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Re: [PATCH] powerpc: Enable demuxed sysv IPC syscalls

On Thu, 3 Dec 2015, Adhemerval Zanella wrote:

> On 03-12-2015 20:22, Joseph Myers wrote:
> > On Thu, 3 Dec 2015, Adhemerval Zanella wrote:
> > 
> >> My inclination would to avoid the __ASSUME_XXX macros definition and just
> >> check if the current kernel header defines of not __NR_msgctl and use it
> >> as the condition to enable the wire-up syscall.
> > 
> > I'm not clear exactly what you're suggesting.  If you check like that 
> > (whether the kernel headers, possibly for a newer kernel than the minimum 
> > supported by that glibc build, define a syscall number) then you need a 
> > run-time fallback if the new syscall fails with ENOSYS.
> But building with a newer kernel header will bind the to the
> specific version, isn't? I am assuming ENOSYS will be retuned only when

No.  You should almost always build with the newest kernel headers 
available so that glibc contains the support for new syscalls etc. (which 
may or may not work at runtime depending on the kernel headers version 
used then).  Each of (kernel headers version, kernel version used at 
runtime) must be at least (minimum kernel version specified with 
--enable-kernel), but there is no ordering requirement between (kernel 
headers version) and (kernel version used at runtime).  Use of new 
syscalls to implement functionality previously supported on older kernels 
needs runtime fallback unless restricted with --enable-kernel (for 
completely new functionality, we can judge case-by-case how useful 
fallbacks are).

Joseph S. Myers

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