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Debugging classes.
- From: John Coppens <john at jcoppens dot com>
- To: gdb at sourceware dot org
- Date: Fri, 1 Oct 2010 15:07:05 -0300
- Subject: Debugging classes.
Hello people.
I'm getting the following error message in places I wouldn't expect it.
I don't know if this is a gdb bug (I've seen some messages about similar
problems), or a programming error of mine:
Cannot access memory at address 0xb7
Gdb version is 7.1, distro is Slackware 13.1 (updated).
This is the sequence of events leading to the error:
1) in a main program, I declared an instance of class SingleStep:
SingleStep stepper;
2) I set a breakpoint inside method ::step, start the program, and
get to the breakpoint:
Breakpoint 1, SingleStep::step (this=0x6067e0, mem=0x607030,
pc=0x7fffffffdcdc) at step.cpp:670 670 switch (opcode[opc_line].operation) {
(gdb) p this
$1 = (SingleStep * const) 0x6067e0
(All as expected)
3) After a few loops ('this' is still the same), I enter into a call from the
same class:
689 case OP_JGE: do_jump_if(mem, pc, opc, !(get_SR_bit(SR_N) ^ get_SR_bit(SR_V))); break;
(gdb) s
SingleStep::get_SR_bit (this=0x6067e0, mem=0x607030, pc=0x7fffffffdcdc) at step.cpp:716
716 return (r[REG_SR] & (1 << bit)) != 0;
(gdb) p this
$2 = (SingleStep * const) 0xf
Why is SingleStep suddenly 0xf? Of course, I can't access internal variables
with this value:
(gdb) p r
Cannot access memory at address 0x67
(gdb) p this->r
Cannot access memory at address 0x67
I'd appreciate suggestions here!
John
BTW: the get_SR_bit method called is:
int
SingleStep::get_SR_bit(int bit)
{
return (r[REG_SR] & (1 << bit)) != 0;
}
It is declared as a private method of SingleStep.