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ptrace behavior accessing ar.lc and ar.ec

Linux-ia64 Weihaw Chuang 2 participants 3 messages Jan 25, 2002

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Weihaw Chuang

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#0 lore raw

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
[email protected]

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

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#1 lore raw
Quoted 9 lines

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.

Quoted 7 lines

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

The tracing program observes some sort of behavior like:

Quoted 8 lines

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
#2 lore raw
In reply to Weihaw Chuang

Hi Wei,

Quoted 1 line
Quoted 1 line
Quoted 1 line
Quoted 1 line
Quoted 1 line · On Fri, 25 Jan 2002 08:43:28 -0800 (PST), [email protected] 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