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Invalid program counters and unwinding

Michael Matz matz@suse.de
Mon Jul 2 15:48:00 GMT 2018 
Hi,

On Thu, 28 Jun 2018, Jeff Law wrote:

> I believe "dumb" is referring to the fact that we're already in a bit of 
> a weird state as evidenced by the NULL FDE.  Blindly trying to read the 
> contents of the PC that we couldn't map to an FDE is, IMHO, dumb.
> 
> One might even be able to argue in this day and age that we should have 
> suitable descriptors for everything.  If no suitable descriptor is found 
> then backtracing should stop.  Lack of suitable descriptors in any code 
> would be considered a bug in that scenario.

I disagree.  ASM code often lacks unwind descriptors (now less than in the 
past, but still).  My rule of thumb is always: no descriptor -> has to be 
a framepointer-using routine with standard calling sequence.  (I.e. 
declare the combination of no descriptor and no fp to be a bug).  Some of 
the callee-saved register will temporarily be wrong but unwinding can 
continue.


Ciao,
Michael.
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