Print Stacktrace on Runtime Error

Print Stacktrace on Runtime Error

[Alexander Lochmann]

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Hi folks!

My stap scripts keeps failing either with  a "user string copy fault" or
with a "read fault".
Is there a way get more context information about the error? A
stacktrace for example? :)

Thanks!

Cheers,
Alex

-- 
Technische Universität Dortmund
Alexander Lochmann                PGP key: 0xBC3EF6FD
Otto-Hahn-Str. 16                 phone:  +49.231.7556141
D-44227 Dortmund                  fax:    +49.231.7556116
http://ess.cs.tu-dortmund.de/Staff/al


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Re: Print Stacktrace on Runtime Error

[William Cohen]

On 07/14/2016 01:19 PM, Alexander Lochmann wrote:
> Hi folks!
> 
> My stap scripts keeps failing either with  a "user string copy fault" or
> with a "read fault".
> Is there a way get more context information about the error? A
> stacktrace for example? :)
> 
> Thanks!
> 
> Cheers,
> Alex
> 

Hi Alex,

Is this script using the user_string function?  Is the script actually passing in a valid pointer?  It might be useful to print out the value being passed to user_string to see if it valid and makes sense. Could you post the script that is causing the problem?

-Will

Re: Print Stacktrace on Runtime Error

[Josh Stone]

On 07/14/2016 10:41 AM, William Cohen wrote:
> On 07/14/2016 01:19 PM, Alexander Lochmann wrote:
>> Hi folks!
>> 
>> My stap scripts keeps failing either with  a "user string copy
>> fault" or with a "read fault". Is there a way get more context
>> information about the error? A stacktrace for example? :)
>> 
>> Thanks!
>> 
>> Cheers, Alex
>> 
> 
> Hi Alex,
> 
> Is this script using the user_string function?  Is the script
> actually passing in a valid pointer?  It might be useful to print out
> the value being passed to user_string to see if it valid and makes
> sense. Could you post the script that is causing the problem?

It's also possible that a user pointer is perfectly valid, just not
paged in.  Since stap handlers run in atomic context, we can't take a
page fault to populate that memory.

Stap's try-catch mechanism might be helpful to you, whether to continue
past any encountered faults, or print your diagnostics like a backtrace.