Re: [PATCH] x86/boot: allow a relocatable kernel to be linked with lld

[Fangrui Song]

On 2020-05-16, Dmitry Golovin wrote:
> 15.05.2020, 21:50, "Borislav Petkov" <bp@xxxxxxxxx>:
> > I need more info here about which segment is read-only?
> >
> > Is this something LLD does by default or what's happening?
>
> Probably should have quoted the original error message:
>
>    ld.lld: error: can't create dynamic relocation R_386_32 against
>    symbol: _bss in readonly segment; recompile object files with -fPIC
>    or pass '-Wl,-z,notext' to allow text relocations in the output

Do we know where do these R_386_32 come from?

When linking in -shared mode, the linker assumes the image is a shared
object and has undetermined image base at runtime. An absolute
relocation needs a text relocation (a relocation against a readonly
segment).

When neither -z notext nor -z text is specified, GNU ld is in an
indefinite state where it will enable text relocations (DT_TEXTREL
DF_TEXTREL) on demand. It is not considered a good practice for
userspace applications to do this.

Of course the kernel is different....... I know little about the kernel,
but if there is a way to make the sections containing R_386_32
relocations writable (SHF_WRITE), that will be a better solution to me.
In LLD, -z notext is like making every section SHF_WRITE.

> > IOW, don't be afraid to be more verbose in the commit message. :)
>
> Tried both BFD and LLD for linking to understand the difference more and
> rewrite the commit message, and came to the conclusion that the patch is
> wrong. I will submit v2 when I figure out the correct solution.
>
> Regards,
> Dmitry
>
> --
> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxxx
> To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/602331589572661%40mail.yandex.ru.