Re: looking for help interpreting softlockup/stack trace

[David Daney <ddaney@avtrex.com>]

Ralf Baechle wrote:
> On Wed, Aug 06, 2008 at 11:57:32AM -0700, David Daney wrote:
> 
>>>> In the trace below, is "epc" the program counter at the time of the   
>>>> timer interrupt?  How does "ra" fit into this, given that the 
>>>> function  whose address it contains isn't seen in the stack trace 
>>>> until quite a  ways down?
>>> $LBB378 is an internal symbol.  The value of RA may not be very informative
>>> if it was overwritten by a random subroutine call.
>>>
>> I have thought about eliminating these internal labels when the module's symbols are read.  Would this make any sense?
> 
> I think so.  Maybe that could even be done when the module is linked.  I
> don't think there are ever any relocations against these local symbols.
> Thiemo?
> 

I take it back.  Most of the $LC... symbols (typically string constants) are needed for relocations.  Currently I cannot find in my builds any $LB... symbols.  I wonder if gcc-4.3 eliminates these.

I think the reason they show up in stack traces is that they are data pointers that have been stored on the stack that are misinterpreted as function return addresses.


I wonder what would happen if we compiled all the code with -funwind-tables and had a small DWARF2 unwinder ala GCC's C++ exception handling mechanism.  That would allow exact stack traces with no runtime overhead.  

David Daney