ppc64 vDSO update

[Benjamin Herrenschmidt]

At the URL below, you can find a new version of the ppc64 vDSO patch against
a recent Linus bk tree. I intend to submit it upstream real soon as the work
on non-executable stack is waiting for it, though we must first make sure the
way symbols are exported to userland is ok for glibc.

http://gate.crashing.org/~benh/ppc64-vdso-20041122.diff

Following various comments, I've changed the way the 64 bits vDSO exports symbols,
it now no-longer has function descriptors & "dot" symbols, the symbols point
directly to the functions with a link base of 0 (so the symbol value is really an
offset to the code now). You can still build the old way though with a #define in
include/asm-ppc64/vdso.h, at least until we have formally agreed on what mecanism
we want to use.

(Craig: the signal issue is fixed now, either when building with descriptors or
without).

Ben.