On 01/05, Martin Schwidefsky wrote: > > On Tue, 5 Jan 2010 16:36:33 +0100 > Oleg Nesterov <o...@redhat.com> wrote: > > > For example, why do_signal() sets TIF_SINGLE_STEP? Why can't we do > > > > --- a/arch/s390/kernel/signal.c > > +++ b/arch/s390/kernel/signal.c > > @@ -500,18 +500,10 @@ void do_signal(struct pt_regs *regs) > > clear_thread_flag(TIF_RESTORE_SIGMASK); > > > > /* > > - * If we would have taken a single-step trap > > - * for a normal instruction, act like we took > > - * one for the handler setup. > > - */ > > - if (current->thread.per_info.single_step) > > - set_thread_flag(TIF_SINGLE_STEP); > > - > > - /* > > * Let tracing know that we've done the handler > > setup. > > */ > > tracehook_signal_handler(signr, &info, &ka, > > regs, > > - > > test_thread_flag(TIF_SINGLE_STEP)); > > + > > current->thread.per_info.single_step); > > } > > return; > > } > > > > ? > > The reason why we set the TIF_SINGLE_STEP bit in do_signal is that we > want to be able to stop the debugged program before the first > instruction of the signal handler has been executed. The PER single > step causes a trap after an instruction has been executed. That first > instruction can do bad things to the arguments of the signal handler..
Yes, but afaics all we need is to pass the correct "int stepping" arg to tracehook_signal_handler(). If it is true, the tracee does ptrace_notify() before it returns to user-mode. > > dmesg shows 799 lines of > > > > XXX: 2389 0 > > > > > > The kernel is 2.6.32.2 + utrace, but CONFIG_UTRACE is not set. > > With or without my bug fix ? With, but please see another email. I'll add clear_bit(TIF_SINGLE_STEP) into do_fork() path and re-test. Oleg.
