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Re: [RFC] Don't allow setting register in non-innermost frame
- From: Jan Kratochvil <jan dot kratochvil at redhat dot com>
- To: Yao Qi <yao at codesourcery dot com>
- Cc: Tom Tromey <tromey at redhat dot com>, Doug Evans <dje at google dot com>, gdb-patches at sourceware dot org
- Date: Mon, 10 Sep 2012 09:46:39 +0200
- Subject: Re: [RFC] Don't allow setting register in non-innermost frame
- References: <1345170040-25959-1-git-send-email-yao@codesourcery.com> <CADPb22SGp-9TaoA3rNi_PJordCuv_bjwFQZiHvfjktHx3Y_krA@mail.gmail.com> <87hartpodt.fsf@fleche.redhat.com> <20120907164544.GA18234@host2.jankratochvil.net> <504D49DA.6070006@codesourcery.com>
On Mon, 10 Sep 2012 04:00:58 +0200, Yao Qi wrote:
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/set-reg.c
[...]
> +main (int argc, char **argv)
Two spaces.
[...]
> --- a/gdb/valops.c
> +++ b/gdb/valops.c
> @@ -1241,6 +1241,22 @@ value_assign (struct value *toval, struct value *fromval)
> and then restore the new frame afterwards. */
> old_frame = get_frame_id (deprecated_safe_get_selected_frame ());
>
> + /* TOVAL is a register, although VALUE_LVAL(TOVAL) may not be
GNU formatting applies also to comments: VALUE_LVAL (TOVAL)
> + lval_register. A call-saved register saved in memory will have
> + 'VALUE_REGNUM >= 0' but 'VALUE_LVAL == lval_memory'. We also have to
> + avoid emitting warning when assign value to some local variables which
> + are stored in registers, TYPE_OBJFILE_OWNED helps to differentiate
> + we are assigning to a register explicitly or to a variable saved in
> + register. */
> + if (VALUE_REGNUM (toval) >= 0 && !TYPE_OBJFILE_OWNED (type))
There should be a better comment at value->regnum:
/* Register number if the value is from a register. */
short regnum;
as currently it looks to me that value->regnum is not defined for
value->lval != lval_register
This your patch IMO exploits side-effect behavior of value_of_register
function implementation, it would be good to document we depend now on this
REGNUM meaning in both value->regnum and in value_of_register.
> + {
> + /* Figure out which frame this is in currently. */
> + struct frame_info *frame = frame_find_by_id (VALUE_FRAME_ID (toval));
> +
> + if (get_next_frame (frame) != NULL)
This is not safe, I do not have a countercase reproducer but in general
frame_find_by_id can return NULL and even the code below checks for it:
case lval_register:
[...]
frame = frame_find_by_id (VALUE_FRAME_ID (toval));
[...]
if (!frame)
error (_("Value being assigned to is no longer active."));
Something could call reinit_frame_cache in the meantime (see the issues from
PR 13866) and then frame_ids may become stale.
Either put there also the error check/call or I would find easier:
if (frame_relative_level (frame) == 0)
> + warning (_("Assigning to register in non-innermost frame."));
Are you / other people really against a query() here?
This way if one does the non-zero frame assignment it will print the warning.
User says oops, I did not want to do it - but the damage has been already
done, unintended memory is overwritten and there is no way back.
I was suggesting something like:
if (!query (_("Really assign to stored register in non-innermost frame? ")))
error (_("Not confirmed."));
I understand you are more concerned with MI but if I read correctly MI will
answer it as 'y', unaware whether the query message gets propagated to your MI
frontend so maybe you would like:
if (query (_("Really assign to stored register in non-innermost frame? ")))
warning (_("Assigning to register in non-innermost frame."));
else
error (_("Not confirmed."));
> + }
> +
> switch (VALUE_LVAL (toval))
> {
> case lval_internalvar:
> --
> 1.7.7.6
Thanks,
Jan