86/lib/memmove_64.S
>> > @@ -26,8 +26,8 @@
>> >   */
>> >  .weak memmove
>> >
>> > -SYM_FUNC_START_ALIAS(memmove)
>> > -SYM_FUNC_START(__memmove)
>> > +SYM_FUNC_START_ALIAS(__memmove)
>> > +SYM_FUNC_START_LOCAL(memmove)
>> >
>> >         mov %rdi, %rax
>> >
>> > diff --git a/arch/x86/lib/memset_64.S b/arch/x86/lib/memset_64.S
>> > index 9ff15ee404a4..a97f2ea4e0b2 100644
>> > --- a/arch/x86/lib/memset_64.S
>> > +++ b/arch/x86/lib/memset_64.S
>> > @@ -19,8 +19,8 @@
>> >   *
>> >   * rax   original destination
>> >   */
>> > -SYM_FUNC_START_ALIAS(memset)
>> > -SYM_FUNC_START(__memset)
>> > +SYM_FUNC_START_ALIAS(__memset)
>> > +SYM_FUNC_START_LOCAL(memset)
>> >         /*
>> >          * Some CPUs support enhanced REP MOVSB/STOSB feature. It is recommended
>> >          * to use it when possible. If not available, use fast string instructions.
>> > --
>> > 2.26.2
>> >
>> > --
>> > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
>> > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@...glegroups.com.
>> > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20200527141553.1768675-1-arnd%40arndb.de.
>>
>>
>>
>> --
>> Thanks,
>> ~Nick Desaulniers



-- 
Thanks,
~Nick Desaulniers