Re: ptrace in 2.6.5

From: Andi Kleen
Date: Mon May 10 2004 - 13:51:19 EST

Fabiano Ramos <ramos_fabiano@xxxxxxxxxxxx> writes:

> Hi All.
> Is ptrace(), in singlestep mode, required to stop after a int 0x80?
> When tracing a sequence like
> mov ...
> int 0x80
> mov ....
> ptrace would notify the tracer after the two movs, but not after the
> int 0x80. I want to know if it is a bug or the expected behaviour.

What happens is that after the int 0x80 the CPU is in ring 0 (you
don't get an trace event in that mode unless you use a kernel debugger).
Then when the kernel returns the last instruction executed before it is an
IRET. But the IRET is also executed still in ring 0 and you should not get
an event for it (you can not even access its code from user space).

So it's expected behaviour.


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