Re: how to continue from a breakpoint in GNU/Hurd

[Richard Braun <rbraun@sceen.net>]

On Thu, Jul 18, 2013 at 12:22:07AM +0800, Yue Lu wrote:
> On Thu, Jul 18, 2013 at 12:13 AM, Richard Braun <rbraun@sceen.net> wrote:
> > On Thu, Jul 18, 2013 at 12:07:20AM +0800, Yue Lu wrote:
> >> when I used thread_info() to check the suspend count, they are zero.
> >> But I met a strange thing.
> >> this is my code snippet:
> >> thread_basic_info_data_t _info;
> >> thread_basic_info_t info = &_info;
> >> mach_msg_type_number_t info_len = THREAD_BASIC_INFO_COUNT;
> >> error_t err =
> >>   thread_info (thread->port, THREAD_BASIC_INFO, (int *) &info, &info_len);
> >>
> >> after this call, the info turn out to be a  _NULL_ pointer. I think
> >
> > If the info pointer is NULL, how do you determine the suspend count ?
> >
> I used this (&_info)->suspend_count to get the sc value.
> 
> > Something does look wrong. Check all the parameters of your call, one
> > by one, rigorously.
> 
> The only one parameter I used is the first one, I give it as the
> thread port, something like 119 (I have printf it), the left three
> parameters are all the same as the code in gnu-nat.c.

So, in the end, the code (which is taken from GDB) is wrong. It uses
&info, the address of a pointer to _info, where it should use &_info or
info instead. The kernel happily writes the thread info there, erasing
the pointer on the way.

-- 
Richard Braun