Re: [PATCH] kbuild: Add $(KBUILD_HOSTLDFLAGS) to 'has_libelf' test

From: Masahiro Yamada <masahiroy@kernel.org>
To: Nathan Chancellor <nathan@kernel.org>
Cc: Michal Marek <michal.lkml@markovi.net>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH] kbuild: Add $(KBUILD_HOSTLDFLAGS) to 'has_libelf' test
Date: Sun, 25 Apr 2021 06:13:13 +0900	[thread overview]
Message-ID: <CAK7LNATgbzTBCrDaD3HhUQv=W3wLOKq3_iOiKM3CNEB4B=qh6Q@mail.gmail.com> (raw)
In-Reply-To: <20210422201914.3682494-1-nathan@kernel.org>

On Fri, Apr 23, 2021 at 5:19 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> Normally, invocations of $(HOSTCC) include $(KBUILD_HOSTLDFLAGS), which
> in turn includes $(HOSTLDFLAGS), which allows users to pass in their own
> flags when linking. However, the 'has_libelf' test does not, meaning
> that if a user requests a specific linker via HOSTLDFLAGS=-fuse-ld=...,
> it is not respected and the build might error.
>
> For example, if a user building with clang wants to use all of the LLVM
> tools without any GNU tools, they might remove all of the GNU tools from
> their system or PATH then build with
>
> $ make HOSTLDFLAGS=-fuse-ld=lld LLVM=1 LLVM_IAS=1
>
> which says use all of the LLVM tools, the integrated assembler, and
> ld.lld for linking host executables. Without this change, the build will
> error because $(HOSTCC) uses its default linker, rather than the one
> requested via -fuse-ld=..., which is GNU ld in clang's case in a default
> configuration.
>
> error: Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please
> install libelf-dev, libelf-devel or elfutils-libelf-devel
> make[1]: *** [Makefile:1260: prepare-objtool] Error 1
>
> Add $(KBUILD_HOSTLDFLAGS) to the 'has_libelf' test so that the linker
> choice is respected.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/479
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---

I applied this since the MW is opening shortly.

However, I believe the right thing to do is
to kill the pointless check entirely.

>  Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index bc19584fee59..1535b32c8baa 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1092,7 +1092,7 @@ export mod_sign_cmd
>  HOST_LIBELF_LIBS = $(shell pkg-config libelf --libs 2>/dev/null || echo -lelf)
>
>  has_libelf = $(call try-run,\
> -               echo "int main() {}" | $(HOSTCC) -xc -o /dev/null $(HOST_LIBELF_LIBS) -,1,0)
> +               echo "int main() {}" | $(HOSTCC) $(KBUILD_HOSTLDFLAGS) -xc -o /dev/null $(HOST_LIBELF_LIBS) -,1,0)
>
>  ifdef CONFIG_STACK_VALIDATION
>    ifeq ($(has_libelf),1)
>
> base-commit: bf05bf16c76bb44ab5156223e1e58e26dfe30a88
> --
> 2.31.1.362.g311531c9de
>

-- 
Best Regards
Masahiro Yamada