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Date:   Wed, 2 Mar 2022 15:00:44 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        joao@overdrivepizza.com, hjl.tools@gmail.com, jpoimboe@redhat.com,
        andrew.cooper3@citrix.com, linux-kernel@vger.kernel.org,
        samitolvanen@google.com, mark.rutland@arm.com,
        alyssa.milburn@intel.com, mbenes@suse.cz, rostedt@goodmis.org,
        mhiramat@kernel.org, alexei.starovoitov@gmail.com,
        Masahiro Yamada <masahiroy@kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        llvm@lists.linux.dev
Subject: Re: [PATCH v2 01/39] kbuild: Fix clang build
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On Wed, Mar 02, 2022 at 02:15:45PM -0700, Nathan Chancellor wrote:
> 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.

I think it's fine to include that here, just to keep the logic together.

> 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

> From 83219caafbb7dbc2e41e3888ba5079d342aff633 Mon Sep 17 00:00:00 2001
> From: Nathan Chancellor <nathan@kernel.org>
> Date: Wed, 2 Mar 2022 13:28:14 -0700
> Subject: [PATCH] kbuild: Allow a suffix with $(LLVM)
> 
> The LLVM variable allows a developer to quickly switch between the GNU
> and LLVM tools. However, it does not handle versioned binaries, such as
> the ones shipped by Debian, as LLVM=1 just defines the build variables
> with the unversioned binaries.
> 
> There was some discussion during the review of the patch that introduces
> LLVM=1 around this, ultimately coming to the conclusion that developers
> can just add the folder that contains the unversioned binaries to their
> PATH, as Debian's versioned suffixed binaries are really just symlinks
> to the unversioned binaries in /usr/lib/llvm-#/bin:
> 
> $ realpath /usr/bin/clang-14
> /usr/lib/llvm-14/bin/clang
> 
> $ PATH=/usr/lib/llvm-14/bin:$PATH make ... LLVM=1
> 
> However, it is simple enough to support this scheme directly in the
> Kbuild system by allowing the developer to specify the version suffix
> with LLVM=, which is shorter than the above suggestion:
> 
> $ make ... LLVM=-14
> 
> It does not change the meaning of LLVM=1 (which will continue to use
> unversioned binaries) and it does not add too much additional complexity
> to the existing $(LLVM) code, while allowing developers to quickly test
> their series with different versions of the whole LLVM suite of tools.
> 
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

I like it!

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook