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

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Message-ID: <20200419181715.GA36234@ubuntu-s3-xlarge-x86>
Date:   Sun, 19 Apr 2020 11:17:15 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com, linux-kbuild@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Dmitry Golovin <dima@...ovin.in>,
        Sedat Dilek <sedat.dilek@...il.com>
Subject: Re: [PATCH 2/2] MIPS: VDSO: Do not disable VDSO when linking with
 ld.lld

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@...ovin.in>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.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.

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