RE: PRecord sets memory even when it says it did not

Marc Khouzam
2009-09-14T17:10:47Z

> -----Original Message-----
> From: Hui Zhu [mailto:teawater@gmail.com]
> Sent: Monday, September 14, 2009 12:15 PM
> To: Daniel Jacobowitz; Marc Khouzam; gdb@sourceware.org;
> Michael Snyder; gdb-patches ml
> Subject: Re: PRecord sets memory even when it says it did not
>
> On Mon, Sep 14, 2009 at 23:53, Daniel Jacobowitz
> <drow@false.org> wrote:
> > On Mon, Sep 14, 2009 at 12:39:35PM +0800, Hui Zhu wrote:
> >> > (gdb) set var a = 8
> >> > Because GDB is in replay mode, writing to memory will
> make the execution log unusable from this point onward.
> Write memory at address 0xbffff6a0?(y or [n]) n
> >> > Process record canceled the operation.
> >> > (gdb) p a
> >> > $2 = 8
> >
> > This should refetch the value from the target.  What value
> is cached?
>
> This value didn't really changed. It just be changed in cache, but
> not memory. If you s or rs and check "a" again, you will found that
> "a"'s value is right.

I think Hui is right. I ran another test with printf and stopping precord
and the memory seems ok, please see session below.

> BTW, this is really a strange thing. If answer is enter, everything
> is OK. If answer is no, it was changed.

For me the problem happens both times, when pressing 'n' or <enter>.
(you can see that in the session below too)

(gdb) l
1 #include <stdio.h>
2 int main()
3 {
4 int a = 0;
5 printf("a is %d\n",a);
6 return 0;
7 }
(gdb) start
Temporary breakpoint 1 at 0x8048485: file a.cc, line 4.
Starting program: /local/lmckhou/testing/a.out
re
Temporary breakpoint 1, main () at a.cc:4
4 int a = 0;
(gdb) rec
(gdb) n
5 printf("a is %d\n",a);
(gdb) n
a is 0
6 return 0;
(gdb) rn
5 printf("a is %d\n",a);
(gdb) p a
$1 = 0
(gdb) set var a=8
Because GDB is in replay mode, writing to memory will make the execution log unusable from this point onward. Write memory at address 0xbfffadf0?(y or [n])
Process record canceled the operation.
(gdb) p a
$2 = 8
(gdb) rec stop
Delete recorded log and stop recording?(y or n) y
(gdb) p a
$3 = 8
(gdb) n
a is 0 <------------------------------------------ a is actually set correctly
6 return 0;
(gdb) p a
$4 = 0

>
>
> >
> >> 2009-09-14  Hui Zhu  <teawater@gmail.com>
> >>
> >>       * record.c (record_xfer_partial): Call free_all_values when
> >>       cancel the operation.
> >
> > I don't think this is a good idea; this is a memory management
> > function.  It's not supposed to change the apparent values.
> >
>
> Agree. Looks we have a strange thing need to be handled.
>
>
> Thanks,
> Hui
>