Re: [PATCH] linux: Allow avoiding va_list for generic syscall and use it for LoongArch

[Florian Weimer <fw@deneb.enyo.de>]

* Xi Ruoyao:

> On Fri, 2023-03-24 at 10:47 +0100, Florian Weimer wrote:
>> * Xi Ruoyao via Libc-alpha:
>> 
>> > Currently GCC generates highly sub-optimal code on architectures
>> > where
>> > the calling convention prefers registers for arugment passing.  This
>> > is
>> 
>> Typo: ar[gu]ment
>> 
>> > LoongArch is benefited from this (saving about 430 CPU cycles per
>> > syscall, though I won't call it a significant improvement because
>> > syscall is "slow" in nature).  And in the future we may switch more
>> > ports to use the generic syscall without a performance regression,
>> > reducing the number of target-specific syscall.{c,S} files we need
>> > to
>> > maintain.
>> 
>> Does this impact the open* and fcntl* wrappers as well?
>
> Yes, on LoongArch all GARs are saved :(.  I'll see if it's possible to
> avoid using va_list for them too.

If we had overread the argument list in open*, that certainly would
have avoided all the grief we had with O_TMPFILE (where the original
glibc implementation did not pass the mode argument to the kernel).  I
think fcntl* already overreads the argument list, so it should be
safe.