On Fri, Aug 17, 2012 at 08:06:07AM +0100, Arnd Bergmann wrote:

Sorry for the dumb question, but why do you even need PTRACE_GET_THREAD_AREA
for 64 bit tasks? I thought the thread pointer is a GPR, or is this just
for compat tasks?

The TLS is stored in a co-processor register which is read-only for
userspace. However, it's banked, so accessing the TLS of your child (the guy
you're ptracing) requires a system call.

Will