Messages in this thread | | | Date | Thu, 28 Apr 2005 15:41:39 +0200 | From | Bodo Stroesser <> | Subject | Re: Again: UML on s390 (31Bit) |
| |
Martin Schwidefsky wrote: > So (!entryexit & regs->gprs[2] < 0) translates to the debugger changed the > guest > system call to something illegal on the first of the two ptrace calls. So > the > patch doesn't hurt for normal, non-ptraced operation but it might hurt > other > users of ptrace. I don't think, it hurts. If a debugger willingly sets the syscall number to -1, what would happen without the patch? The kernel will set the result -ENOSYS into grps[2]. So, even if trap still indicates a syscall and a signal is pending, no syscall restarting will be done. With the patch, a debugger would observe changed behavior of the kernel *only*, if it writes the syscall number to -1 on the first syscall interception and then writes the result to ERESTARTXXXXX on the second, while at the same time a signal is pending for the debugged process.
I assumed, that non of the current users of ptrace exactly does this. If I'm wrong here, the patch *really* is bad.
> Ok, I think I've understood the problem now. What you are basically have is > a process running in a UML guest that happens to have -ERESTARTXXX in grp2 > when it gets interrupted. A signal is delivered and on return from that > signal > with sys_(rt_)sigreturn >another< signal might be pending and then > do_signal > gets confused because of -ERESTARTXXX in grp2. This other signal must be pending on the *host*, in UML, this might be SIGVTALRM.
> For normal, non-uml operation > restore_sigregs resets regs->trap to -1 which avoids the confusion. With > UML > the host intercepts sys_rt_sigreturn and does whatever needs to be done for > the guest >except< resetting regs->trap to -1. So the problem seems to be > that you need a ptrace interface to do that. I don't think it is a good > idea > to kludge syscall_trace to reset regs->trap under some conditions. My idea was to enable the existing ptrace interface to do what UML needs, without changing it in a way observable to other users of ptrace. I expected my patch to exactly do that, but maybe I missed something. Any better idea is welcome.
Regards, Bodo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |