Re: [PATCH v2 05/11] x86/stackprotector/64: Convert stack protector to normal percpu variable

Brian Gerst
2023-10-29T07:15:53Z

On Sat, Oct 28, 2023 at 9:26 PM kernel test robot <lkp@intel.com> wrote:
>
> Hi Brian,
>
> kernel test robot noticed the following build errors:
>
> [auto build test ERROR on tip/master]
> [also build test ERROR on next-20231027]
> [cannot apply to tip/x86/core dennis-percpu/for-next linus/master tip/auto-latest v6.6-rc7]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>
> url: https://github.com/intel-lab-lkp/linux/commits/Brian-Gerst/x86-stackprotector-32-Remove-stack-protector-test-script/20231027-000533
> base: tip/master
> patch link: https://lore.kernel.org/r/20231026160100.195099-6-brgerst%40gmail.com
> patch subject: [PATCH v2 05/11] x86/stackprotector/64: Convert stack protector to normal percpu variable
> config: x86_64-rhel-8.3-rust (https://download.01.org/0day-ci/archive/20231029/202310290927.2MuJJdu9-lkp@intel.com/config)
> compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231029/202310290927.2MuJJdu9-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202310290927.2MuJJdu9-lkp@intel.com/
>
> All errors (new ones prefixed by >>):
>
> >> Unsupported relocation type: unknown type rel type name (42)

Clang is generating a new relocation type (R_X86_64_REX_GOTPCRELX)
that the relocs tool doesn't know about. This is supposed to allow
movq __stack_chk_guard@GOTPCREL(%rip), %rax
movq %gs:(%rax), %rax
to be relaxed to
leaq __stack_chk_guard(%rip), %rax
movq %gs:(%rax), %rax

But why is clang doing this instead of what GCC does?
movq %gs:__stack_chk_guard(%rip), %rax

Brian Gerst