Re: [PATCH v7.1 07/13] ARC: Linux Syscall Interface

[Joseph Myers <joseph@codesourcery.com>]

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
joseph@codesourcery.com

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