[Dwarf-Discuss] Segment selectors for the range list table.

[Michael Eager]

> Perhaps it's more like Paul was postulating - that the spec assumes code 
> is in a code segment/doesn't need to be clarified. (but that gets a bit 
> confused in debug_aranges - if it only is meant to contain code (not 
> data), why does it need a segment selector - and also in the DIEs - if 
> code is always in a known/assumable segment then why can you vary 
> segment for low_pc/high_pc/ranges?)

No, the spec says what it says.   There are no restriction on where code 
or data are located.

>     AFAIK, all addresses can be segmented addresses, except in the line
>     table where it isn't needed.
> 
>     Perhaps we should have (long ago) required flat/linear addresses for
>     x86
>     instead of segmented addresses.
> 
> 
> What's the line table's?segment_selector_size (in the DWARFv5 header) 
> for? (this sort of agrees and disagrees with you - it's there, but it's 
> not used in any part of the debug_line format that I can see)

It may be there for consistency across all headers.

> debug_addr supports segment selectors - in the debug_addr header it has 
> a field for "segment selector size" and the entries in the address list 
> are "segment/address pairs.".
> 
> So now there's two ways a segment selector for an address could be 
> specified - if you had a DW_TAG_subprogram with a DW_AT_low_pc using 
> addrx into a debug_addr with a non-zero segment selector and the 
> subprogram also had a DW_AT_segment, wonder which one's meant to win.

Again, FORM_addrx doesn't mean the same as DW_AT_segment.

They are orthogonal concepts.  Compression techniques, like FORM_addrx, 
should not be used to describe architectural features.

-- 
Michael Eager