On Mon, Oct 24, 2011 at 04:41:27PM +0200, Oleg Nesterov wrote: > On 10/22, Ananth N Mavinakayanahalli wrote: > > > > On Wed, Oct 19, 2011 at 11:53:44PM +0200, Oleg Nesterov wrote: > > > Finally, add UTASK_SSTEP_TRAPPED state/code to handle the case when > > > xol insn itself triggers the signal. > > > > > > In this case we should restart the original insn even if the task is > > > already SIGKILL'ed (say, the coredump should report the correct ip). > > > This is even more important if the task has a handler for SIGSEGV/etc, > > > The _same_ instruction should be repeated again after return from the > > > signal handler, and SSTEP can never finish in this case. > > > > Oleg, > > > > Not sure I understand this completely... > > I hope you do not think I do ;) I think you understand it better than you think you do :-) > > When you say 'correct ip' you mean the original vaddr where we now have > > a uprobe breakpoint and not the xol copy, right? > > Yes, > > > Coredump needs to report the correct ip, but should it also not report > > correctly the instruction that caused the signal? Ergo, shouldn't we > > put the original instruction back at the uprobed vaddr? > > OK, now I see what you mean. I was confused by the "restore the original > instruction before _restart_" suggestion. > > Agreed! it would be nice to "hide" these int3's if we dump the core, but > I think this is a bit off-topic. It makes sense to do this in any case, > even if the core-dumping was triggered by another thread/insn. It makes > sense to remove all int3's, not only at regs->ip location. But how can > we do this? This is nontrivial. I don't think that is a problem.. see below... > And. Even worse. Suppose that you do "gdb probed_application". Now you > see int3's in the disassemble output. What can we do? In this case, nothing. > I think we can do nothing, at least currently. This just reflects the > fact that uprobe connects to inode, not to process/mm/etc. > > What do you think? Thinking further on this, in the normal 'running gdb on a core' case, we won't have this problem, as the binary that we point gdb to, will be a pristine one, without the uprobe int3s, right? Ananth -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>