[lldb-dev] SBProcess::Detach kills target

Thu Mar 31 14:44:20 PDT 2016

OK, I got the picture, thanks a lot!
     > What is it that you are trying to do anyway?

Well, target termination during detach is unexpected, so my customers might get confused. Fortunately I am in control of the target program too, so I'll just ignore SIGHUP for the time being.
Thanks,Eugene

> From: labath at google.com
> Date: Thu, 31 Mar 2016 09:16:06 +0100
> Subject: Re: [lldb-dev] SBProcess::Detach kills target
> To: eugenebi at hotmail.com
> CC: lldb-dev at lists.llvm.org
> 
> We are not sending the SIGHUP, it is automatically getting sent by the
> OS when the master end of the pty gets closed. The reason you are not
> seeing this in the attach scenario is that we do not intercept
> inferior stdio in this case (it's not possible, or desirable, since
> the process is already running). This is also the reason
> SBProcess.GetSTDOUT does not return anything in the attach scenario. I
> am not familiar with the details of the Mac implementation and I
> cannot tell you why is this not happening there.
> I guess one way to fix this would be to have a special mode of
> starting the inferior without a controlling terminal, but I am not
> sure if this would be a generally useful feature. What is it that you
> are trying to do anyway?
> 
> pl
> 
> On 30 March 2016 at 23:03, Eugene Birukov <eugenebi at hotmail.com> wrote:
> > Just a wild guess - is this SIGHUP because stdin/stdout are broken? I.e. the
> > debugger closes its pty's on detach and that causes the signal?
> > What is the behavior on MAC?
> >
> > ________________________________
> > To: labath at google.com
> > Date: Wed, 30 Mar 2016 14:49:33 -0700
> > CC: lldb-dev at lists.llvm.org
> > Subject: Re: [lldb-dev] SBProcess::Detach kills target
> > From: lldb-dev at lists.llvm.org
> >
> >
> > Right, my bad. The problem was that when debugger detaches the stdio does
> > not go anywhere so I failed to see my printf.
> >
> > Still, is this how it is supposed to be? I naively assume that if we don't
> > send SIGHUP in attach scenario we should not send it in launch scenario too.
> >
> > Thanks,
> > Eugene
> >
> >> From: labath at google.com
> >> Date: Wed, 30 Mar 2016 10:22:33 +0100
> >> Subject: Re: [lldb-dev] SBProcess::Detach kills target
> >> To: eugenebi at hotmail.com
> >> CC: jingham at apple.com; lldb-dev at lists.llvm.org
> >>
> >> So I have made a small test program (which does nothing but spin in a
> >> loop), and indeed it is the SIGHUP that kills it after detach. If the
> >> test program blocks the signal, then it continues running even after
> >> detach:
> >> $ cat a.c
> >> #include <unistd.h>
> >> #include <signal.h>
> >>
> >> int main() {
> >> signal(SIGHUP, SIG_IGN);
> >> for (;;) sleep(1);
> >> }
> >> $ cc a.c -g
> >> $ ps -A | grep a.out
> >> $ ~/ll/build/dbg/bin/lldb ./a.out
> >> (lldb) target create "./a.out"
> >> Current executable set to './a.out' (x86_64).
> >> (lldb) b 6
> >> Breakpoint 1: where = a.out`main + 19 at a.c:6, address =
> >> 0x0000000000400590
> >> (lldb) r
> >> Process 13416 launched: './a.out' (x86_64)
> >> Process 13416 stopped
> >> * thread #1: tid = 13416, 0x0000000000400590 a.out`main + 19 at a.c:6,
> >> name = 'a.out', stop reason = breakpoint 1.1
> >> frame #0: 0x0000000000400590 a.out`main + 19 at a.c:6
> >> 3
> >> 4 int main() {
> >> 5 signal(SIGHUP, SIG_IGN);
> >> -> 6 for (;;) sleep(1);
> >> 7 }
> >> (lldb) detach
> >> Process 13416 detached
> >> (lldb) q
> >> $ ps -A | grep a.out
> >> 13416 ? 00:00:00 a.out
> >>
> >>
> >> On 29 March 2016 at 18:38, Eugene Birukov <eugenebi at hotmail.com> wrote:
> >> > I believe this is not SIGHUP on debugger exit. I am using my own C++
> >> > program
> >> > that calls into LLDB API. So, this program is still alive after calling
> >> > SBProcess::Detach() but the target dies. Also, the target intercepts
> >> > SIGHUP
> >> > to do cleanup before exiting. I put printf there, it was not hit.
> >> The fact whether your program is alive irrelevant. What matters is
> >> that by cleaning up the process structure, we will also close the
> >> master end of the pty used for inferior communication, and this is
> >> what causes the SIGHUP. For that reason you also cannot use a printf
> >> to do diagnostics as the output has nowhere to go. Note that lldb's
> >> behavior here will be different from gdb as gdb does not do stdio
> >> redirection, and has the inferior share the pty with the debugger (in
> >> which case your program will die when you close the terminal window).
> >>
> >> >
> >> > I tried interactive LLDB, the target is not there:
> >> >
> >> > Process 49145 stopped
> >> > * thread #1: tid = 49145, ..., stop reason = signal SIGSTOP
> >> > frame #0: 0x00007ffff6a5bbed libc.so.6 at syscall-template.S:81
> >> > (lldb) detach
> >> > Process 49145 detached
> >> > (lldb) q
> >> > eugene at EUGENEBI-L1:~/tmp$ ps
> >> > PID TTY TIME CMD
> >> > 30714 pts/17 00:00:00 bash
> >> > 49259 pts/17 00:00:00 ps
> >> Note that the inferior will not show up here even if it exists, as ps
> >> will only list the processes with the same tty, but at this point the
> >> inferior process has no tty.
> >>
> >> Good luck with your investigations.
> >>
> >> pl
> >
> > _______________________________________________ lldb-dev mailing list
> > lldb-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev

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