linux-kernel - Re: [RFC PATCH] asm-generic: Unify uapi bitsperlong.h

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Date:   Thu, 08 Jun 2023 14:56:30 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Tiezhu Yang" <yangtiezhu@...ngson.cn>
Cc:     Linux-Arch <linux-arch@...r.kernel.org>,
        linux-s390@...r.kernel.org, llvm@...ts.linux.dev,
        linux-ia64@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-parisc@...r.kernel.org, x86@...nel.org,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, loongarch@...ts.linux.dev,
        linux-alpha@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
        bpf@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        loongson-kernel@...ts.loongnix.cn
Subject: Re: [RFC PATCH] asm-generic: Unify uapi bitsperlong.h

On Thu, Jun 8, 2023, at 09:04, Tiezhu Yang wrote:
> On 05/09/2023 05:37 PM, Arnd Bergmann wrote:
>> On Tue, May 9, 2023, at 09:05, Tiezhu Yang wrote:
>>
>> I think we are completely safe on the architectures that were
>> added since the linux-3.x days (arm64, riscv, csky, openrisc,
>> loongarch, nios2, and hexagon), but for the older ones there
>> is a regression risk. Especially on targets that are not that
>> actively maintained (sparc, alpha, ia64, sh, ...) there is
>> a good chance that users are stuck on ancient toolchains.
>> It's probably also a safe assumption that anyone with an older
>> libc version won't be using the latest kernel headers, so
>> I think we can still do this across architectures if both
>> glibc and musl already require a compiler that is new enough,
>> or alternatively if we know that the kernel headers require
>> a new compiler for other reasons and nobody has complained.
>>
>> For glibc, it looks the minimum compiler version was raised
>> from gcc-5 to gcc-8 four years ago, so we should be fine.
>>
>> In musl, the documentation states that at least gcc-3.4 or
>> clang-3.2 are required, which probably predate the
>> __SIZEOF_LONG__ macro. On the other hand, musl was only
>> released in 2011, and building musl itself explicitly
>> does not require kernel uapi headers, so this may not
>> be too critical.
>>
>> There is also uClibc, but I could not find any minimum
>> supported compiler version for that. Most commonly, this
>> one is used for cross-build environments, so it's also
>> less likely to have libc/gcc/headers being wildly out of
>> sync. Not sure.
>>
>>       Arnd
>>
>> [1] https://sourceware.org/pipermail/libc-alpha/2019-January/101010.html
>>
>
> Thanks Arnd for the detailed reply.
> Any more comments? What should I do in the next step?

I think the summary is "it's probably fine", but I don't know
for sure, and it may not be worth the benefit.

Maybe you can prepare a v2 that only does this for the newer
architectures I mentioned above, with and an explanation and
link to my above reply in the file comments?

      Arnd