[PATCH] ARM: Make UNWINDER_ARM depend on ld.bfd or ld.lld 11.0.0+

[Nick Desaulniers]

On Wed, Mar 10, 2021 at 4:54 PM Nathan Chancellor <nathan at kernel.org> wrote:
>
> When linking aspeed_g5_defconfig with ld.lld 10.0.1, the following error
> occurs:
>
> ld.lld: error: .tmp_vmlinux.kallsyms1:(.ARM.exidx+0x34D98): relocation
> R_ARM_PREL31 out of range: 2135538592 is not in [-1073741824,
> 1073741823]
>
> This was resolved in ld.lld 11.0.0 but the minimum supported version of
> ld.lld for the kernel is 10.0.1. Prevent CONFIG_UNWINDER_ARM from being
> selected in this case so that the problematic sections cannot be
> created.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/732
> Link: https://github.com/llvm/llvm-project/commit/48aebfc908ba7b9372aaa478a9c200789491096e
> Suggested-by: Nick Desaulniers <ndesaulniers at google.com>
> Signed-off-by: Nathan Chancellor <nathan at kernel.org>

Thanks for the patch.  We discussed at the kernelCI meeting yesterday
and the clangbuiltlinux meeting today continuing coverage for kernel
builds with clang-10, so this is still worthwhile IMO at least for
randconfig testing not to select known broken configs when using older
tools. We can rip it out once we bump the minimum supported version of
clang.

Reviewed-by: Nick Desaulniers <ndesaulniers at google.com>

> ---
>  arch/arm/Kconfig.debug | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
> index 9e0b5e7f12af..64c1f8a46ab5 100644
> --- a/arch/arm/Kconfig.debug
> +++ b/arch/arm/Kconfig.debug
> @@ -66,6 +66,8 @@ config UNWINDER_FRAME_POINTER
>  config UNWINDER_ARM
>         bool "ARM EABI stack unwinder"
>         depends on AEABI && !FUNCTION_GRAPH_TRACER
> +       # https://github.com/ClangBuiltLinux/linux/issues/732
> +       depends on !LD_IS_LLD || LLD_VERSION >= 110000
>         select ARM_UNWIND
>         help
>           This option enables stack unwinding support in the kernel
>
> base-commit: a38fd8748464831584a19438cbb3082b5a2dab15
> --

-- 
Thanks,
~Nick Desaulniers