[PATCH] PowerPC: bp-permanent.exp, kill-after-signal fix

[Ulrich Weigand]

will schmidt <will_schmidt@vnet.ibm.com> wrote:

>So..  Is this directly related to the amount of kernel code handling
>the signals?  i.e. Would this need to be updated if another
instruction
>is added to the kernel code?

To clarify, this not *kernel* code, it's user space code, but code
that is placed by the kernel into user space (in the vdso).

Many platforms today use the vdso in the signal *return* path, but
Power seems special in that it is using a vdso instruction also to
*enter* a signal handler in the first place.  (So instead of the
kernel directly dispatching to the installed signal handler, it
first dispatches to vdso code which in turn calls into the signal
handler.)

Reading the kernel logs, this seems to have been a performance
optimization to prevent the call/return stack from getting out
of balance.

That vdso code path when entering a signal handler is just a
single "brctl"; I don't see any particular reason why this would
ever need to become any longer.

Bye,
Ulrich