Re: [next] mips: clang-14-defconfig build regression

[Kees Cook <keescook@chromium.org>]

On Thu, Mar 03, 2022 at 10:05:22AM -0700, Nathan Chancellor wrote:
> Hi Naresh,
> 
> On Thu, Mar 03, 2022 at 09:09:56AM +0530, Naresh Kamboju wrote:
> > [Please ignore this email if it is already reported]
> > 
> > Linux next-20220302 mips builds failed [1] & [2].
> > 
> > Regressions found on mips:
> > 
> >   - mips-clang-12-defconfig
> >   - mips-clang-13-allnoconfig
> >   - mips-clang-12-allnoconfig
> >   - mips-clang-12-tinyconfig
> >   - mips-clang-13-defconfig
> >   - mips-clang-11-tinyconfig
> >   - mips-clang-11-defconfig
> >   - mips-clang-nightly-allnoconfig
> >   - mips-clang-14-tinyconfig
> >   - mips-clang-14-defconfig
> >   - mips-clang-11-allnoconfig
> >   - mips-clang-nightly-tinyconfig
> >   - mips-clang-13-tinyconfig
> >   - mips-clang-nightly-defconfig
> >   - mips-clang-14-allnoconfig
> > 
> > make --silent --keep-going --jobs=8
> > O=/home/tuxbuild/.cache/tuxmake/builds/1/build LLVM=1 LLVM_IAS=1
> > ARCH=mips CROSS_COMPILE=mips-linux-gnu- 'HOSTCC=sccache clang'
> > 'CC=sccache clang' defconfig
> 
> <snip>
> 
> > fatal error: error in backend: Invalid register name global variable
> 
> Thanks a lot for the report! Our CI caught this as well, I have filed an
> issue on our tracker and the upstream LLVM one:
> 
> https://github.com/ClangBuiltLinux/linux/issues/1608
> https://github.com/llvm/llvm-project/issues/54174
> 
> CC Kees, just as an FYI because of commit 200ed341b864 ("mips: Implement
> "current_stack_pointer"").

Oh! That's surprising. Thanks for digging out the details. The comment
in the code is amusing:

Register
MipsTargetLowering::getRegisterByName(const char *RegName, LLT VT,
                                      const MachineFunction &MF) const {
  // Named registers is expected to be fairly rare. For now, just support $28
  // since the linux kernel uses it.


Anyway, I guess I'll need to send a fix to make this compiler-version
dependent...

-- 
Kees Cook