linux-kernel - Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after PTRACE

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Date:	Wed, 23 Feb 2011 17:44:27 +0100
From:	Jan Kratochvil <jan.kratochvil@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Tejun Heo <tj@...nel.org>, Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after
 PTRACE_ATTACH

On Mon, 21 Feb 2011 15:23:25 +0100, Oleg Nesterov wrote:
> On 02/20, Jan Kratochvil wrote:
> > Now if new GDB should allow inferior functions calls on previously
> > `(T) stopped' process doing PTRACE_CONT(SIGCONT)
> 
> No, no, this won't work. You need to send SIGCONT via kill/tkill. Once
> again, we can add the special case for PTRACE_CONT(SIGCONT), but please
> look at Roland's comment: http://marc.info/?l=linux-kernel&m=129796917823181
> 
> And given that currently gdb does PTRACE_CONT(0) this special case can't
> help anyway unless you change gdb.

I would better play with a patched kernel.


> > but how to make it `(T) stopped' afterwards?  PTRACE_CONT(SIGSTOP)
> > right after the inferior call will make the old kernels run the inferior - we
> > do not want that.
> 
> Hmm... probably I am totally confused... but PTRACE_CONT(SIGSTOP)
> should work in this case, the tracee reports SIGTRAP after the single-step
> (if I understand correctly how gdb implements this).

The inferior call returns to a breakpoint (0xcc), this is the reason of the
SIGTRAP at the end.  I expect PTRACE_CONT(SIGSTOP) could work even in such
case.


Thanks,
Jan
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