From: Daniel Jacobowitz <dan@codesourcery.com>
To: Ulrich Weigand <uweigand@de.ibm.com>
Cc: Ken Werner <ken@linux.vnet.ibm.com>,
gdb-patches@sourceware.org,
Joel Brobecker <brobecker@adacore.com>,
Vladimir Prus <vladimir@codesourcery.com>
Subject: Re: [patch] fix pre-/post- in-/decrement
Date: Tue, 05 Oct 2010 13:42:00 -0000 [thread overview]
Message-ID: <20101005134200.GJ6985@caradoc.them.org> (raw)
In-Reply-To: <201010051328.o95DSJ8L027985@d12av02.megacenter.de.ibm.com>
On Tue, Oct 05, 2010 at 03:28:19PM +0200, Ulrich Weigand wrote:
> Daniel Jacobowitz wrote:
> > On Tue, Oct 05, 2010 at 01:24:51AM +0200, Ulrich Weigand wrote:
> > > - If you execute "set *$p = *$q = 0" and the write to *$q fails,
> > > do you really expect *$p to be set to the old value of *$q
> > > instead of to 0?
> >
> > Yes, I would expect that. To me, this is roughly "the debugger treats
> > all pointers as volatile".
>
> The thing is, I had interpreted the C standard to read that even if
> pointers p and q *are* volatile, a statement like "*p = *q = 0" would
> still just trigger two writes, and no reads.
You're right, I remember Nathan's recent arguments about this on
gcc-patches.
> "Assignments are also expressions and have an rvalue. However when assigning
> to a scalar volatile, the volatile object is not reread, regardless of whether
> the assignment expression's rvalue is used or not. If the assignment's rvalue
> is used, the value is that assigned to the volatile object. [...] If you need
> to read the volatile object after an assignment has occurred, you must use a
> separate expression with an intervening sequence point."
> To reduce the potential for confusion, it seems to me GDB ought to mirror
> that behavior as well ...
Hmm.
It seems to me that this is a disruptive change for us, because the "a
= b" case is more likely to be used than anything fancy (a += b, a = b
= c). If we change it, we should document the change.
Vladimir, would this interact with your recent varobj changes? We
worked out exactly which reads we wanted, but I don't remember if
value_assign is involved.
--
Daniel Jacobowitz
CodeSourcery
next prev parent reply other threads:[~2010-10-05 13:42 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-17 12:58 [patch] GNU vector unop support Ken Werner
2010-09-28 16:04 ` Ken Werner
[not found] ` <20100930185634.GC6213@adacore.com>
2010-10-01 17:45 ` [patch] fix pre-/post- in-/decrement Ken Werner
2010-10-04 13:01 ` Ulrich Weigand
2010-10-04 19:47 ` Ken Werner
2010-10-04 20:45 ` Daniel Jacobowitz
2010-10-04 21:58 ` Ulrich Weigand
2010-10-04 22:59 ` Daniel Jacobowitz
2010-10-04 23:25 ` Ulrich Weigand
2010-10-05 1:17 ` Daniel Jacobowitz
2010-10-05 13:28 ` Ulrich Weigand
2010-10-05 13:42 ` Daniel Jacobowitz [this message]
2010-10-06 18:59 ` [rfc] Fix value_assign return value (Re: [patch] fix pre-/post- in-/decrement) Ulrich Weigand
2010-10-26 13:42 ` Daniel Jacobowitz
2010-12-01 16:51 ` Ulrich Weigand
2010-10-06 20:55 ` [patch] fix pre-/post- in-/decrement Vladimir Prus
2010-10-07 12:38 ` Ken Werner
2010-10-12 23:00 ` Tom Tromey
2010-10-13 8:45 ` Andreas Schwab
2010-10-13 9:23 ` Ken Werner
2010-10-13 16:07 ` Daniel Jacobowitz
2010-10-13 19:01 ` Tom Tromey
2010-10-19 7:38 ` Ken Werner
2010-11-02 8:23 ` Ken Werner
2010-11-02 20:31 ` Tom Tromey
2010-11-03 13:52 ` Ken Werner
2010-10-04 20:52 ` [patch] GNU vector unop support Ken Werner
2010-10-06 23:27 ` Joel Brobecker
2010-10-07 16:23 ` Ken Werner
2010-11-03 14:07 ` Ken Werner
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