Re: [PATCH] arm64: fix clang integrated assembler build

[Fangrui Song]

On 2020-05-27, 'Nick Desaulniers' via Clang Built Linux wrote:
> On Wed, May 27, 2020 at 7:14 AM Arnd Bergmann <arnd@xxxxxxxx> wrote:
> > clang and gas seem to interpret the symbols in memmove.S and
> > memset.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.
>
> + Bill, Fangrui, Jian
> I think we saw this bug or a very similar bug internally around the
> ordering of .weak to .global.

This may be another instance of
https://sourceware.org/pipermail/binutils/2020-March/000299.html
https://lore.kernel.org/linuxppc-dev/20200325164257.170229-1-maskray@xxxxxxxxxx/

I haven't checked but there may be both a .globl directive and a .weak
directive

> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > ---
> > ---
> >  arch/arm64/lib/memcpy.S  | 3 +--
> >  arch/arm64/lib/memmove.S | 3 +--
> >  arch/arm64/lib/memset.S  | 3 +--
> >  3 files changed, 3 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/arm64/lib/memcpy.S b/arch/arm64/lib/memcpy.S
> > index e0bf83d556f2..dc8d2a216a6e 100644
> > --- a/arch/arm64/lib/memcpy.S
> > +++ b/arch/arm64/lib/memcpy.S
> > @@ -56,9 +56,8 @@
> >         stp \reg1, \reg2, [\ptr], \val
> >         .endm
> >
> > -       .weak memcpy
> >  SYM_FUNC_START_ALIAS(__memcpy)
> > -SYM_FUNC_START_PI(memcpy)
> > +SYM_FUNC_START_WEAK_PI(memcpy)
> >  #include "copy_template.S"
> >         ret
> >  SYM_FUNC_END_PI(memcpy)
> > diff --git a/arch/arm64/lib/memmove.S b/arch/arm64/lib/memmove.S
> > index 02cda2e33bde..1035dce4bdaf 100644
> > --- a/arch/arm64/lib/memmove.S
> > +++ b/arch/arm64/lib/memmove.S
> > @@ -45,9 +45,8 @@ C_h   .req    x12
> >  D_l    .req    x13
> >  D_h    .req    x14
> >
> > -       .weak memmove
> >  SYM_FUNC_START_ALIAS(__memmove)
> > -SYM_FUNC_START_PI(memmove)
> > +SYM_FUNC_START_WEAK_PI(memmove)
> >         cmp     dstin, src
> >         b.lo    __memcpy
> >         add     tmp1, src, count
> > diff --git a/arch/arm64/lib/memset.S b/arch/arm64/lib/memset.S
> > index 77c3c7ba0084..a9c1c9a01ea9 100644
> > --- a/arch/arm64/lib/memset.S
> > +++ b/arch/arm64/lib/memset.S
> > @@ -42,9 +42,8 @@ dst           .req    x8
> >  tmp3w          .req    w9
> >  tmp3           .req    x9
> >
> > -       .weak memset
> >  SYM_FUNC_START_ALIAS(__memset)
> > -SYM_FUNC_START_PI(memset)
> > +SYM_FUNC_START_WEAK_PI(memset)
> >         mov     dst, dstin      /* Preserve return value.  */
> >         and     A_lw, val, #255
> >         orr     A_lw, A_lw, A_lw, lsl #8
> > --
> > 2.26.2
>
> --
> Thanks,
> ~Nick Desaulniers
>
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