linux-kernel - Re: [PATCH 1/4] kbuild: remove LLVM=1 test from HAS_LTO

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Message-ID: <CAK7LNAQ4SibwSONO8io5_b1d-ELmfTYTpwfwJk=ABcfsNhEU3g@mail.gmail.com>
Date:   Fri, 5 Mar 2021 15:06:04 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Nathan Chancellor <nathan@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] kbuild: remove LLVM=1 test from HAS_LTO_CLANG

On Thu, Mar 4, 2021 at 5:47 AM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:
>
> + Sami
>
> On Wed, Mar 3, 2021 at 10:34 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > This guarding is wrong. As Documentation/kbuild/llvm.rst notes, LLVM=1
> > switches the default of tools, but you can still override CC, LD, etc.
> > individually.
> >
> > BTW, LLVM is not 1/0 flag. If LLVM is not passed in, it is empty.
>
> Do we have the same problem with LLVM_IAS?  LGTM otherwise, but wanted
> to check that before signing off.

3/4 will replace this LLVM_IAS check with AS_IS_LLVM.

We do not need to add a noise change.




>
> (Also, the rest of the patches in this series seem more related to
> DWARFv5 cleanups; this patch seems orthogonal while those are a
> visible progression).

Kind of orthogonal, but I am touching the same code hunk,
which would cause a merge conflict.


> >
> > Non-zero return code is all treated as failure anyway.
> >
> > So, $(success,test $(LLVM) -eq 1) and $(success,test "$(LLVM)" = 1)
> > works equivalently in the sense that both are expanded to 'n' if LLVM
> > is not given. The difference is that the former internally fails due
> > to syntax error.
> >
> >   $ test ${LLVM} -eq 1
> >   bash: test: -eq: unary operator expected
> >   $ echo $?
> >   2
> >
> >   $ test "${LLVM}" -eq 1
> >   bash: test: : integer expression expected
> >   $ echo $?
> >   2
> >
> >   $ test "${LLVM}" = 1
> >   echo $?
> >   1
> >
> >   $ test -n "${LLVM}"
> >   $ echo $?
> >   1
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
> >
> >  arch/Kconfig | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 2bb30673d8e6..2af10ebe5ed0 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -632,7 +632,6 @@ config HAS_LTO_CLANG
> >         def_bool y
> >         # Clang >= 11: https://github.com/ClangBuiltLinux/linux/issues/510
> >         depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD
> > -       depends on $(success,test $(LLVM) -eq 1)
>
> IIRC, we needed some other LLVM utilities like llvm-nm and llvm-ar,
> which are checked below. So I guess we can still support CC=clang
> AR=llvm-ar NM=llvm-nm, and this check is redundant.

Yes, I think so.


>
> >         depends on $(success,test $(LLVM_IAS) -eq 1)
> >         depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
> >         depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
> > --
> > 2.27.0
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers
>
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-- 
Best Regards
Masahiro Yamada