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

[Tiezhu Yang]

On 06/08/2023 08:56 PM, Arnd Bergmann wrote:
> 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.

Thank you, it is very clear now.

> 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?

Only arm64, riscv and loongarch belong to the newer architectures
which are related with this change, I am not sure it is necessary
to "unify" uapi bitsperlong.h for them.

Anyway, let me try, I will send a new version, maybe this is going
to progress in the right direction.

Thanks,
Tiezhu