default to strict dwarf-2 on powerpc-vxworks

[Olivier Hainque <hainque at adacore dot com>]

Hello,

On typical VxWorks environments, WindRiver integrated tools are used as
much if not more than gdb for debugging purposes.

These evolve at an industrial pace, traditionally not as fast as GCC
regarding the support of latest dwarf standards.

As of today, in our experience, the best compromise to let WRS debugging
tools work fine and have negligible effect on gdb's experience for this
target is to enforce strict dwarf-2 debugging info by default. 

We have been doing this in our production compilers for a while and find
it really useful, so we're happy to contribute here, in case this is deemed
more generally appropriate. 

The attached patch achieves this in two mini steps:

- Allow to distinguish between a dwarf version picked by default by the
  compiler and one provided on the command line that happens to match the
  default, which is useful to make sure we don't override a request for
  an explicit level on the command line.

  This is achieved by initializing dwarf_version to -1 instead of 2 from
  common.opt, then pick 2 as a default from toplev.c:process_options,
  similar to the scheme in place for dwarf_strict already.

- Default to dwarf_strict = 1 && dwarf_version = 2 for VxWorks via
  vxworks_override_options.

Sanity checked on mainline for powerpc-wrs-vxworks and bootstrapped
on x86_64-pc-linux-gnu.

Thanks in advance for your feedback,

With Kind Regards,

Olivier

2012-04-13  Olivier Hainque  <hainque@adacore.com>

	* common.opt (gdwarf-): Initialize dwarf_version to -1 instead of 2.
	* toplev.c (process_options): Default to dwarf_version 2.
	* config/vxworks.c (vxworks_override_options): Default to strict-dwarf
	and dwarf_version 2.

Attachment: vxdwarf.dif
Description: video/dv