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Re: trace_printk() support in trace-cmd

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On 12/13/2010 01:20 PM, Masami Hiramatsu wrote:
(2010/12/13 2:47), Avi Kivity wrote:
>  On 12/12/2010 07:43 PM, Arnaldo Carvalho de Melo wrote:
>>  Em Sun, Dec 12, 2010 at 07:42:06PM +0200, Avi Kivity escreveu:
>>  >   On 12/12/2010 07:36 PM, Arnaldo Carvalho de Melo wrote:
>>  >   >Em Sun, Dec 12, 2010 at 06:35:24PM +0200, Avi Kivity escreveu:
>>  >   >>    On 11/23/2010 05:45 PM, Steven Rostedt wrote:
>>  >   >>    >Again, the work around is to replace your trace_printks() with
>>  >   >>    >__trace_printk(_THIS_IP_, ...) or just modify the trace_printk() macro
>>  >   >>    >in include/linux/kernel.h to always use the __trace_printk() version.
>>  >   >>
>>  >   >>    This works; I'm using it for now (I tried to use 'perf probe', but I
>>  >   >>    get unpredictable results, like null pointer derefs).
>>  >   >
>>  >   >Can you tell us which functions, environment, etc?
>>  >
>>  >   Something around 2.6.27-rc4; example functions are FNAME(fetch) in
>>  >   arch/x86/kvm/paging_tmpl.h; compiled modular (which was Steven's
>>  >   guess as to why it fails).
>>  >
>>  >   (note, the failure is with trace-cmd, not /sys/kernel/debug/tracing).
>>
>>  I mean the "I tried to use 'perf probe'" part.
>
>  Well, same, more or less.
>
>    perf probe -m kvm --add 'fetch_access=paging64_fetch pt_access=gw->pt_access pte_access=gw->pte_access dirty'
>
>  would return garbage for gw->*, and the log would show the exception handler called.  gw is most certainly valid.
>

Thank you for reporting.
Hmm, actually, pagefaults could happen on fetching variables. But
fetching argument routines should handle it...

They did handle it (or so I understood from the logs). But they shouldn't have occured in the first place, since gw was dereferenceable (and the function dereferences it). So something went wrong while fetching gw itself (do you interpret the dwarf tables to find where the variable is stored?)

I'd like to check it, could you tell me details? for example, that exception log,
kprobe-tracer's event definition(you can see it via debugfs/tracing/kprobe-events)
and the result of `perf probe -L paging64_fetch:0-10`.

I no longer have the logs, I'll try to reproduce it later.

--
error compiling committee.c: too many arguments to function

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