Re: Support for DDWARF-2 debug info? (on Cygwin)

[Brian Ford <ford@vss.fsi.com>]

Please CC me on replys.  I am not currently subscribed to any of these
lists.

I am interested in contributing to this endeavor, but I need help
with a few specific problems.  Any pointers or information about known
issues would be greatly appreciated.

I have built gcc 3.2.1 (just --enable-languages=c so far) with "#define
DWARF2_DEBUGGING_INFO 1" added to config/i386/cygwin.h.  The resulting
compiler still produces stabs by default, but will accept "-gdwarf-2".

When using "-gdwarf-2", the debug information is, I believe, correctly
output, but the sections have incorrect attributes as shown by the
"objdump -h" output below.  (BTW, I know I will need to modify the built
in link script for binutils so it knows where to put these sections)  The
incorrect section attributes keep the resulting executable from running, I
think.

Can anyone tell me how to get these attributes set correctly?  Is the
problem in gcc or binutils?  I imagine this is just the tip of the
iceberg, so know gotchas are welcome.

$ objdump -h test.o

test.o:     file format pe-i386

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         00000040  00000000  00000000  000001a4  2**4
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
  1 .data         00000000  00000000  00000000  00000000  2**4
                  ALLOC, LOAD, DATA
  2 .bss          00000000  00000000  00000000  00000000  2**4
                  ALLOC
  3 .debug_abbrev 0000015c  00000000  00000000  000001e4  2**2
                  CONTENTS, ALLOC, LOAD, DATA
  4 .debug_info   00001198  00000000  00000000  00000340  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
  5 .debug_line   00000158  00000000  00000000  000014d8  2**2
                  CONTENTS, RELOC, READONLY
  6 .debug_frame  00000034  00000000  00000000  00001630  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
  7 .debug_pubnames 0000001c  00000000  00000000  00001664  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
  8 .debug_aranges 00000020  00000000  00000000  00001680  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
  9 .debug_str    00000030  00000000  00000000  000016a0  2**2
                  CONTENTS, ALLOC, LOAD, DATA

I believe the .debug sections should be marked READONLY and DEBUGGING (as
they are in Solaris?), but not ALLOC, LOAD, or DATA.  Is this right?

Thanks.

On Sat, Jan 04, 2003 at 07:55:42PM -0000, Christopher Faylor wrote:
>On Sat, Jan 04, 2003 at 05:30:15AM -0000, Dave Hooper wrote:
>>a)  If the cygwin build of gcc/gdb/gas/etc supports DWARF-2 debug
>>information (it appears not but I may be overlooking something)
>
>It doesn't.
>
>>b)  If not, is it just a matter of #defining the appropriate flags in
>>/gcc/config/i386/cygwin.h and rebuilding gcc?
>
>No.  Code is needed in gcc.
>
>>c)  Whether DWARF-2 will become the standard debug info format for
>>cygwin builds of apps in the near future (as it already has for various
>>other platforms, e.g. djgpp).
>
>It would be nice to switch to Dwarf-2 but no one has has stepped forward
>to implement the required bits to handle this.  I don't remember what is
>required, unfortunately, but I have discussed it with gcc engineers.  If
>you're interested in working on this, asking in the gcc@gcc.gnu.org
>mailing list would probably be the place to start.
>

-- 
Brian Ford
Senior Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
Phone: 314-551-8460
Fax:   314-551-8444