Re: Fortran Common Blocks

[Michael Eager <eager at eagercon dot com>]

Oops.  I forgot that the common name is global, but the elements are local.

James Cownie wrote:
> 
> > I'm sure that there are folks with much better knowledge of Fortran than
> > I, but my first thought is that common blocks are global, not local
> > to a subroutine.  This suggests to me that the DW_TAG_common_block should
> > be a sibling of DW_TAG_subprogram, not a child.
> 
> AAArrrggghhhh _no_. Common blocks should be local to a subroutine.
> 
> Conside legal (if ill advised) FORTRAN like this
> 
>       subroutine foo
>       integer i
>       real r
>       common /madman/ i, r
> C ... etc ...
>       end
> 
>       subroutine bah
>       integer i
>       real r
>       common /madman/ r, i
> C ... etc ...
>       end
> 
> If you're going to debug this properly you'd better have two separate
> and properly scoped instances of the common block definition for
> "madman".
> 
> This example is clearly nutty, but there are older f77 codes which
> do exactly this kind of thing (particularly with blank common) to
> reduce their store requirements by sharing the same space for
> temporary arrays.
> 
> As to what's wrong with the dwarf, that's less clear to me.
> 
> It looks OK to me, though you need a DW_TAG_common_inclusion to
> actually state that the common block is being used in a subroutine.
> 
> Common blocks should certainly own variables...
> 
> -- Jim
> 
> James Cownie    <jcownie@etnus.com>
> Etnus, Inc.     +44 117 9071438
> http://www.etnus.com


-- 
Michael Eager	 Eager Consulting     eager@eagercon.com
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