> UPROBE_COPY_INSN, UPROBE_SKIP_SSTEP, and uprobe->flags must die. This > patch kills UPROBE_SKIP_SSTEP. I never understood why it was added; > not only it doesn't help, it harms. > > It can only help to avoid arch_uprobe_skip_sstep() if it was already > called before and failed. But this is ugly, if we want to know whether > we can emulate this instruction or not we should do this analysis in > arch_uprobe_analyze_insn(), not when we hit this probe for the first > time. > > And in fact this logic is simply wrong. arch_uprobe_skip_sstep() can > fail or not depending on the task/register state, if this insn can be > emulated but, say, put_user() fails we need to xol it this time, but > this doesn't mean we shouldn't try to emulate it when this or another > thread hist this bp next time. > > And this is the actual reason for this change. We need to emulate the > "call" insn, but push(return-address) can obviously fail. > > Per-arch notes: > > x86: __skip_sstep() can only emulate "rep;nop". With this > change it will be called every time and most probably > for no reason. > > This will be fixed by the next changes. We need to > change this suboptimal code anyway. > > arm: Should not be affected. It has its own "bool simulate" > flag checked in arch_uprobe_skip_sstep(). > > ppc: Looks like, it can emulate almost everything. Does it > actually needs to record the fact that emulate_step() > failed? Hopefully not. But if yes, it can add the ppc- > specific flag into arch_uprobe. > > TODO: rename arch_uprobe_skip_sstep() to arch_uprobe_emulate_insn(), > > Signed-off-by: Oleg Nesterov <o...@redhat.com>
Acked-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com> -- Thanks and Regards Srikar Dronamraju -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
