[PATCH] USE_SEIZE: fix detaching from stopped processes

[Dmitry V. Levin]

On Wed, Jun 19, 2013 at 12:36:20AM +0400, Dmitry V. Levin wrote:
> On Tue, Jun 18, 2013 at 06:18:14PM +0200, Denys Vlasenko wrote:
> > * strace.c (detach) [USE_SEIZE]: If PTRACE_SEIZE API is in use, stop
> > the tracee using PTRACE_INTERRUPT instead of sending it a SIGSTOP.
> > In a subsequent waitpid loop, wait for either SIGSTOP or SIGTRAP.
[...]
> > @@ -810,7 +819,9 @@ detach(struct tcb *tcp)
> >  				/* Au revoir, mon ami. */
> >  				break;
> >  			}
> > -			if (WSTOPSIG(status) == SIGSTOP) {
> > +			if (WSTOPSIG(status) == SIGSTOP
> > +			 || WSTOPSIG(status) == SIGTRAP /* may be generated by PTRACE_INTERRUPT stop */
> > +			) {
> 
> In case of PTRACE_INTERRUPT this WSTOPSIG(status) is not plain SIGTRAP
> but (SIGTRAP | 0x80), which also may happen in other !use_seize cases.
> That is, the right check seems to be
> 	WSTOPSIG(status) == SIGSTOP ||
> 	(use_seize && WSTOPSIG(status) == (SIGTRAP | 0x80))
> It also passes both tests/detach-sleeping and tests/detach-stopped.

It still hangs while detaching from a running process
(just added tests/detach-running fails).  What seems to work so far is
 	WSTOPSIG(status) == SIGSTOP ||
	(use_seize && (WSTOPSIG(status) & 0x7f) == SIGTRAP)


-- 
ldv
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