Messages in this thread | | | Date | Mon, 26 Feb 2007 15:51:54 -0800 | From | Stephane Eranian <> | Subject | debug registers and fork |
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Hello,
I have come across an issue with a monitoring using the hardware debug registers on ia64/i386/x86-64.
It seems that the way debug registers are inherited across fork differs between ia-64 and i386/x86-64. On ia-64, the debug registers are NEVER inherited in the child. The copy_thread() routine clears the necessary thread flags to avoid reloading the debug registers in the child.
Now, on x86-64, it appears that the TIF_DEBUG flag is inherited via setup_thread_stack(). By virtue of dup_task_struct() the debug registers get copied into the child task on fork. So the child has active breakpoints, unless I am mistaken somewhere.
Given the way the ptrace() interface works, I would tend to think that the ia-64 way is the correct one. Any comment?
Furthermore, on i386/x86-64, when switching out from a task with TIF_DEBUG enabled to another which does not, it seems we do not clear the debug registers (at least dr7) so they become inactive.
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