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


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