GDB hardware watchpoint very slow - why?
- by Laurynas Biveinis
On a large C application, I have set a hardware watchpoint on a memory address as follows:
(gdb) watch *((int*)0x12F5D58)
Hardware watchpoint 3: *((int*)0x12F5D58)
As you can see, it's a hardware watchpoint, not software, which would explain the slowness.
Now the application running time under debugger has changed from less than ten seconds to one hour and counting. The watchpoint has triggered three times so far, the first time after 15 minutes when the memory page containing the address was made readable by sbrk. Surely during those 15 minutes the watchpoint should have been efficient since the memory page was inaccessible? And that still does not explain, why it's so slow afterwards.
The GDB is
$ gdb --version
GNU gdb (GDB) 7.0-ubuntu
[...]
Thanks in advance for any ideas as what might be the cause or how to fix/work around it.
