Messages in this thread | | | From | Pavel Labath <> | Date | Wed, 18 Nov 2015 10:10:40 +0000 | Subject | Re: ptrace and pseudoterminals |
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On 5 November 2015 at 20:29, Peter Hurley <peter@hurleysoftware.com> wrote: > On 11/05/2015 01:35 PM, Pavel Labath wrote: >> That said, it seems to me that this could be a generally useful >> feature. For the test suite, I can insert a sleep (even a large one, >> to be sure), but this seems like a sub-optimal solution for general >> debugger operation. E.g., when we want to display all tracee output(*) >> before we print out the debugger prompt, we don't know if the tracee >> has written anything, and we would need to sleep always, just in case >> it has done that. > > My comment suggesting re-select()ing was aimed at the test suite only. > > For the debugger, I would always mixin new output from the target > regardless of when it arrived. But feel free to ignore my unsolicited > design advice :) ;)
> > >> This is especially tricky for remote debugging, as >> the current gdb-remote protocol does not allow sending stdio after the >> stop notification. > > Hmm, I could swear I've seen gdb scrolling away with new output while > stopped. That's quite possible if this wasn't a remote session. Gdb shares the terminal with the tracee, so the order the output comes out really depends on the internal terminal implementation. In lldb, we create a new pty for the tracee and control the output forwarding ourselves.
If it was a remote session than I would be very interested in it as I don't think the remote protocol supports that.
> >> So, I actually quite like the fsync() idea, but I >> don't know if this is something that would be generally accepted (?). > > Let me think more on this; maybe I can come up with a way to trip it > within an existing method.
Thanks. I have not seen this occurring since, I contacted you, so it's not a big priority for me now, but I may revisit it later.
>> A side question: When I replace the pty with a pipe, the data seems to >> be delivered immediately. Is this something that is guaranteed, or >> this happens to work only accidentally and could change in the future >> (e.g. by moving the pipe processing to a kworker process or whatever)? > > I would think the existing pipe behavior is more or less guaranteed, since > pipes are commonly used for process synchronization. That's good to know, thanks. :)
cheers, pl
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