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Date:   Thu, 27 Jul 2023 14:36:48 -0700
From:   Nathan Chancellor <nathan@kernel.org>
To:     Tiezhu Yang <yangtiezhu@loongson.cn>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        linux-arm-kernel@lists.infradead.org,
        linux-riscv@lists.infradead.org, loongarch@lists.linux.dev,
        linux-arch@vger.kernel.org, bpf@vger.kernel.org,
        linux-perf-users@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org, loongson-kernel@lists.loongnix.cn
Subject: Re: [PATCH v3 1/2] asm-generic: Unify uapi bitsperlong.h for arm64,
 riscv and loongarch
Message-ID: <20230727213648.GA354736@dev-arch.thelio-3990X>
References: <1687443219-11946-1-git-send-email-yangtiezhu@loongson.cn>
 <1687443219-11946-2-git-send-email-yangtiezhu@loongson.cn>
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Hi Tiezhu and Arnd,

On Thu, Jun 22, 2023 at 10:13:38PM +0800, Tiezhu Yang wrote:
> Now we specify the minimal version of GCC as 5.1 and Clang/LLVM as 11.0.0
> in Documentation/process/changes.rst, __CHAR_BIT__ and __SIZEOF_LONG__ are
> usable, it is probably fine to unify the definition of __BITS_PER_LONG as
> (__CHAR_BIT__ * __SIZEOF_LONG__) in asm-generic uapi bitsperlong.h.
> 
> In order to keep safe and avoid regression, only unify uapi bitsperlong.h
> for some archs such as arm64, riscv and loongarch which are using newer
> toolchains that have the definitions of __CHAR_BIT__ and __SIZEOF_LONG__.
> 
> Suggested-by: Xi Ruoyao <xry111@xry111.site>
> Link: https://lore.kernel.org/all/d3e255e4746de44c9903c4433616d44ffcf18d1b.camel@xry111.site/
> Suggested-by: Arnd Bergmann <arnd@arndb.de>
> Link: https://lore.kernel.org/linux-arch/a3a4f48a-07d4-4ed9-bc53-5d383428bdd2@app.fastmail.com/
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
>  arch/arm64/include/uapi/asm/bitsperlong.h          | 24 ----------------------
>  arch/loongarch/include/uapi/asm/bitsperlong.h      |  9 --------
>  arch/riscv/include/uapi/asm/bitsperlong.h          | 14 -------------
>  include/uapi/asm-generic/bitsperlong.h             | 13 +++++++++++-
>  tools/arch/arm64/include/uapi/asm/bitsperlong.h    | 24 ----------------------
>  .../arch/loongarch/include/uapi/asm/bitsperlong.h  |  9 --------
>  tools/arch/riscv/include/uapi/asm/bitsperlong.h    | 14 -------------
>  tools/include/uapi/asm-generic/bitsperlong.h       | 14 ++++++++++++-
>  tools/include/uapi/asm/bitsperlong.h               |  6 ------
>  9 files changed, 25 insertions(+), 102 deletions(-)
>  delete mode 100644 arch/arm64/include/uapi/asm/bitsperlong.h
>  delete mode 100644 arch/loongarch/include/uapi/asm/bitsperlong.h
>  delete mode 100644 arch/riscv/include/uapi/asm/bitsperlong.h
>  delete mode 100644 tools/arch/arm64/include/uapi/asm/bitsperlong.h
>  delete mode 100644 tools/arch/loongarch/include/uapi/asm/bitsperlong.h
>  delete mode 100644 tools/arch/riscv/include/uapi/asm/bitsperlong.h

I think this change has backwards compatibility concerns, as it breaks
building certain host tools on the stable releases (at least 6.4 and
6.1, as that is where I noticed this). I see the following error on my
aarch64 system:

  $ make -skj"$(nproc)" ARCH=x86_64 CROSS_COMPILE=x86_64-linux- mrproper defconfig prepare
  In file included from /usr/include/asm/bitsperlong.h:1,
                   from /usr/include/asm-generic/int-ll64.h:12,
                   from /usr/include/asm-generic/types.h:7,
                   from /usr/include/asm/types.h:1,
                   from tools/include/linux/types.h:13,
                   from tools/arch/x86/include/asm/orc_types.h:9,
                   from scripts/sorttable.h:96,
                   from scripts/sorttable.c:201:
  tools/include/asm-generic/bitsperlong.h:14:2: error: #error Inconsistent word size. Check asm/bitsperlong.h
     14 | #error Inconsistent word size. Check asm/bitsperlong.h
        |  ^~~~~

A reverse bisect of 6.4 to 6.5-rc1 points to this patch. This Fedora
rawhide container has kernel-headers 6.5.0-0.rc2.git0.1.fc39 and the
error disappears when I downgrade to 6.4.0-0.rc7.git0.1.fc39. I have not
done a ton of triage/debugging so far, as I am currently hunting down
other regressions, but I figured I would get an initial report out,
since I noticed it when validating LLVM from the new release/17.x
branch. If there is any additional information I can provide or patches
I can test, I am more than happy to do so.

Cheers,
Nathan