utrace plans

[stephane eranian]

Roland,

On Wed, May 14, 2008 at 6:29 AM, Roland McGrath <roland at redhat.com> wrote:
>
>  What I have right now is a version where utrace is enabled alongside
>  the old ptrace implementation.  The hooks into core code are cleaned
>  up via tracehook.h, but ptrace still works the same old way.  With
>  this, they both work, but they don't play well together on the same
>  thread (one doesn't understand when the other is stopped, etc).  After
>  getting the revamped utrace interface on its feet, the next job will
>  be to find an uncomplicated way to make ptrace use utrace (or
>  cooperate well with utrace) for its thread stops.
>
That will be a problem for perfmon applications. Existing applications use
ptrace() to stop/resume another thread. My current utrace experiment relies
on the fact that you can attach a utrace engine and actually quiesce the thread
even though it is already stopped by ptrace. And conversely when you want to
resume. From the above, I get a feeling this won't work at least initially.