Re: observe & control thread state for exit futex ?

[John Reiser]

Daniel Jacobowitz wrote:
> On Sun, Apr 13, 2003 at 07:52:08PM -0700, John Reiser wrote:
> 
>>How can a debugger, newly attached to an arbitrary thread, determine whether
>>the thread has a pending exit futex and associated memory location to clear
>>[CLONE_CHILD_CLEARTID flag and child_tid_ptr parameter at __clone()]?
>>
>>If so, then how can the debugger determine the address, change the address,
>>cancel the futex, and/or intercept the notification?
> 
> 
> It can't.  Even clone flags are not accessible.
> 
> If you can think of a good reason that a debugger would need any
> particular piece of data, exposing it is very straightforward.
> 

The debugger needs this information to determine the state of the thread.
An automated software audit program needs the information to verify
that threads are working correctly.  In general, write-only state
[from the viewpoint of the thread] is a bad idea.

Would a new option to sys_prctl() be a good way to expose the data?