new syscall stub support for ia64 libc

[Roland McGrath]

> Can you readelf -Wl arch/ia64/kernel/gate.so |grep LOAD (or grep -A1 LOAD
> instead), or better yet readelf -Wa arch/ia64/kernel/gate.so ? I'd like
> to understand why you need the second LOAD segment, what stuff has it in
> etc.

There are two LOAD segments for the same one page of file data mapped into
two consecutive pages with different permissions.  The first segment is
read-only and the second is execute-only.  The execute-only permission
(cannot be read by user mode) is required for the magic EPC instruction.
Hence we need two mappings to see the DSO info and to execute.

> IMHO NEED_DL_SYSINFO should be defined in both NPTL and
> Linuxthread ia64/dl-sysdep.h, while USE_DL_SYSINFO only in NPTL.
> And sysdep.h should use sysinfo only if USE_DL_SYSINFO is defined.
> Then linuxthreads will work just fine (use break always, who cares)
> and NPTL will use VDSO.

Agreed.  THis is what i386 does.