Date: Thu, 14 Jul 2016 11:16:05 -0700 From: Mark Johnston <markj@FreeBSD.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-current@FreeBSD.org Subject: Re: ptrace attach in multi-threaded processes Message-ID: <20160714181605.GA17310@wkstn-mjohnston.west.isilon.com> In-Reply-To: <20160714052537.GZ38613@kib.kiev.ua> References: <20160712170502.GA71220@wkstn-mjohnston.west.isilon.com> <20160712175150.GP38613@kib.kiev.ua> <20160712182414.GC71220@wkstn-mjohnston.west.isilon.com> <20160713033036.GR38613@kib.kiev.ua> <20160713040210.GA89573@wkstn-mjohnston.west.isilon.com> <20160713045439.GT38613@kib.kiev.ua> <20160713164247.GA2066@wkstn-mjohnston.west.isilon.com> <20160713191947.GW38613@kib.kiev.ua> <20160713200139.GC2066@wkstn-mjohnston.west.isilon.com> <20160714052537.GZ38613@kib.kiev.ua>
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On Thu, Jul 14, 2016 at 08:25:37AM +0300, Konstantin Belousov wrote: > On Wed, Jul 13, 2016 at 01:01:39PM -0700, Mark Johnston wrote: > > On Wed, Jul 13, 2016 at 10:19:47PM +0300, Konstantin Belousov wrote: > > > Hmm, I think no, we can not make such change. Issue is, debugger > > > interface guarantees (at least for single-threaded programs it is > > > done correctly) that SIGSTOP is noted. In my opinion, it would be the > > > incompatible API change. > > > > But this guarantee is not honoured in the single-threaded case where > > PT_ATTACH sends SIGSTOP after another signal is already pending. This > > other signal will stop the process in ptracestop(), so SIGSTOP will not > > be reported until after a PT_CONTINUE or PT_DETACH, which seems to > > violate the interface as you described it. Am I missing some reason > > that this cannot occur? If not, I'll write a test case for the > > single-threaded case first. > > Please give me some initial test case, I am fine with single-threaded case. > I do not think that the mt test would be much different ? Please see the program here: https://people.freebsd.org/~markj/ptrace_stop.c It cheats a bit: it uses SIGSTOP to stop the child before sending a SIGHUP to it. However, this is just for convenience; note that PT_ATTACH will result in a call to thread_unsuspend() on the child, so PT_ATTACH's SIGSTOP will be delivered to a running process. When ptrace attaches, the child stops and WSTOPSIG(status) == SIGHUP. When ptrace detaches, the child is left stopped.
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