linux-kernel - Re: [PATCH v2 0/2] sparc/build: Rework CFLAGS for clang compatibility

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Message-ID: <CAK7LNASTkUTK8JZCzySNh3BVKxauusVKRhjnchy6iZz4qLbq8w@mail.gmail.com>
Date: Wed, 23 Oct 2024 04:10:01 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Koakuma <koachan@...tonmail.com>, Andreas Larsson <andreas@...sler.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, "David S. Miller" <davem@...emloft.net>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, glaubitz@...sik.fu-berlin.de, 
	Nicolas Schier <nicolas@...sle.eu>, sparclinux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, 
	linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v2 0/2] sparc/build: Rework CFLAGS for clang compatibility

On Tue, Oct 22, 2024 at 5:17 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Hi Andreas,
>
> On Wed, Jul 17, 2024 at 11:10:14PM +0700, Koakuma wrote:
> > This changes the CFLAGS for building the SPARC kernel so that it can be
> > built with clang, as a follow up from the discussion in this thread:
> >
> > https://lore.kernel.org/lkml/JAYB7uS-EdLABTR4iWZdtFOVa5MvlKosIrD_cKTzgeozCOGRM7lhxeLigFB1g3exX445I_W5VKB-tAzl2_G1zCVJRQjp67ODfsSqiZWOZ9o=@protonmail.com/T/#u
> ...
> > Building with these changes still result in a working kernel,
> > at least for Sun T5120, Oracle T4-1, and qemu virtual machines.
> >
> > On the LLVM side, the effort for building Linux/SPARC is tracked here:
> > https://github.com/llvm/llvm-project/issues/40792
> >
> > Signed-off-by: Koakuma <koachan@...tonmail.com>
> > ---
> > Changes in v2:
> > - Remove the -mv8plus change; it will be handled on clang side:
> >   https://github.com/llvm/llvm-project/pull/98713
> > - Add CLANG_TARGET_FLAGS as suggested in v1 review.
> > - Link to v1: https://lore.kernel.org/r/20240620-sparc-cflags-v1-1-bba7d0ff7d42@protonmail.com
> >
> > ---
> > Koakuma (2):
> >       sparc/build: Remove all usage of -fcall-used* flags
> >       sparc/build: Add SPARC target flags for compiling with clang
> >
> >  arch/sparc/Makefile      | 4 ++--
> >  arch/sparc/vdso/Makefile | 2 +-
> >  scripts/Makefile.clang   | 1 +
> >  3 files changed, 4 insertions(+), 3 deletions(-)
>
> Would you be able to help move this series [1] and its companion patch
> for the vDSO [2] along to Linus for 6.13? If you are not able to for
> whatever reason but the changes look reasonable to you, would you be
> able to provide an Ack so it can be chauffeured by someone else, such as
> Masahiro/Kbuild or Andrew/-mm?
>
> For the record, I retested these three changes on top of 6.12-rc4, where
> they still apply cleanly. Now that the LLVM PR linked above (98713) has
> been merged into LLVM main, a clang built straight from llvm-project.git
> can build the kernel with this series (I tested at dca43a1c82f1).
>
> [1]: https://lore.kernel.org/all/20240717-sparc-cflags-v2-0-259407e6eb5f@protonmail.com/
> [2]: https://lore.kernel.org/all/20240808-sparc-shr64-v2-1-fd18f1b2cea9@protonmail.com/
>
> Cheers,
> Nathan



I applied this patch set, but I still observe a build error.


masahiro@zoe:~/workspace/linux-kbuild(kbuild)$
~/tools/llvm-latest/bin/clang --version
ClangBuiltLinux clang version 20.0.0git
(https://github.com/llvm/llvm-project.git
d1401822e2d2753bed3ac597a42cc0b261de40a4)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /home/masahiro/tools/llvm-latest/bin
masahiro@zoe:~/workspace/linux-kbuild(kbuild)$ make
LLVM=~/tools/llvm-latest/bin/  ARCH=sparc sparc64_defconfig all
  HOSTCC  scripts/basic/fixdep
  HOSTCC  scripts/kconfig/conf.o
  HOSTCC  scripts/kconfig/confdata.o
  HOSTCC  scripts/kconfig/expr.o
  HOSTCC  scripts/kconfig/lexer.lex.o
  HOSTCC  scripts/kconfig/menu.o
  HOSTCC  scripts/kconfig/parser.tab.o
  HOSTCC  scripts/kconfig/preprocess.o
  HOSTCC  scripts/kconfig/symbol.o
  HOSTCC  scripts/kconfig/util.o
  HOSTLD  scripts/kconfig/conf
#
# configuration written to .config
#
  SYNC    include/config/auto.conf.cmd
  HOSTCC  scripts/genksyms/genksyms.o
  HOSTCC  scripts/genksyms/parse.tab.o
  HOSTCC  scripts/genksyms/lex.lex.o
  HOSTLD  scripts/genksyms/genksyms
  HOSTCC  scripts/kallsyms
  UPD     include/generated/compile.h
  CC      scripts/mod/empty.o
clang: error: unsupported argument '--undeclared-regs' to option '-Wa,'
make[3]: *** [scripts/Makefile.build:229: scripts/mod/empty.o] Error 1
make[2]: *** [Makefile:1208: prepare0] Error 2
make[1]: *** [/home/masahiro/workspace/linux-kbuild/Makefile:347:
__build_one_by_one] Error 2
make: *** [Makefile:224: __sub-make] Error 2



-- 
Best Regards
Masahiro Yamada