Hardware breakpoint on C++ reference modification in gdb - c++

Question

C++ standard says that it is unspecified whether or not a reference requires storage (3.7).. However, as far as I understand, gcc implements C++ references as pointers and as such they can be corrupted.
Is it possible to get an address of a reference in gdb and put a hardware breakpoint on that address in order to find out what corrupts the memory where the reference resides? How can one set such a breakpoint?

Answer 1

GDB may does hardware watchpointing. You can use command watch for this. Example:
main.cpp:
int main(int argc, char **argv)
{
int a = 0;
int& b = a;
int* c = &a;
*c = 1;
return 0;
}
Start debugging and set breakpoint on start main function and end main function:
(gdb) b main
Breakpoint 1 at 0x401bc8: file /../main.cpp, line 60.
(gdb) b main.cpp:65
Breakpoint 2 at 0x401be9: file /../main.cpp, line 65.
(gdb) r
Get address of reference b:
Breakpoint 1, main (argc=1, argv=0x7fffffffddd8) at /../main.cpp:60
60 int a = 0;
(gdb) disas /m
Dump of assembler code for function main(int, char**):
59 {
... Something code
60 int a = 0;
=> 0x0000000000401bc8 <+11>: movl $0x0,-0x14(%rbp)
61 int& b = a;
0x0000000000401bcf <+18>: lea -0x14(%rbp),%rax
0x0000000000401bd3 <+22>: mov %rax,-0x10(%rbp)
62 int* c = &a;
0x0000000000401bd7 <+26>: lea -0x14(%rbp),%rax
0x0000000000401bdb <+30>: mov %rax,-0x8(%rbp)
63 *c = 1;
0x0000000000401bdf <+34>: mov -0x8(%rbp),%rax
0x0000000000401be3 <+38>: movl $0x1,(%rax)
64
65 return 0;
0x0000000000401be9 <+44>: mov $0x0,%eax
66 }
0x0000000000401bee <+49>: pop %rbp
0x0000000000401bef <+50>: retq
End of assembler dump.
(gdb) p $rbp-0x10
$1 = (void *) 0x7fffffffdce0
p $rbp-0x10 is printing address of reference b. It is 0x7fffffffdce0.
Set this address for watching:
(gdb) watch *0x7fffffffdce0
Hardware watchpoint 3: *0x7fffffffdce0
(gdb) c
GDB break only if value is changed:
(gdb) c
Continuing.
Hardware watchpoint 3: *0x7fffffffdce0
Old value = -8752
New value = -8996
main (argc=1, argv=0x7fffffffddd8) at /../main.cpp:62
62 int* c = &a;
Sorry for my english!