Re: [PATCH 00/22] add support for Clang LTO

Sedat Dilek
2020-07-14T12:36:27Z

On Tue, Jul 14, 2020 at 2:16 PM Paul Menzel <pmenzel@molgen.mpg.de> wrote:
>
> Dear Sami,
>
>
> Am 13.07.20 um 01:34 schrieb Sami Tolvanen:
> > On Sat, Jul 11, 2020 at 9:32 AM Paul Menzel <pmenzel@molgen.mpg.de> wrote:
> >> Thank you very much for sending these changes.
> >>
> >> Do you have a branch, where your current work can be pulled from? Your
> >> branch on GitHub [1] seems 15 months old.
> >
> > The clang-lto branch is rebased regularly on top of Linus' tree.
> > GitHub just looks at the commit date of the last commit in the tree,
> > which isn't all that informative.
>
> Thank you for clearing this up, and sorry for not checking myself.
>
> >> Out of curiosity, I applied the changes, allowed the selection for i386
> >> (x86), and with Clang 1:11~++20200701093119+ffee8040534-1~exp1 from
> >> Debian experimental, it failed with `Invalid absolute R_386_32
> >> relocation: KERNEL_PAGES`:
> >
> > I haven't looked at getting this to work on i386, which is why we only
> > select ARCH_SUPPORTS_LTO for x86_64. I would expect there to be a few
> > issues to address.
> >
> >>> arch/x86/tools/relocs vmlinux > arch/x86/boot/compressed/vmlinux.relocs;arch/x86/tools/relocs --abs-relocs vmlinux
> >>> Invalid absolute R_386_32 relocation: KERNEL_PAGES
> >
> > KERNEL_PAGES looks like a constant, so it's probably safe to ignore
> > the absolute relocation in tools/relocs.c.
>
> Thank you for pointing me to the right direction. I am happy to report,
> that with the diff below (no idea to what list to add the string), Linux
> 5.8-rc5 with the LLVM/Clang/LTO patches on top, builds and boots on the
> ASRock E350M1.
>
> ```
> diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
> index 8f3bf34840cef..e91af127ed3c0 100644
> --- a/arch/x86/tools/relocs.c
> +++ b/arch/x86/tools/relocs.c
> @@ -79,6 +79,7 @@ static const char * const
> sym_regex_kernel[S_NSYMTYPES] = {
> "__end_rodata_hpage_align|"
> #endif
> "__vvar_page|"
> + "KERNEL_PAGES|"
> "_end)$"
> };
> ```
>

What llvm-toolchain and version did you use?

Can you post your linux-config?

Thanks.

- Sedat -