PATCH/RFC handle missing DW_AT_comp_dir attribute

[Richard Earnshaw]

> 
> Richard Earnshaw <rearnsha@arm.com> writes:
> > This problem was found by a colleague while using GDB with the ADS tools.
> > 
> > These tools do not set the DW_AT_comp_dir attribute in a compilation unit 
> > entry, so GDB will crash trying to reference a NULL pointer.

> 
> Sorry --- how does this patch fix a GDB crash?  GDB doesn't use BFD to
> read debugging information.

Ah, sorry, it was my understanding from Ian that it was in GDB.  
Apparently the problem was seen in addr2line, and rather than a crash we 
just got an empty filename (since the first argument passed to concat was 
a NULL pointer).

R.