Re: [PATCH/i386newframe/RFC] DWARF CFI frame unwinder

[Andrew Cagney <ac131313@redhat.com>]

>> >The frame's CFA is the basis for identifying the frame and locating
>> >saved registers in the CFI.  It is always present when you have CFI.
>> >
>> >DW_AT_frame_base is the basis for locating saved variables and locals. 
>> >It is generally present when you have DWARF-2 debug info.
> 
>> 
>> You and I went through all this not too long ago.  frame-base is for 
>> this high level thingie, frame-unwind is for the low level register 
>> information.
> 
> 
> Then, as Mark said, it shouldn't be providing a frame base at all.  The
> CFA information is not the right frame base, and the use of
> DW_AT_frame_base is exactly orthogonal to the use of CFI.

Daniel, you and I went through all this not too long ago.

Not providing a dwarf2 specific frame-base (returning DW_AT_frame_base) 
leads to ``info frame'' printing inconsistent information.  It will 
report ``id.stack_addr'' as the frame's base and that is definitly not 
correct - it won't match the high level ``base'' that the user expects 
to match a disassembler.

Again, this is why the high level frame-base is separate to the low 
level frame-unwind.  It is possible to mix 'n' match.

However, it doesn't need to be implemented right now - at present 
dwarf2loc short circutes frame-base, implementing DW_AT_frame_base locally.

Andrew