Debug registers on FreeBSD

[Kostik Belousov]

On Thu, Feb 18, 2010 at 09:44:24AM -0500, John Baldwin wrote:
> On Wednesday 17 February 2010 11:07:36 pm Anderson Eduardo wrote:
> > 
> > Hello Folks,
> > 
> > First, I'm starting in the world of the debugging FreeBSD Kernel and, I 
> don't know to use kgdb and ddb properly and, I need set breakpoints using 
> debug register. Those breakpoints in the all tasks.
> 
> This last might be tricky to accomplish because cpu_switch() will swap out
> the debug registers if a thread is using them.  However, you can easily
> manage hardware breakpoints from ddb using the 'hwatch' command.  It is 
> documented in ddb(4).  kgdb doesn't support setting hardware watch points
> it seems.  Note that you can try to use 'db_md_set_watchpoint()' from your
> kernel module (with DDB compiled into your kernel) if you want to set the
> address progammatically rather than via the 'hwatch' command in ddb.

I remember that ddb only sets %dr on the CPU it happens to execute.
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