Re: [PING][PATCH,DWARF,gfortran] Change DWARF-2 output for Fortran COMMON symbols

[George Helffrich <george at geology dot bristol dot ac dot uk>]

A similar problem arises with .stabs debug information -- for the long 
answer, please see the discussion linked from

http://gcc.gnu.org/ml/gcc-patches/2004-08/msg02475.html

Briefly, it not possible to fix this in GDB.  The problem lies in 
Darwin loader, which refuses to relocate references like SYM+offset in 
non .text sections -- a design decision unlikely to be changed by 
Apple.  To relocate symbols in .comm, Apple's GDB for Darwin gets 
around this restriction by assuming that every DWARF symbol reference 
is either 1) a symbol whose name is the name of the .comm section; 
otherwise 2) an offset into the .text section.  Assumption (1) is valid 
for C, but not for Fortran -- the program symbol is not the .comm 
section name in Fortran (not even a mangled form).  By explicitly 
declaring the symbol's membership in .comm through DW_TAG_common, it 
averts the problem in a compatible way by naming the .comm section 
involved independently from the program's symbol.  This is the same 
spirit as the workaround proposed, in another patch, for .stabs 
behavior.

This only affects Fortran, and this patch only changes the behavior for 
gfortran-compiled code.  It also uses a DWARF feature designed for 
Fortran in a way that (non-Apple) GDB already handles properly, so it 
seems clear and straightforward to use it, even if the motivation is a 
Darwin loader workaround.

                                                                        
     George Helffrich