Re: [PATCH v8 00/16] Add support for Clang LTO

[Sami Tolvanen <samitolvanen@google.com>]

On Sat, Dec 5, 2020 at 10:50 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> On Fri, Dec 04, 2020 at 02:52:41PM -0800, Sami Tolvanen wrote:
> > On Thu, Dec 3, 2020 at 2:32 PM Nick Desaulniers <ndesaulniers@google.com> wrote:
> > >
> > > So I'd recommend to Sami to simply make the Kconfig also depend on
> > > clang's integrated assembler (not just llvm-nm and llvm-ar).
> >
> > Sure, sounds good to me. What's the preferred way to test for this in Kconfig?
> >
> > It looks like actually trying to test if we have an LLVM assembler
> > (e.g. using $(as-instr,.section
> > ".linker-options","e",@llvm_linker_options)) doesn't work as Kconfig
> > doesn't pass -no-integrated-as to clang here.

After a closer look, that's actually not correct, this seems to work
with Clang+LLD no matter which assembler is used. I suppose we could
test for .gasversion. to detect GNU as, but that's hardly ideal.

> >I could do something
> > simple like $(success,echo $(LLVM) $(LLVM_IAS) | grep -q "1 1").
> >
> > Thoughts?
> >
> > Sami
>
> I think
>
>     depends on $(success,test $(LLVM_IAS) -eq 1)
>
> should work, at least according to my brief test.

Sure, looks good to me. However, I think we should also test for
LLVM=1 to avoid possible further issues with mismatched toolchains
instead of only checking for llvm-nm and llvm-ar.

Sami