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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 30 Mar 2020 11:58:19 -0700
Message-ID: <CAKwvOd=5AG1ARw6JUXmkuiftuShuYHKLk0ZnueuLhvOdMr5dOA@mail.gmail.com>
Subject: Re: [PATCH v2] Makefile.llvm: simplify LLVM build
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     Nathan Chancellor <natechancellor@gmail.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Sandeep Patil <sspatil@google.com>
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On Sat, Mar 28, 2020 at 6:57 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> I also had planned to provide a single switch to change
> all the tool defaults to LLVM.
>
> So, supporting 'LLVM' is fine, but I'd rather want this
> look symmetrical, and easy to understand.
>
> CPP        = $(CC) -E
> ifneq ($(LLVM),)

Yes, a simple if statement is much simpler than the overly complex patch I had.

> CC         = $(LLVM_DIR)clang

Do we need $LLVM_DIR? Shouldn't users just have that in their $PATH?

Also, I think we need to support suffixed binaries, as debian
distributes these with version suffixes, as Nathan points out.  Or do
the debian packages install suffixed binaries AND path versioned
non-suffixed binaries?

> LD         = $(LLVM_DIR)ld.lld
> AR         = $(LLVM_DIR)llvm-ar
> NM         = $(LLVM_DIR)llvm-nm
> OBJCOPY    = $(LLVM_DIR)llvm-objcopy
> OBJDUMP    = $(LLVM_DIR)llvm-objdump
> READELF    = $(LLVM_DIR)llvm-readelf
> OBJSIZE    = $(LLVM_DIR)llvm-size
> STRIP      = $(LLVM_DIR)llvm-strip
> else
> CC         = $(CROSS_COMPILE)gcc
> LD         = $(CROSS_COMPILE)ld
> AR         = $(CROSS_COMPILE)ar
> NM         = $(CROSS_COMPILE)nm
> OBJCOPY    = $(CROSS_COMPILE)objcopy
> OBJDUMP    = $(CROSS_COMPILE)objdump
> READELF    = $(CROSS_COMPILE)readelf
> OBJSIZE    = $(CROSS_COMPILE)size
> STRIP      = $(CROSS_COMPILE)strip
> endif
>
>
>
> I attached two patches.
> Comments appreciated.

I'm not sure the second one that recommends changing cc/c++ is the way
to go; I think it might harm hermeticity.

> If you are so addicted to LLVM

Lol, maybe?
-- 
Thanks,
~Nick Desaulniers