Re: dwarf 2.1 .debug_ranges

[Michael Eager <eager at mvista dot com>]

Richard Henderson wrote:
> 
> On Tue, Aug 07, 2001 at 07:23:52PM -0700, Michael Eager wrote:
> > > What about the idea for using DW_FORM_block instead of .debug_ranges?
> > > Surely debug size is still a consideration...
> >
> > We hashed this back and forth.  I think that we went through several
> > iterations on proposals before finally adopting the changes in
> > .debug_ranges.   Adding relocations was not seen as desirable.
> 
> What have relocations got to do with this?  Here I'm only talking
> alternate representations of the same data.

Sorry.  Working from memory rather than my notes on a long and extensive
discussion about non-contiguous programs.

> At present we have
> 
>         .4byte  .debug_ranges+N         # DW_AT_ranges, DW_FORM_data4
> 
>         .8byte  <begin label 1> - <base addr>
>         .8byte  <end label 1> - <base addr>
>         .8byte  <begin label 2> - <base addr>
>         .8byte  <end label 2> - <base addr>
>         .8byte  0
>         .8byte  0
> 
> This could just as easily be represented as
> 
>         .byte   32                      # DW_AT_ranges, DW_FORM_block1
>         .8byte  <begin label 1> - <base addr>
>         .8byte  <end label 1> - <base addr>
>         .8byte  <begin label 2> - <base addr>
>         .8byte  <end label 2> - <base addr>
> 
> which saves 19 bytes of space.  We could save even more if we had
> a way to inform that we don't need pointer-size bytes to represent
> the displacements.
> 
> Obviously you can't usefully use base address selection entries
> with this, but there are many cases in which they aren't needed.
> 
> Seems like it would take little effort for a debugger to get this
> range information from either .debug_ranges or DW_FORM_block.

There were a number of different alternative representations discussed. 
I'm sure that each has various advantages and disadvantages.
Unless there is some evidence that the method adopted using .debug_ranges 
does not work, I don't see a reason to revisit this issue.    

--
Michael Eager     eager@mvista.com	408-328-8426	
MontaVista Software, Inc. 1237 E. Arques Ave., Sunnyvale, CA  94085