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

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

[Weihaw Chuang]

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


==************************************************************

Weihaw Chuang
wchuang@cs.ucsd.edu

************************************************************

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

[David Mosberger]

 > 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?

Not a known bug.

 > 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

Do you have a self-contained and small test program that reproduces
the problem?  That would make it easier to investigate the problem.

	--david

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

[David Mosberger]

Hi Wei,

>>>>> On Fri, 25 Jan 2002 08:43:28 -0800 (PST), wei@baldursgate.ucsd.edu said:

  Wei> Hi David, Thanks for replying.  Here's a reduced testcase that
  Wei> replicates the result.  Its derived from the utrace.c program
  Wei> you gave me a long time ago.

I can't reproduce the problem with 2.4.17.

  Wei> I'm currently using "Linux version 2.4.3-12smp" "Red Hat Linux
  Wei> 7.1 2.96-85".

That's a very old kernel.  Can you try after upgrading to something
more recent?

Thanks,

	--david