c++ - Setting GDB hardware watchpoint/how to set software watchpoint

Question

An earlier question explained that on x86 the size of objects being watched is limited by debug registers. As expected, I can "watch" a double variable. But I can't watch a double datamember, for example,

watch pObject->dPrice

produces

Hardware watchpoint 1: pObject->dPrice

But when you try to continue execution, it says

Could not insert hardware breakpoints: You may have requested too many hardware breakpoints/watchpoints.

even though this is the only breakpoint/watchpoint.

I'm curious why this is so, but more importantly is there a way around it? According to GDB documentation it may use software watchpoints if it can't use hardware. In this case it makes no attempt to use a software watchpoint -- is there a way to force it to do so?

Answer 1

Yes, you can:

set can-use-hw-watchpoints 0

From 5.1.2 Setting Watchpoints:

You can force GDB to use only software watchpoints with the set can-use-hw-watchpoints 0 command. With this variable set to zero, GDB will never try to use hardware watchpoints, even if the underlying system supports them. (Note that hardware-assisted watchpoints that were set before setting can-use-hw-watchpoints to zero will still use the hardware mechanism of watching expression values.)

set can-use-hw-watchpoints

    Set whether or not to use hardware watchpoints.

show can-use-hw-watchpoints

    Show the current mode of using hardware watchpoints.