linux-kernel - Re: [PATCH] arm64: vdso32: Fix '--prefix=' value for newer versions of clang

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Message-ID: <20200723045145.GA448242@ubuntu-n2-xlarge-x86>
Date:   Wed, 22 Jul 2020 21:51:45 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Sedat Dilek <sedat.dilek@...il.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        stable@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [PATCH] arm64: vdso32: Fix '--prefix=' value for newer versions
 of clang

On Thu, Jul 23, 2020 at 06:45:07AM +0200, Sedat Dilek wrote:
> On Thu, Jul 23, 2020 at 6:15 AM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> >
> > Newer versions of clang only look for $(COMPAT_GCC_TOOLCHAIN_DIR)as [1],
> > rather than $(COMPAT_GCC_TOOLCHAIN_DIR)$(CROSS_COMPILE_COMPAT)as,
> > resulting in the following build error:
> >
> > $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- \
> > CROSS_COMPILE_COMPAT=arm-linux-gnueabi- LLVM=1 O=out/aarch64 distclean \
> > defconfig arch/arm64/kernel/vdso32/
> > ...
> > /home/nathan/cbl/toolchains/llvm-binutils/bin/as: unrecognized option '-EL'
> > clang-12: error: assembler command failed with exit code 1 (use -v to see invocation)
> > make[3]: *** [arch/arm64/kernel/vdso32/Makefile:181: arch/arm64/kernel/vdso32/note.o] Error 1
> > ...
> >
> > Adding the value of CROSS_COMPILE_COMPAT (adding notdir to account for a
> > full path for CROSS_COMPILE_COMPAT) fixes this issue, which matches the
> > solution done for the main Makefile [2].
> >
> 
> [ CC Masahiro ]
> 
> Masahiro added a slightly adapted version of [2] in <kbuild.git#fixes>.
> Shall this go through kbuild subsystem or folded into [1]?
> 
> - Sedat -
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git/commit/?h=fixes&id=ca9b31f6bb9c6aa9b4e5f0792f39a97bbffb8c51

Sorry, should have cc'd Masahiro, slipped my mind.

Note, I kept this separate as the patches have to go back different
distances; only 5.7 has working clang support for vdso32, see
commit a5d442f50a41 ("arm64: vdso32: Enable Clang Compilation") in
Linus' tree, which appeared in 5.7-rc1 so this only needs to go into
linux-5.7.y. The main patch needs to back all the way to 4.4 so we would
need to drop this hunk when backporting, which would be annoying, as the
main patch backports cleanly to 4.9.

It could be routed via the kbuild tree but the arm64 maintainers are
pretty good at getting these fixes into the hands of Linus so I see no
reason to go around them.

Cheers,
Nathan

> > [1]: https://github.com/llvm/llvm-project/commit/3452a0d8c17f7166f479706b293caf6ac76ffd90
> > [2]: https://lore.kernel.org/lkml/20200721173125.1273884-1-maskray@google.com/
> >
> > Cc: stable@...r.kernel.org
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1099
> > Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> > ---
> >  arch/arm64/kernel/vdso32/Makefile | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> > index d88148bef6b0..5139a5f19256 100644
> > --- a/arch/arm64/kernel/vdso32/Makefile
> > +++ b/arch/arm64/kernel/vdso32/Makefile
> > @@ -14,7 +14,7 @@ COMPAT_GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE_COMPAT)elfedit))
> >  COMPAT_GCC_TOOLCHAIN := $(realpath $(COMPAT_GCC_TOOLCHAIN_DIR)/..)
> >
> >  CC_COMPAT_CLANG_FLAGS := --target=$(notdir $(CROSS_COMPILE_COMPAT:%-=%))
> > -CC_COMPAT_CLANG_FLAGS += --prefix=$(COMPAT_GCC_TOOLCHAIN_DIR)
> > +CC_COMPAT_CLANG_FLAGS += --prefix=$(COMPAT_GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE_COMPAT))
> >  CC_COMPAT_CLANG_FLAGS += -no-integrated-as -Qunused-arguments
> >  ifneq ($(COMPAT_GCC_TOOLCHAIN),)
> >  CC_COMPAT_CLANG_FLAGS += --gcc-toolchain=$(COMPAT_GCC_TOOLCHAIN)
> >
> > base-commit: d15be546031cf65a0fc34879beca02fd90fe7ac7
> > --
> > 2.28.0.rc1
> >
> > --
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