Subj : suspend a kernel thread in AIX and get register contents
To   : comp.unix.aix,comp.programming.threads
From : kamalp
Date : Wed Mar 23 2005 06:45 am

Hello,

 I am using AIX 5.3. The /proc filesystem contains an lwpstatus -which
holds the registers of the currently executing thread. Unfortunately,
the registers can only be accessed when the thread is suspended. So
the problem is like this:-
 user_process -> syscall ->kernel extension code ->get_registers()

I want to spawn a new kernel thread and block for this thread, while
the other thread gets the registers for this thread. But I am running
into a problem.

int my_func(void* data)
{
 open /proc/lwp/<thid>/lwpstatus & read register contents.
 e_wakeup_thread(&event);
 e_clear_wait(<thid>, THREAD_TIMED_OUT); /* just in case it wasn't
awakened */
}
my_kern_code () 
{
 int *event;

 tid = thread_create();
 kthread_start(tid, my_func, (void*)(event+thread_self), datasize,
NULL, NULL);
 e_sleep_thread(&event, NULL, NULL);
}
----------------------

This code doesn't seem to work. It actually hangs the whole kernel as
if it got stuck in a deadlock. Also, one piece of aix documentation
says thread_create can be used in process context. Another says it has
to be used in kernel process only and not in an extension. Why this
contradiction/restriction?
Further, is there any syscall that can be called from kernel extension
to get register contents? Why wouldn't ptracex() or its equivalent
code be made available to kernel extensions?

thanks
-kamal

.