From: Joel Brobecker <brobecker@adacore.com>
To: David Taylor <dtaylor@emc.com>
Cc: Stan Shebs <stanshebs@earthlink.net>,
"gdb-patches@sourceware.org" <gdb-patches@sourceware.org>
Subject: Re: two agent expression nits (one line each)
Date: Sat, 20 Dec 2014 17:19:00 -0000 [thread overview]
Message-ID: <20141220171955.GG12884@adacore.com> (raw)
In-Reply-To: <23074.1418658035@usendtaylorx2l>
Hi David,
> > Would you mind taking care of that for us? I kept that message around
> > in the hope that I'd have a clearer picture with a little extra time,
> > but I am still not sure whether you're just suggesting a documentation
> > fix, or if you're saying we should fix the implementation...
>
> The first part is pure documentation -- the description is correct but
> the summary line is wrong. The second part is implementation -- the
> consumed and produced fields are used to check for stack underflow and
> overflow.
>
> The fields are used by gdb and gdbserver for sanity checking the
> bytecode expression -- checking for underflow and overflow.
>
> The underflow check catches bad bytecode sequences generated by GDB.
>
> Since DEFOP has consumed as 0 when it is really 1, that means that GDB
> will think that there is more on the stack than there really is.
>
> So, if GDB generates a bytecode sequence that underflows it might not
> catch it. It does not currently generate bad sequences, so fixing it
> will merely help catch future lossage.
>
> As I recall, the overflow check is used by gdbserver to verify that it
> has sufficent stack space for the expression. The bad DEFOP line makes
> it think that the expression is using one more stack slot than reality.
> But, gdbserver has fairly generous bytecode stack space -- so unless the
> expression is really complicated, that won't happen.
Since you understand what should be done, would you mind sending
a patch in for Stan to review?
--
Joel
next prev parent reply other threads:[~2014-12-20 17:19 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-11 17:54 David Taylor
2014-11-23 3:27 ` Joel Brobecker
2014-12-02 20:45 ` Stan Shebs
2014-12-13 13:44 ` Joel Brobecker
2014-12-15 15:41 ` David Taylor
2014-12-20 17:19 ` Joel Brobecker [this message]
2015-02-03 21:58 ` David Taylor
2015-02-11 7:49 ` Joel Brobecker
2015-02-11 17:28 ` Stan Shebs
2015-02-13 19:21 ` David Taylor
2015-02-20 3:05 ` pushed (master+branch): " Joel Brobecker
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