Re: [PATCH] ptrace: add ability to get clear_tid_address

[Pedro Alves <palves@redhat.com>]

On 02/08/2012 05:31 PM, Oleg Nesterov wrote:
> On 02/08, Pedro Alves wrote:
>>
>> I just tried it.  This is &pthread->tid in glibc/libpthread, so with debug
>> info it's easy to figure out where to set the watchpoint manually with gdb
>> without asking the kernel.  Doesn't work.  ptrace doesn't show any trap
>> for the kernel writes.
> 
> The tracee simply can't report this trap. it is already dead ;) and
> hw breakpoint (used by ptrace) is "pinned" to the thread.

Right, as I said.  :-)  I saw that a watchpoint trap isn't reported either
for the CLONE_CHILD_SETTID case (that is, within clone, when the kernel
writes the tid to the memory address passed in to the clone syscall).
I wouldn't have been surprised to see the trap in userspace in either
the parent or the child, though I'm not really surprised to not
see it either.

-- 
Pedro Alves