[PATCH v2] AArch64: Check kernel version for SVE ifuncs

[Florian Weimer]

* Szabolcs Nagy:

> The 03/18/2024 14:14, Wilco Dijkstra wrote:
>> 
>> v2: Add __LINUX_KERNEL_VERSION #ifdefs, improve parser, use 8:8:8 format.
>> 
>> Old Linux kernels disable SVE after every system call.  Calling the
>> SVE-optimized memcpy afterwards will then cause a trap to reenable SVE.
>> As a result, applications with a high use of syscalls may run slower with
>> the SVE memcpy.  This is true for kernels between 4.15.0 and before 6.2.0,
>> except for 5.14.0 which was patched.  Avoid this by checking the kernel
>> version and selecting the SVE ifunc on modern kernels.
>> 
>> Parse the kernel version reported by uname() into a 24-bit kernel.major.minor
>> value without calling any library functions.  If uname() is not supported or
>> if the version format is not recognized, assume the kernel is modern.
>> 
>> Passes regress, OK for commit?
>
> OK to commit. (clearly a hack but what can we do..)
>
> Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>

I have not had a chance to test this yet with the el9 kernel.

I will try to do this tomorrow.

Do we need to include other distribution LTS kernels in the version
check?

Thanks,
Florian