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From: Nathan Chancellor <natechancellor@gmail.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: yamada.masahiro@socionext.com, keescook@chromium.org,
	clang-built-linux@googlegroups.com,
	Michal Marek <michal.lkml@markovi.net>,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] Makefile: lld: tell clang to use lld
Date: Tue, 2 Apr 2019 00:27:26 -0700	[thread overview]
Message-ID: <20190402072726.GA16650@archlinux-ryzen> (raw)
In-Reply-To: <20190402070858.49597-1-ndesaulniers@google.com>

On Tue, Apr 02, 2019 at 12:08:58AM -0700, Nick Desaulniers wrote:
> This is needed because clang doesn't select which linker to use based on
> $LD but rather -fuse-ld={bfd,gold,lld,<absolute path to linker>}.  This
> is problematic especially for cc-ldoption, which checks for linker flag
> support via invoking the compiler, rather than the linker.
> 
> Select the linker via absolute path from $PATH via `which`. This allows
> you to build with:
> 
> $ make LD=ld.lld
> $ make LD=ld.lld-8
> $ make LD=/path/to/ld.lld
> 
> Add -Qunused-arguments to KBUILD_CPPFLAGS when using LLD, as otherwise
> Clang likes to complain about -fuse-lld= being unused when compiling but
> not linking (-c) such as when cc-option is used.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/342
> Link: https://github.com/ClangBuiltLinux/linux/issues/366
> Link: https://github.com/ClangBuiltLinux/linux/issues/357
> Suggested-by: Nathan Chancellor <natechancellor@gmail.com>
> Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> Changes V2->V3:
> * Use absolute path based on `which $LD` as per Masahiro.
> * Add -Qunused-arguments.
> * Drop tested-by/reviewed-by tags, since this patched has changed enough
>   to warrant re-testing/re-review, IMO.
> * Add more info to the commit message.
> Changes V1->V2:
> * add reviewed and tested by tags.
> * move this addition up 2 statments so that it's properly added to
>   KBUILD_*FLAGS as per Nathan.
> 
>  Makefile | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index 026fbc450906..895c076b6305 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -514,6 +514,10 @@ ifneq ($(GCC_TOOLCHAIN),)
>  CLANG_FLAGS	+= --gcc-toolchain=$(GCC_TOOLCHAIN)
>  endif
>  CLANG_FLAGS	+= -no-integrated-as
> +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),)
> +CLANG_FLAGS	+= -fuse-ld=$(shell which $(LD))
> +KBUILD_CPPFLAGS += -Qunused-arguments

We should remove the -Qunused-arguments call in the second clang block
at the same time. With that change:

Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>

> +endif
>  KBUILD_CFLAGS	+= $(CLANG_FLAGS)
>  KBUILD_AFLAGS	+= $(CLANG_FLAGS)
>  export CLANG_FLAGS
> -- 
> 2.21.0.392.gf8f6787159e-goog
> 

  reply	other threads:[~2019-04-02  7:27 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-11 19:30 [PATCH v2 1/4] init/Kconfig: add config support for detecting linker ndesaulniers
2019-02-11 19:30 ` [PATCH v2 2/4] Makefile: clang: choose GCC_TOOLCHAIN_DIR not on LD ndesaulniers
2019-02-16  3:02   ` Masahiro Yamada
2019-02-11 19:30 ` [PATCH v2 3/4] Makefile: lld: tell clang to use lld ndesaulniers
2019-02-13 14:58   ` Masahiro Yamada
2019-02-13 17:41     ` Nick Desaulniers
2019-02-16  3:07       ` Masahiro Yamada
2019-04-02  3:54         ` Nick Desaulniers
2019-04-02  4:49           ` Masahiro Yamada
2019-04-02  7:08             ` [PATCH v3] " Nick Desaulniers
2019-04-02  7:27               ` Nathan Chancellor [this message]
2019-04-02  7:33                 ` [PATCH v4] " Nick Desaulniers
2019-04-02  7:57                   ` Nathan Chancellor
2019-04-02  7:52               ` [PATCH v3] " Sedat Dilek
2019-04-02  7:56                 ` Nathan Chancellor
2019-04-05 10:16               ` Masahiro Yamada
2019-04-05 16:11                 ` Kees Cook
2019-04-05 16:52                   ` Nick Desaulniers
2019-04-07  2:20                     ` Masahiro Yamada
2019-02-11 19:30 ` [PATCH v2 4/4] Makefile: lld: set -O2 linker flag when linking with LLD ndesaulniers
2019-02-12 12:22   ` Peter Zijlstra
2019-02-16  2:55   ` Masahiro Yamada
2019-02-11 19:30 ` [PATCH v2 0/4] Improve kernel LLD support ndesaulniers

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