Re: [PATCH] powerpc/vdso32: mark __kernel_datapage_offset as STV_PROTECTED

[Christophe Leroy]

Le 05/02/2020 Ã 01:50, Fangrui Song a ÃcritÂ:
> A PC-relative relocation (R_PPC_REL16_LO in this case) referencing a
> preemptible symbol in a -shared link is not allowed.  GNU ld's powerpc
> port is permissive and allows it [1], but lld will report an error after
> https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?id=ec0895f08f99515194e9fcfe1338becf6f759d38

Note that there is a series whose first two patches aim at dropping 
__kernel_datapage_offset . See 
https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=156045 
and especially patches https://patchwork.ozlabs.org/patch/1231467/ and 
https://patchwork.ozlabs.org/patch/1231461/

Those patches can be applied independentely of the rest.

Christophe

> Make the symbol protected so that it is non-preemptible but still
> exported.
>
> [1]: https://sourceware.org/bugzilla/show_bug.cgi?id=25500
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/851
> Signed-off-by: Fangrui Song <maskray@xxxxxxxxxx>
> ---
>   arch/powerpc/kernel/vdso32/datapage.S | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/vdso32/datapage.S b/arch/powerpc/kernel/vdso32/datapage.S
> index 217bb630f8f9..2831a8676365 100644
> --- a/arch/powerpc/kernel/vdso32/datapage.S
> +++ b/arch/powerpc/kernel/vdso32/datapage.S
> @@ -13,7 +13,8 @@
>   #include <asm/vdso_datapage.h>
>   
>   	.text
> -	.global	__kernel_datapage_offset;
> +	.global	__kernel_datapage_offset
> +	.protected	__kernel_datapage_offset
>   __kernel_datapage_offset:
>   	.long	0
>