From: Michael Snyder <msnyder@specifix.com>
To: Vladimir Prus <ghost@cs.msu.su>
Cc: gdb@sources.redhat.com
Subject: Re: Questionable breakpoint stepping code
Date: Mon, 26 Nov 2007 19:01:00 -0000 [thread overview]
Message-ID: <1196102967.2501.29.camel@localhost.localdomain> (raw)
In-Reply-To: <fi6m64$qav$1@ger.gmane.org>
On Fri, 2007-11-23 at 16:56 +0300, Vladimir Prus wrote:
> The infrun.c:handle_inferiour_event function has
> this code block:
>
> if (thread_hop_needed)
> {
> ........
> remove_status = remove_breakpoints ();
> /* Did we fail to remove breakpoints? If so, try
> to set the PC past the bp. (There's at least
> one situation in which we can fail to remove
> the bp's: On HP-UX's that use ttrace, we can't
> change the address space of a vforking child
> process until the child exits (well, okay, not
> then either :-) or execs. */
> if (remove_status != 0)
> {
> /* FIXME! This is obviously non-portable! */
> write_pc_pid (stop_pc + 4, ecs->ptid);
> /* We need to restart all the threads now,
> * unles we're running in scheduler-locked mode.
> * Use currently_stepping to determine whether to
> * step or continue.
> */
> /* FIXME MVS: is there any reason not to call resume()? */
> if (scheduler_mode == schedlock_on)
> target_resume (ecs->ptid,
> currently_stepping (ecs), TARGET_SIGNAL_0);
> else
> target_resume (RESUME_ALL,
> currently_stepping (ecs), TARGET_SIGNAL_0);
> prepare_to_wait (ecs);
> return;
> }
>
> The code is a bit scary -- specifically I sure don't want GDB to mess
> with PC values like this on x86, if removing breakpoints fails in any way.
> The essential bits of this code are present as of revision 1.1 of infrun.c
> (added in 1999).
>
> So:
> 1. Anybody knows if this code is still needed for modern HPUX?
> 2. Can we have it wrapped in #ifdef, and if so, which one?
>
> - Volodya
Hi Volodya,
I think it's my code. It's not really related specifically
to HPUX, that comment was there in the previous iteration and
I just kept it.
The several state variables with "thread_hop" as part of their
names are related to single-stepping in the presence of thread-
specific breakpoints. They are meant to solve the problem of
what to do if you are doing a step, and you hit a thread-specific
breakpoint, but with the wrong thread.
You need to do a kind of special single-step to get past that
particular breakpoint, then return to the single-stepping
infrun state.
As for the scheduler-locking code, that pertains to a
different but not wholly unrelated functionality (set
scheduler-locking), which affects which threads can run
at which times.
As for your last question, no, I don't believe we approve
of ifdefs...
Cheers,
Michael
next prev parent reply other threads:[~2007-11-26 19:01 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-23 14:06 Vladimir Prus
2007-11-26 19:01 ` Michael Snyder [this message]
2007-11-26 19:16 ` Vladimir Prus
2007-11-26 19:24 ` Daniel Jacobowitz
2007-11-26 19:28 ` Michael Snyder
2007-11-27 13:50 ` Vladimir Prus
2007-11-27 13:54 ` Daniel Jacobowitz
2007-11-27 19:33 ` Joel Brobecker
2007-11-29 12:35 ` Vladimir Prus
2007-11-30 1:14 ` Joel Brobecker
2007-11-30 11:48 ` Vladimir Prus
2007-12-13 16:09 ` Vladimir Prus
2008-01-17 1:13 ` Jim Blandy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1196102967.2501.29.camel@localhost.localdomain \
--to=msnyder@specifix.com \
--cc=gdb@sources.redhat.com \
--cc=ghost@cs.msu.su \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).