[Linux-ia64] ptrace behavior accessing ar.lc and ar.ec

Hi folks,
I'm using the ptrace interface to create a
"architectural" processor state tracing tool.  When I
access AR.LC and AR.EC, I *usually* get the expected
result, but every once and a while it returns a bogus
result.

Is there a known bug, or am I using ptrace
incorrectly?

Here's how its used:
lc = ptrace (PTRACE_PEEKUSER, state->pid, PT_AR_LC,
0);

The tracing program observes some sort of behavior
like:

mov.i ar.lc = r61    (I'm pretty sure r61 is 6), and  
                       ptrace returns 0 
sxt4  r22=r60        ptrace returns -1
.....                "
(swp kernel code)    "
.....                "
br.ctop.sptk.few .b9 ptrace returns -1, br taken 
(p17) st8 [r15]=r34  ptrace returns 5

Many thanks,
-Wei


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Weihaw Chuang
wchuang@cs.ucsd.edu

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