[PATCH 1/2] powerpc/jprobes: Save and restore the parameter save area

[Michael Ellerman]

"Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com> writes:

> As pointed out in x86 setjmp_pre_handler(), we need to save and restore
> the parameter save area since the jprobe hook might overwrite it. Since
> there is no easy way to identify the size of the parameter save area,
> we choose to save/restore a fixed 16 [double]word-sized area including
> the stack frame header.
>
> We introduce STACK_FRAME_PARM_SAVE to encode the offset of the parameter
> save area from the stack frame pointer. Remove the similarly named
> PARAMETER_SAVE_AREA_OFFSET in ptrace.c as those are currently not used
> anywhere.
>
> Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
> ---
> Michael,
> I've set the limit to 16 parameters as being a "reasonable" number, but
> we could very well make this 24 or 32 if we want to be sure. Let me
> know what you prefer.

That sounds incredibly fragile. Are we really just guessing at the size
required? What happens if we under estimate, do we crash, silently
corrupt data .. ?

cheers