RE: Auto-deleting watchpoints

[Mihai Basa <Mihai dot Basa at NUIGALWAY dot IE>]

>===== Original Message From Eli Zaretskii <eliz@elta.co.il> =====
>> Date: Tue, 2 Dec 2003 15:44:51 -0500
>> From: Daniel Jacobowitz <drow@mvista.com>
>> >
>> > This includes deleting local watchpoints even when the program makes a 
call to
>> > a library function (say, sqrt()). I believe this auto-deletion _severly_
>> > reduces the practicality of watchpoints, because they simply go away on 
the
>> > first call they hit!
>>
>> That is not what is supposed to happen.  The watchpoint should stay
>> until the function containing the local variable has exited.
>
>Right.  And I have simple test cases to prove it.
>
>Mihai, you probably discovered a bug.  Please send a test case.


I've tried this with gdb-6.0, and the fenomenon seems to have disappeared, but 
I've only tested it lightly. I didn't really manage to isolate the bug, as it 
only appeared in certain configurations of the source code, and showed up in 
different places (so the test case is not simple at all). It appears that 
gdb-6.0 has somehow solved this.

To summarize what was happening in gdb-5.3:
 A watchpoint is set on an element of a malloc'ed array. The pointer to this 
array is sent to a subroutine, where, after a while, the previously-set watch 
gets deleted on a call to printf. The message produced is:

        Watchpoint 2 deleted because the program has left the block in
        which its expression is valid.
        0x4008e00e in vfprintf () from /lib/i686/libc.so.6

and the source-line on which the watchpoint to "active_id[123]" got deleted 
is:

        printf("from i = %i at %lf  at vel= %lf ", i,P[i].x[0] ,P[i].u[0]);

(it has nothing to do with active_id[123]). The backtrace was:
        (gdb) backtrace
        #0  0x4008e00e in vfprintf () from /lib/i686/libc.so.6
        #1  0x00000000 in ?? ()


Now gdb-6.0 displays the 'watchpoint deleted' message only when it hits the 
end of the program (in a library function called "_fini()").


Regards,
Mihai Basa