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

Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> · Fri, 9 Jun 2023 14:50:58 +0800

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