Fix Arm __ASSUME_COPY_FILE_RANGE (bug 23915) [committed]

[Florian Weimer]

* Joseph Myers:

> On Mon, 26 Nov 2018, Florian Weimer wrote:
>
>> * Joseph Myers:
>> 
>> > 2018-11-23  Joseph Myers  <joseph@codesourcery.com>
>> >
>> > 	[BZ #23915]
>> > 	* sysdeps/unix/sysv/linux/arm/kernel-features.h
>> > 	[__LINUX_KERNEL_VERSION < 0x040700] (__ASSUME_COPY_FILE_RANGE):
>> > 	Undefine.
>> 
>> So I feel kind of bad about this—I looked for such issues after the
>> first problems cropped up and just didn't seem them in the kernel source
>> tree.
>> 
>> Assuming that I'm going to implement a few system call wrappers in the
>> future, how can I do a better job here?
>
> My approach is to examine the diffs for the kernel version that introduced 
> the syscall, and check whether it's present (asm/unistd.h, and syscall 
> table, and any relevant compat syscall table) for each (architecture, ABI) 
> pair supported by glibc not using the asm-generic syscall ABI.

Can we put a list somewhere of the files that need checking, for the
supported glibc architectures?

> What we really need is for the kernel to do a better job at introducing 
> syscalls at the same time on all architectures, rather than just adding 
> them for one or two architectures, leaving it to architecture maintainers 
> to fill in the rest and so resulting in long delays before glibc can 
> actually assume a syscall to be available everywhere.

Agreed.

Thanks,
Florian