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

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Message-ID: <CAKwvOdkhZGv_q9vgDdYY44OrbzmMD_E+GL3SyOk-jQ0kdXtMzg@mail.gmail.com>
Date:   Wed, 3 Mar 2021 12:47:27 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>
Cc:     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

+ 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.

(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).

>
> 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.

>         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