Re: [RFA] Repost ARM frame patches

[Andrew Cagney <ac131313@redhat.com>]

>> i.e. GCC emits _empty_ dwarf unwind information for thumb functions,
>> rather than none at all.  That's unlikely to work.  We'd need to modify
>> the dwarf2 unwinder to ignore empty FDEs.
>> 
>> I'll check in the non-dwarf parts now, and then we can figure out what
>> to do about that.
> 
> 
> Though of course a trivial leaf function *will* have an empty FDE.  
> Consider
> 
> int func(void) { return 0;}
> 
> Which compiles to 
> 
> 	mov	r0, #0
> 	bx	lr
> 
> I would have thought that wouldn't need any frame unwind information.  So 
> we would have a problem distinguishing trivial cases from "not generated" 
> cases.

FYI, the dwarf2 spec (draft 7) doesn't specify the disposition of 
unspecified registers that result from an empty or under populated CFI 
info - such registers are truly undefined.  GCC is pushing the bounds of 
well defined behavior in emitting such info.

Andrew