Re: Documentation about debugging formats

[Robert Kiesling <kiesling at earthlink dot net>]

> Robert Kiesling wrote:
> 
> > How does GCC select which debugging format to use?  Pointers to some
> > info documents would be useful, or some specification of which format
> > gets used - is that system dependent, or simply which format provides
> > the most information?  There don't seem to be any actual info
> > documents about the formats, only info files about the bfd interfaces.
> > If there aren't any actual info documents about these formats, some
> > pointers to the relevant source code would be very helpful.
> 
> The default debugging format is defined by the target.  For example,
> look at gcc/config.gcc and you'll see that many targets list tm-dwarf2.h
> in their tm_file list, and tm-dwarf2.h contains
> 
> /* Enable Dwarf2 debugging and make it the default */
> #define  DWARF2_DEBUGGING_INFO 1
> #undef   PREFERRED_DEBUGGING_TYPE
> #define  PREFERRED_DEBUGGING_TYPE  DWARF2_DEBUG
> 
> This is just a shortcut for the common case, but each target can define
> this however it wants:
> 
> $ egrep 'define.*PREFERRED_DEBUGGING_TYPE' config/*.h
> config/chorus.h:#define PREFERRED_DEBUGGING_TYPE DWARF2_DEBUG
> config/darwin.h:#define PREFERRED_DEBUGGING_TYPE DBX_DEBUG
> config/darwin9.h:#define PREFERRED_DEBUGGING_TYPE DWARF2_DEBUG
> config/dbx.h:#define PREFERRED_DEBUGGING_TYPE DBX_DEBUG
> config/dbxcoff.h:#define PREFERRED_DEBUGGING_TYPE SDB_DEBUG
> config/elfos.h:#define PREFERRED_DEBUGGING_TYPE DWARF2_DEBUG
> config/interix.h:#define PREFERRED_DEBUGGING_TYPE DBX_DEBUG
> config/lynx.h:# define PREFERRED_DEBUGGING_TYPE DBX_DEBUG
> config/ptx4.h:#define PREFERRED_DEBUGGING_TYPE DWARF2_DEBUG
> config/sol2.h:#define PREFERRED_DEBUGGING_TYPE DBX_DEBUG
> config/tm-dwarf2.h:#define  PREFERRED_DEBUGGING_TYPE  DWARF2_DEBUG
> config/vx-common.h:#define PREFERRED_DEBUGGING_TYPE DWARF2_DEBUG
> 
> The debugging format also depends on things outside of the control of
> gcc, such as the assembler.  For example on PE platforms like Cygwin and
> MinGW the default debugging format is stabs, however the GNU PE
> assembler supports Dwarf-2 as well so on those platforms you get stabs
> with -g but you can also use -gdwarf-2 to get Dwarf-2 debug info.  See
> also
> <http://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html#index-g-352>.

Okay, thanks.  Please excuse the newbie question, and which should get
me in the right direction.  I would, however, like to determine which
formats would be supported by an installed GCC.  I suppose I could
determine those by using a configure script and finding out which
debug options don't generate errors, but it would be much better,
ISTM, to do that at run time.  I would like to support things like
stack traces in a system independent manner.  GDB does not provide
a run-time library with that API, however.  I guess I should find
the bfd plugins useful for that, or add that to my wish list.  :_

Thanks again,

Robert

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