From: Daniel Jacobowitz <drow@false.org>
To: Eli Zaretskii <eliz@gnu.org>
Cc: Johan Rydberg <jrydberg@virtutech.com>,
dan@shearer.org, gdb@sources.redhat.com
Subject: Re: [discuss] Support for reverse-execution
Date: Fri, 20 May 2005 13:14:00 -0000 [thread overview]
Message-ID: <20050520131348.GB25206@nevyn.them.org> (raw)
In-Reply-To: <01c55d27$Blat.v2.4$69471120@zahav.net.il>
Disclaimer: I have not looked at the code at all; I want to get the
copyright assignment rolling first.
On Fri, May 20, 2005 at 01:32:47PM +0300, Eli Zaretskii wrote:
> > To implement "rnext" I had to add a new target-specific function that
> > tries to figure out the address of the call instruction based on the
> > last executed instruction and the instruction to be executed, IF the
> > current instruction can be identified as a return insn.
Johan, when I sketched out some algorithms for implementing these
commands, I got the feeling that this was not a good way to do it.
There are just too many ways to jump, and they can be pretty tricky to
recognize on some architectures. PowerPC is easy, but it's a little
more complicated to disassemble starting from the end of an instruction
on ia32. Here's another one that requires absolutely no target support:
- Detect reverse-step into a function
- Set breakpoints at all entry points of the function; GDB doesn't
support multiple entry points yet, really, so a breakpoint at
the first instruction and a big fat comment is all this takes.
- When you hit an entry point breakpoint, reverse-step once more.
- If you have entered a different function, for instance via a
reversed tail call, and you can still see the desired frame
on the stack, then repeat.
i.e. build reverse-next on top of reverse-finish. reverse-finish
should take you to the intermediate caller in a tail call situation,
not to the previous frame on the stack.
Of course neither algorithm is robust in the case of stray jumps.
Bookmarks and single-steps for that are the best we're going to get.
> > + add_com ("rnext", class_run, rnext_command,
> > + "Step program until it reaches the previous source line.\n\
>
> "Go backwards until the program reaches the source line before the
> current one."
Johan used previous, you used backwards; let's figure out what we're
calling the commands first :-P
> > + add_com_alias ("rn", "rnext", class_run, 1);
>
> Do we want another alias called "previous"?
I have no objection.
> I'd prefer that target_resume accepted the direction argument. Is
> there something that I'm missing that makes this hard or impossible?
It should either be an argument, or a separate target hook as Michael
proposed. No existing target supports it, so it would save us updating
all targets to reject it. Which is just mechanical, so I don't feel
strongly either way.
--
Daniel Jacobowitz
CodeSourcery, LLC
next prev parent reply other threads:[~2005-05-20 13:14 UTC|newest]
Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-05-19 1:23 Dan Shearer
2005-05-19 13:01 ` Johan Rydberg
2005-05-19 13:18 ` Daniel Jacobowitz
2005-05-19 13:47 ` Johan Rydberg
2005-05-20 10:37 ` Eli Zaretskii
2005-05-20 11:37 ` Andreas Schwab
2005-05-20 13:18 ` Daniel Jacobowitz
2005-05-20 13:36 ` Fabian Cenedese
2005-05-20 13:47 ` Daniel Jacobowitz
2005-05-20 14:41 ` Eli Zaretskii
2005-05-20 22:14 ` Daniel Jacobowitz
2005-05-20 12:22 ` Johan Rydberg
2005-05-20 13:19 ` Daniel Jacobowitz
2005-05-20 14:12 ` Eli Zaretskii
2005-05-20 13:14 ` Daniel Jacobowitz [this message]
2005-05-20 14:34 ` Eli Zaretskii
2005-05-20 15:40 ` Johan Rydberg
2005-05-20 10:47 ` Eli Zaretskii
-- strict thread matches above, loose matches on Subject: below --
2005-05-21 15:53 Paul Schlie
2005-05-20 22:11 Michael Snyder
2005-05-20 23:32 ` Paul Schlie
2005-05-20 21:59 Michael Snyder
2005-05-20 21:51 Michael Snyder
2005-05-21 9:44 ` Eli Zaretskii
2005-05-20 21:44 Michael Snyder
2005-05-20 21:25 Michael Snyder
2005-05-20 21:16 Michael Snyder
2005-05-20 21:31 ` Daniel Jacobowitz
2005-05-21 9:39 ` Eli Zaretskii
2005-05-23 18:19 ` Michael Snyder
2005-05-20 21:11 Michael Snyder
2005-05-20 21:27 ` Daniel Jacobowitz
2005-05-20 19:02 Michael Snyder
2005-05-20 20:43 ` Eli Zaretskii
2005-05-20 21:03 ` Michael Snyder
2005-05-20 15:49 Paul Schlie
2005-05-20 17:41 ` Dan Shearer
2005-05-20 22:01 ` Paul Schlie
2005-05-20 22:08 ` Daniel Jacobowitz
2005-05-20 22:43 ` Paul Schlie
2005-05-21 0:58 ` Daniel Jacobowitz
2005-05-21 1:42 ` Paul Schlie
2005-05-21 1:53 ` Daniel Jacobowitz
2005-05-21 1:56 ` Daniel Jacobowitz
2005-05-21 15:03 ` Paul Schlie
2005-05-21 14:13 ` Paul Schlie
2005-05-21 14:23 ` Daniel Jacobowitz
2005-05-21 15:04 ` Paul Schlie
2005-05-20 20:58 ` Michael Snyder
2005-05-20 21:35 ` Paul Schlie
2005-05-16 17:47 Dan Shearer
2005-05-16 18:04 ` Dan Shearer
2005-05-20 18:15 ` Daniel Jacobowitz
2005-05-21 0:05 ` Frank Ch. Eigler
2005-05-21 10:13 ` Eli Zaretskii
2005-05-21 10:28 ` Russell Shaw
2005-05-21 12:38 ` Eli Zaretskii
2005-05-21 12:55 ` Russell Shaw
2005-05-21 14:39 ` Russell Shaw
2005-05-21 14:19 ` Daniel Jacobowitz
2005-05-21 15:46 ` Eli Zaretskii
2005-05-21 17:43 ` Daniel Jacobowitz
2005-05-23 19:39 ` Dan Shearer
2005-05-12 23:08 Michael Snyder
2005-05-13 6:23 ` Eli Zaretskii
2005-05-19 13:46 ` Daniel Jacobowitz
2005-05-19 18:46 ` Michael Snyder
2005-05-19 19:26 ` Johan Rydberg
2005-05-20 10:55 ` Eli Zaretskii
2005-05-20 13:04 ` Daniel Jacobowitz
2005-05-20 14:30 ` Eli Zaretskii
2005-05-20 14:43 ` Andreas Schwab
2005-05-20 20:48 ` Michael Snyder
2005-05-20 20:51 ` Daniel Jacobowitz
2005-05-20 20:38 ` Michael Snyder
2005-05-20 15:05 ` Vladimir Prus
2005-05-20 15:58 ` Eli Zaretskii
2005-05-20 18:14 ` Daniel Jacobowitz
2005-05-20 18:30 ` Eli Zaretskii
2005-05-20 19:27 ` Stan Shebs
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