Can kernel.statement access the function argument?

Can kernel.statement access the function argument?

[voyager1983]

Hi, All

I am trying to access the argument of kernel function in kernel.statement
probe point. But I get the error message:

semantic error: not accessible at this address (0xc01a82e0): identifier
'$irq' at question.stp:2:38
        source:         printf("irq number is %d\n", $irq)
                                                     ^
Pass 2: analysis failed.  Try again with another '--vp 01' option.

The question.stp file is as below:

probe kernel.statement("handle_IRQ_event@kernel/irq/handle.c:376"){
        printf("irq number is %d\n", $irq)
}

I am using SystemTap 1.3 on Ubuntu10.10 to trace the kernel 2.6.35.9.

Are we allowed to access the function argument in kernel.statement probe
point? If not, is there any walk around solution?

Thanks!
Joey



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Re: Can kernel.statement access the function argument?

[William Cohen]

On 04/07/2011 11:52 PM, voyager1983 wrote:
> 
> Hi, All
> 
> I am trying to access the argument of kernel function in kernel.statement
> probe point. But I get the error message:
> 
> semantic error: not accessible at this address (0xc01a82e0): identifier
> '$irq' at question.stp:2:38
>         source:         printf("irq number is %d\n", $irq)
>                                                      ^
> Pass 2: analysis failed.  Try again with another '--vp 01' option.
> 
> The question.stp file is as below:
> 
> probe kernel.statement("handle_IRQ_event@kernel/irq/handle.c:376"){
>         printf("irq number is %d\n", $irq)
> }
> 
> I am using SystemTap 1.3 on Ubuntu10.10 to trace the kernel 2.6.35.9.
> 
> Are we allowed to access the function argument in kernel.statement probe
> point? If not, is there any walk around solution?
> 
> Thanks!
> Joey
> 
> 
> 

Hi Joey,

SystemTap's ability to obtain target variables depends on whether the argument is available at that location and whether the compiler has include debuginfo that describe where to get the value. To see what target variables systemtap can find at that location you could do:
 
stap -L 'kernel.statement("handle_IRQ_event@kernel/irq/handle.c:376")'

Is the place you probing the same as like 376 in:

http://lxr.linux.no/#linux+v2.6.35.9/kernel/irq/handle.c#L376

Could you use the following probe point?

kernel.trace("irq_handler_exit") $irq:int $action:struct irqaction* $ret:int

-Will

Re: Can kernel.statement access the function argument?

[voyager1983]

Hi, William

What I am about to probe is actually the statement   

ret = action->handler(irq, action->dev_id);

located in 

http://lxr.linux.no/linux+v2.6.35.9/kernel/irq/handle.c#L375

I want to selective do the probe according to the value of argument irq
(such as only probe interrupt issued by the keyboard).
 
kernel.trace("irq_handler_exit") works for me. But how can I do in some
other functions if the tracing line doesn't surrounded by the function like 
trace_irq_handler_entry and trace_irq_handler_exit. 

BTW, when I execute the command

stap -L 'kernel.statement("handle_IRQ_event@kernel/irq/handle.c:376")'

It returns nothing.

Best regards,
Joey




William Cohen wrote:
> 
> On 04/07/2011 11:52 PM, voyager1983 wrote:
>> 
>> Hi, All
>> 
>> I am trying to access the argument of kernel function in kernel.statement
>> probe point. But I get the error message:
>> 
>> semantic error: not accessible at this address (0xc01a82e0): identifier
>> '$irq' at question.stp:2:38
>>         source:         printf("irq number is %d\n", $irq)
>>                                                      ^
>> Pass 2: analysis failed.  Try again with another '--vp 01' option.
>> 
>> The question.stp file is as below:
>> 
>> probe kernel.statement("handle_IRQ_event@kernel/irq/handle.c:376"){
>>         printf("irq number is %d\n", $irq)
>> }
>> 
>> I am using SystemTap 1.3 on Ubuntu10.10 to trace the kernel 2.6.35.9.
>> 
>> Are we allowed to access the function argument in kernel.statement probe
>> point? If not, is there any walk around solution?
>> 
>> Thanks!
>> Joey
>> 
>> 
>> 
> 
> Hi Joey,
> 
> SystemTap's ability to obtain target variables depends on whether the
> argument is available at that location and whether the compiler has
> include debuginfo that describe where to get the value. To see what target
> variables systemtap can find at that location you could do:
>  
> stap -L 'kernel.statement("handle_IRQ_event@kernel/irq/handle.c:376")'
> 
> Is the place you probing the same as like 376 in:
> 
> http://lxr.linux.no/#linux+v2.6.35.9/kernel/irq/handle.c#L376
> 
> Could you use the following probe point?
> 
> kernel.trace("irq_handler_exit") $irq:int $action:struct irqaction*
> $ret:int
> 
> -Will
> 
> 

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Re: Can kernel.statement access the function argument?

[Frank Ch. Eigler]

voyager1983 <wang.yongzhi2009@gmail.com> writes:

> What I am about to probe is actually the statement   
> ret = action->handler(irq, action->dev_id);
> [...]
> stap -L 'kernel.statement("handle_IRQ_event@kernel/irq/handle.c:376")'
> It returns nothing.

That's partly because the handle_IRQ_event function is blacklisted due
to some historical incompatibility with kernel kprobes.  You may try
again with stap -g ...

- FChE

Re: Can kernel.statement access the function argument?

[voyager1983]

I see. Many thanks!

Joey

Frank Ch. Eigler wrote:
> 
> voyager1983 <wang.yongzhi2009@gmail.com> writes:
> 
>> What I am about to probe is actually the statement   
>> ret = action->handler(irq, action->dev_id);
>> [...]
>> stap -L 'kernel.statement("handle_IRQ_event@kernel/irq/handle.c:376")'
>> It returns nothing.
> 
> That's partly because the handle_IRQ_event function is blacklisted due
> to some historical incompatibility with kernel kprobes.  You may try
> again with stap -g ...
> 
> - FChE
> 
> 

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