Consider PowerPC and the $ps register (MSR). When debugging a kernel or
embedded application, GDB has pretty complete control (?) over this
register. In GNU/Linux userspace, however, only two bits of it can be set.
The rest are read-only.
So what happens if you "set $ps = 0"? Well, the right thing happens, but
until the next time the target stops "print $ps" will print 0. Which is not
actually the value of the $ps register.
Here's the options that I see:
- Ignore and document this.
- Refetch registers after storing them.
- Invalidate registers for lazy re-fetch after storing them.
- Add a target hook for might-be-volatile registers, and invalidate
only those registers after storing them - or don't cache them at
all.
Thoughts? Is this a problem worth fixing?