From: "Ulrich Weigand" <uweigand@de.ibm.com>
To: pedromfc@linux.ibm.com (Pedro Franco de Carvalho)
Cc: gdb-patches@sourceware.org
Subject: Re: [PATCH 3/3] [PowerPC] Fix debug register issues in ppc-linux-nat
Date: Fri, 09 Aug 2019 11:04:00 -0000 [thread overview]
Message-ID: <20190809110434.C48D2D80277@oc3748833570.ibm.com> (raw)
In-Reply-To: <875zn7iery.fsf@linux.ibm.com> from "Pedro Franco de Carvalho" at Aug 08, 2019 05:27:29 PM
Pedro Franco de Carvalho wrote:
> "Ulrich Weigand" <uweigand@de.ibm.com> writes:
>
> > This looks generally good to me, just two questions:
> >
> > - As mentioned in the 1/3 patch, why do you need the low_new_clone
> > callback? As I understand it, you'll get low_new_thread called
> > immediatedly afterwards, which will mark the thread as "stale",
> > and once it is scheduled again, all debug regs will be set up
> > from scratch anyway ...
>
> The reason I did this is so that we have the lwp object of the parent
> thread, so that we can copy the correct debug register state. The
> arguments for low_new_thread don't include the parent. I think other
> targets always know how to clear all the debug registers without keeping
> track of anything, but we need to know which slots might already be
> installed in a new thread.
I may still be missing something, but why exactly *do* we need to know
which slots might already be installed? I'd have assumed that when we
get to low_prepare_to_resume, and the lwp is marked stale, we just throw
away everything and install the complete desired state.
> Another reason is that add_lwp (and therefore low_new_thread) is also
> called in cases other than a ptrace clone event.
Well, yes, but those cases *also* need to be handled, right? This is
e.g. when you attach to an already multi-threaded process while there
are already watchpoints set up. In that case, you'll need to install
those watchpoints into all those threads.
> > - We currently do not support hardware watchpoints in gdbserver,
> > even though we really should. Ideally, the low-level code to
> > handle debug regs should be shared between gdb and gdbserver,
> > as is done e.g. on x86. Now, I'm not saying that handling
> > gdbserver is a pre-req for this patch (fixing GDB first is of
> > course fine!), but I'm wondering if it would make sense, given
> > that you're refactoring a lot of this code anyway, to think
> > about whether this setup would help or hinder a future merge
> > with gdbserver.
>
> Ok, I'll review this and see if this can be easily ported to gdbserver.
Thanks!
Bye,
Ulrich
--
Dr. Ulrich Weigand
GNU/Linux compilers and toolchain
Ulrich.Weigand@de.ibm.com
next prev parent reply other threads:[~2019-08-09 11:04 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-26 12:50 [PATCH 0/3] low_new_clone in linux-nat.c and powerpc watchpoint fixes Pedro Franco de Carvalho
2019-07-26 12:50 ` [PATCH 1/3] Add low_new_clone method to linux_nat_target Pedro Franco de Carvalho
2019-08-08 14:05 ` Ulrich Weigand
2019-07-26 12:50 ` [PATCH 2/3] [PowerPC] Move up some register access routines Pedro Franco de Carvalho
2019-08-08 16:25 ` Ulrich Weigand
2019-07-26 12:50 ` [PATCH 3/3] [PowerPC] Fix debug register issues in ppc-linux-nat Pedro Franco de Carvalho
2019-08-08 16:24 ` Ulrich Weigand
2019-08-08 20:27 ` Pedro Franco de Carvalho
2019-08-09 11:04 ` Ulrich Weigand [this message]
2019-08-09 15:04 ` Pedro Franco de Carvalho
2019-08-09 15:28 ` Ulrich Weigand
2019-08-09 15:53 ` Pedro Franco de Carvalho
2019-08-13 13:50 ` Pedro Franco de Carvalho
2019-08-21 15:31 ` Ulrich Weigand
2019-08-21 17:45 ` Pedro Franco de Carvalho
2019-08-22 10:27 ` Ulrich Weigand
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