Re: Backward compatibility for insn probe point

[David Smith <dsmith@redhat.com>]

Roland McGrath wrote:
>> Off the top of my head that might mean there is a specific ppc64 utrace
>> problem.
>>
>> Roland, do you know of any problems with original utrace doing
>> UTRACE_ACTION_SINGLESTEP on ppc64?
> 
> Sorry, I can't remember anything in particular.  There might well have been
> some issue that I've forgotten.

I've done some more debugging here, and I thought I'd let you know what
I've found.  The problem occurs on all versions of 2.6.25 I've found
(which uses the original utrace).  On the earliest version of 2.6.26
I've found (2.6.26.3-17.fc9.ppc64) which uses the new utrace, this works
correctly.

Digging a bit deeper into the behavior on failing kernels, I've found
that if you set up an insn probe point and a syscall probe, you get only
one insn probe hit before each syscall.  Note that gdb is fully able to
do instruction stepping on failing kernels, so ptrace seems to be
working correctly.

-- 
David Smith
dsmith@redhat.com
Red Hat
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