Re: [PATCH 2/2] MIPS: VDSO: Do not disable VDSO when linking with ld.lld

From: Masahiro Yamada <masahiroy@kernel.org>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	linux-mips@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	Dmitry Golovin <dima@golovin.in>,
	Sedat Dilek <sedat.dilek@gmail.com>
Subject: Re: [PATCH 2/2] MIPS: VDSO: Do not disable VDSO when linking with ld.lld
Date: Mon, 20 Apr 2020 04:32:20 +0900	[thread overview]
Message-ID: <CAK7LNAS7QHB3GuBeLDh66OHbYRMzmNQNwiueU7jH1i7v0UTAAQ@mail.gmail.com> (raw)
In-Reply-To: <20200419181715.GA36234@ubuntu-s3-xlarge-x86>

On Mon, Apr 20, 2020 at 3:17 AM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> On Sun, Apr 19, 2020 at 11:04:45AM -0700, Nathan Chancellor wrote:
> > Currently, when linking with ld.lld, this warning pops up:
> >
> >     arch/mips/vdso/Makefile:70: MIPS VDSO requires binutils >= 2.25
> >
> > ld-ifversion calls ld-version, which calls scripts/ld-version.sh, which
> > is specific to GNU ld. ld.lld has a completely different versioning
> > scheme (as it follows LLVM's versioning) and it does not have the issue
> > mentioned in the comment above this block so it should not be subjected
> > to this check.
> >
> > With this patch, the VDSO successfully links and shows P_MIPS_PC32 in
> > vgettimeofday.o.
> >
> > $ llvm-objdump -Dr arch/mips/vdso/vgettimeofday.o | grep R_MIPS_PC32
> >                       00000024:  R_MIPS_PC32  _start
> >                       000000b0:  R_MIPS_PC32  _start
> >                       000002bc:  R_MIPS_PC32  _start
> >                       0000036c:  R_MIPS_PC32  _start
> >                       00000468:  R_MIPS_PC32  _start
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/785
> > Link: https://github.com/llvm/llvm-project/commit/e364e2e9ce50c12eb2bf093560e1a1a8544d455a
> > Reported-by: Dmitry Golovin <dima@golovin.in>
> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > ---
> >  arch/mips/vdso/Makefile | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> > index d7fe8408603e..f99e583d14a1 100644
> > --- a/arch/mips/vdso/Makefile
> > +++ b/arch/mips/vdso/Makefile
> > @@ -65,9 +65,11 @@ DISABLE_VDSO := n
> >  # the comments on that file.
> >  #
> >  ifndef CONFIG_CPU_MIPSR6
> > -  ifeq ($(call ld-ifversion, -lt, 225000000, y),y)
> > -    $(warning MIPS VDSO requires binutils >= 2.25)
> > -    DISABLE_VDSO := y
> > +  ifndef CONFIG_LD_IS_LLD
> > +    ifeq ($(call ld-ifversion, -lt, 225000000, y),y)
> > +      $(warning MIPS VDSO requires binutils >= 2.25)
> > +      DISABLE_VDSO := y
> > +    endif
> >    endif
> >  endif
> >
> > --
> > 2.26.1
> >
>
> Hmmm, I still see this warning when first runing make <config>... I
> assume because this Makefile gets parsed before Kconfig runs.

I do not see the warning for 'make <config>'.

Could you tell me how to reproduce it?

For cleaning, indeed, i see the warning.

$ make ARCH=mips  LLVM=1 clean
arch/mips/vdso/Makefile:70: MIPS VDSO requires binutils >= 2.25

>
> Perhaps it would be better to check if ld-version is 0 (since that means
> we are not using GNU ld):
>
> ifneq ($(call ld-ifversion, -eq, 0, y),y)
>
> I am open to suggestions though.
>
> Cheers,
> Nathan
>
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-- 
Best Regards
Masahiro Yamada