linux-kernel - Re: [PATCH v2 01/39] kbuild: Fix clang build

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Date:   Wed, 2 Mar 2022 14:15:45 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     keescook@...omium.org, x86@...nel.org, joao@...rdrivepizza.com,
        hjl.tools@...il.com, jpoimboe@...hat.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com, mbenes@...e.cz, rostedt@...dmis.org,
        mhiramat@...nel.org, alexei.starovoitov@...il.com,
        Masahiro Yamada <masahiroy@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v2 01/39] kbuild: Fix clang build

On Wed, Mar 02, 2022 at 11:18:07AM -0800, Nick Desaulniers wrote:
> On Wed, Mar 2, 2022 at 8:37 AM Nathan Chancellor <nathan@...nel.org> wrote:
> >
> > On Tue, Mar 01, 2022 at 01:16:04PM -0800, Nick Desaulniers wrote:
> > > As per our previous discussion
> > > https://lore.kernel.org/linux-kbuild/CAKwvOd=x9E=7WcCiieso-CDiiU-wMFcXL4W3V5j8dq7BL5QT+w@mail.gmail.com/
> > > I'm still of the opionion that this should be solved by modifications
> > > (permanent or one off) to one's $PATH.
> >
> > However, I think we could still address Peter's complaint of "there
> > should be an easier way for me to use the tools that are already in my
> > PATH" with his first iteration of this patch [1], which I feel is
> > totally reasonable:
> >
> > $ make LLVM=-14
> >
> > It is still easy to use (in fact, it is shorter than 'CC=clang-14') and
> > it does not change anything else about how we build with LLVM. We would
> > just have to add something along the lines of
> >
> > "If your LLVM tools have a suffix like Debian's (clang-14, ld.lld-14,
> > etc.), use LLVM=<suffix>.
> 
> "If your LLVM tools have a suffix and you prefer to test an explicit
> version rather than the unsuffixed executables ..."

Ack, I included this.

> > $ make LLVM=-14"
> >
> > to Documentation/kbuild/llvm.rst.
> >
> > I might change the patch not to be so clever though:
> >
> > ifneq ($(LLVM),)
> > ifneq ($(LLVM),1)
> > LLVM_SFX := $(LLVM)
> > endif
> > endif
> >
> > [1]: https://lore.kernel.org/r/YXqpFHeY26sEbort@hirez.programming.kicks-ass.net/
> 
> I'd be much more amenable to that approach.

Sounds good, tentative patch attached, it passes all of my testing.
There is an instance of $(LLVM) in tools/testing/selftests/lib.mk that I
did not touch, as that will presumably have to go through the selftests
tree. I can send a separate patch for that later.

Peter, is this approach okay with you? If so, would you like to be
co-author or should I use a suggested-by tag?

Cheers,
Nathan

View attachment "0001-kbuild-Allow-a-suffix-with-LLVM.patch" of type "text/plain" (4677 bytes)