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

Nathan Chancellor
2020-04-19T18:17:20Z

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.

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