Re: [PATCH v1 1/2] LoongArch: Make LTO case independent in Makefile

[Tiezhu Yang]

On 9/20/25 19:41, Huacai Chen wrote:
...

> > > We need to handle the other case to use -fno-jump-tables if llvm does
> > > not support -loongarch-annotate-tablejump.
> > >
> > > So, it is better to update the minimal version of llvm to 20, which
> > > includes the following two important commits:
> > >
> > > [LoongArch] Add options for annotate tablejump
> > > https://github.com/llvm/llvm-project/commit/4c2c17756739
> > >
> > > [LoongArch] Avoid indirect branch jumps using the ra register
> > > https://github.com/llvm/llvm-project/commit/21ef17c62645
> > >
> > > If you are OK, I will send a patch to modify the following file:
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/min-tool-version.sh#n29
> > >
> > >
> > > and keep arch/loongarch/Makefile as is.
> >
> > The other way is to keep scripts/min-tool-version.sh as is, and only
> > modify arch/loongarch/Makefile, something like this (not tested):
> >
> > config LLD_HAS_ANNOTATE_TABLEJUMP
> >          def_bool LLD_VERSION >= 200000
> >
> > ifdef CONFIG_LTO_CLANG
> > ifdef CONFIG_LLD_HAS_ANNOTATE_TABLEJUMP
> > KBUILD_LDFLAGS                  += -mllvm --loongarch-annotate-tablejump
> > else
> > KBUILD_LDFLAGS                  += -mllvm --no-jump-tables
> > endif
> So complicated?
>
> I think below is enough, no?
> ifdef CONFIG_LTO_CLANG
> # The annotate-tablejump option can not be passed to LLVM backend when
> LTO is enabled.
> # Ensure it is aware of linker with LTO,
> '--loongarch-annotate-tablejump' also needs to
> # be passed via '-mllvm' to ld.lld.
> KBUILD_LDFLAGS                  += $(call ld-option,-mllvm
> --loongarch-annotate-tablejump,-mllvm --no-jump-tables)
> endif

I do not know whether this is valid, you can test it with llvm 18
and llvm 20 if you think it is a proper way.

But IIRC, there is objtool warning with llvm 18, I reported to llvm
developer Wang Lei and he fixed it as the following commit:

[LoongArch] Avoid indirect branch jumps using the ra register
https://github.com/llvm/llvm-project/commit/21ef17c62645

Actually, the above commit solved a performance issue of llvm compiler,
so I prefer to update the minimal llvm version to 20 for LoongArch.

Thanks,
Tiezhu