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Re: gdbstub initial code, v7
- From: Roland McGrath <roland at redhat dot com>
- To: Oleg Nesterov <oleg at redhat dot com>
- Cc: utrace-devel at redhat dot com, archer at sourceware dot org
- Date: Wed, 13 Oct 2010 00:23:46 -0700 (PDT)
- Subject: Re: gdbstub initial code, v7
- References: <20100830185850.GA1132@redhat.com><20100830192040.GA15431@host1.dyn.jankratochvil.net><20100831072048.GA26362@host1.dyn.jankratochvil.net><20100902200632.GA23692@redhat.com><20100903064008.GA16249@host1.dyn.jankratochvil.net><20100903230957.GC8917@redhat.com><20100910101452.39015405D5@magilla.sf.frob.com><20100910182903.GB27699@redhat.com><20100910190547.85CBD405D5@magilla.sf.frob.com><20100910192001.GA30490@redhat.com>
> On 09/10, Roland McGrath wrote:
> > > ugdb sets "please stop" flag and does utrace_control(INTERRUPT). However,
> > > in unlikely case the tracee can stop before ->report_signal() reporting
> > I don't think this is the right thing to do. When the intent is explicitly
> > to interrupt, there is no reason to stop before the interruption is
> > complete, i.e. report_signal.
> This means that ugdb_report_quiesce() should never return UTRACE_STOP,
> and that is all.
I'm not sure about this.
> But what about multitracing? Suppose that "(gdb) interrupt" happens
> just before, say, do_report_syscall_entry() and another engine wants
> to stop. If ugdb_report_quiesce() doesn't return UTRACE_STOP, then
> gdb will wait until another debugger resumes the tracee.
Yes, I do think that's a problem. We want gdb to report back promptly.
One possibility is to have report_quiesce notice its argument is
UTRACE_EVENT(SYSCALL_ENTRY) and roll back to before the syscall.
That is, it enables SYSCALL_ENTRY and SYSCALL_EXIT reporting, then
its report_syscall_entry uses UTRACE_SIGNAL_ABORT, report_syscall_exit
does syscall_set_return_value(-ERESTARTNOHAND, 0) and then returns
UTRACE_INTERRUPT. Now, we'll reenter a UTRACE_SIGNAL_REPORT callback
"before" the system call, and we can stop there without being in any