On Tue, 7 Jul 2020, Vineet Gupta via Libc-alpha wrote:
> > Each implementation has it ows requirements so I can't really say if
> > a helper function does make sense for all of them. For pause
> > specifically we can even simplify to since all architectures have
> > either ppoll or ppoll_time64:
> >
> > int
> > __libc_pause (void)
> > {
> > #ifdef __NR_ppoll_time64
> > return SYSCALL_CANCEL (ppoll_time64, NULL, 0, NULL, NULL);
> > #else
> > return SYSCALL_CANCEL (ppoll, NULL, 0, NULL, NULL);
> > #endif
> > }
>
> But how is this compatible with older kernels (and perhaps this is a general
> question). I mean one/more ABIs minimum kernel would not have the ppoll or
> ppoll64
> so how will new glibc work with such a kernel ? Is it not required to ?
See commit 089b772f98afd9eb6264c6489bc96a30bf6af4ac, where I removed
__ASSUME_PPOLL because all supported kernel versions now had that syscall
for all glibc architectures.
In general this sort of thing needs a review of whether a given syscall is
available for all glibc architectures in their minimum kernel versions.
For the old kernels in question, that means checking the
architecture-specific syscall table as used to dispatch syscalls at
runtime, which used to have an architecture-specific format before
unification work was done; it used to mean checking asm/unistd.h as well,
but now we have syscall tables in glibc that's probably no longer
required. It also involves checking compat syscall tables for 32-bit
binaries on 64-bit kernels, as sometimes a syscall didn't get added to the
native and compat syscall tables at the same time (see the comments in
sparc/kernel-features.h about various socket-related syscalls, for
example).
--
Joseph S. Myers
jos...@codesourcery.com
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