This is the mail archive of the
gdb-patches@sourceware.org
mailing list for the GDB project.
Re: [RFC 5/5] uprobes: add global breakpoints
- From: Sebastian Andrzej Siewior <bigeasy at linutronix dot de>
- To: Oleg Nesterov <oleg at redhat dot com>
- Cc: linux-kernel at vger dot kernel dot org, x86 at kernel dot org, Peter Zijlstra <a dot p dot zijlstra at chello dot nl>, Arnaldo Carvalho de Melo <acme at ghostprotocols dot net>, Roland McGrath <roland at redhat dot com>, Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>, Ananth N Mavinakaynahalli <ananth at in dot ibm dot com>, stan_shebs at mentor dot com, gdb-patches at sourceware dot org
- Date: Tue, 14 Aug 2012 13:43:56 +0200
- Subject: Re: [RFC 5/5] uprobes: add global breakpoints
- References: <1344355952-2382-1-git-send-email-bigeasy@linutronix.de> <1344355952-2382-6-git-send-email-bigeasy@linutronix.de> <20120808131457.GA5309@redhat.com> <20120809171802.GB27835@linutronix.de> <20120813131623.GA5269@redhat.com>
On 08/13/2012 03:16 PM, Oleg Nesterov wrote:
On 08/09, Sebastian Andrzej Siewior wrote:
* Oleg Nesterov | 2012-08-08 15:14:57 [+0200]:
What I miss right now is an interface to tell the user/gdb that there is a
program that hit a global breakpoint and is waiting for further instructions.
A "tail -f trace" does not work and may contain also a lot of other
informations. I've been thinking about a poll()able file which returns pids of
tasks which are put on hold. Other suggestions?
Honestly, I am not sure this is that useful...
How would you notify gdb that there is a new task that hit a breakpoint?
Or learn yourself?
But why do we need this?
Shouldn't we learn somehow that a process hits a breakpoint? The task
was not yet monitored by gdb.
OK, you do not need to convince me, I try to never argue with
new features.
If there is a simple mechanism, I would switch to it. Right now I think
about using this "notification mechanism" to auto-exlude the listener
(and its parents) from the list of possible targets. So I don't freeze
the whole system while I have a breakpoint at malloc() in libc.
However, I certainly dislike TASK_TRACED in uprobe_wait_traced().
And sleeping in ->handler() is not fair to other consumers.
I added it as the last task in current consumer. I could move it out of
the consumer loop and freeze it after all consumer are handled but then
I lose the filter member (which is currently NULL, I know).
And I do not think you should modify ptrace_attach() at all.
gdb/user can wakeup the task after PTRACE_ATTACH itself.
I see. gdb / strace --pid $num" gdb does PTRACE_ATTACH and waits
afterwords in wait() indefinitely for the SIGSTOP which is blocked
since the process is already in TASK_TRACED. This is nice since the
signals are blocked and are delivered once the task is unfrozed.
Oleg.
Sebastian