linux-kernel - Re: [PATCH v2] kbuild: Make $(LLVM) more flexible

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Message-ID: <YieGARVP2dhn8tbQ@casper.infradead.org>
Date:   Tue, 8 Mar 2022 16:36:17 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <shuah@...nel.org>, llvm@...ts.linux.dev,
        linux-kbuild@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2] kbuild: Make $(LLVM) more flexible

On Mon, Mar 07, 2022 at 11:08:29AM -0800, Nick Desaulniers wrote:
> > +``LLVM=0`` is not the same as omitting ``LLVM`` altogether, it will behave like
> > +``LLVM=1``.
> 
> Hmm... I can see someone's build wrappers setting LLVM=1, then them
> being surprised that appending LLVM=0 doesn't disable LLVM=1 as they
> might expect.  But Masahiro says let's fix this later which is fine.

What happens if you say LLVM= instead of LLVM=0 ?  Would that "undo"
a prior LLVM=1 and use GCC instead?