Re: stabs changes for 64 bit targets

[David Edelsohn <dje.gcc@gmail.com>]

On Tue, May 14, 2013 at 10:38 AM, David Taylor <dtaylor@emc.com> wrote:
> Jakub Jelinek <jakub@redhat.com> wrote:
>
>> On Mon, May 13, 2013 at 10:45:46AM -0400, David Taylor wrote:
>> > There are problems when using current STABS debug format for 64 bit
>> > targets.
>>
>> Why are you considering extending STABS at this point?
>> STABS support might very well be dropped altogether from GCC 4.9 or the next
>> release, people just should use DWARF[234] everywhere.
>
> There are multiple reasons.  One of the big reasons is...
>
> Prior to GCC 4.7, DWARF is too verbose compared to STABS.
>
> In STABS, all strings go into the string table; identical strings get
> put into the table just once.
>
> In DWARF, prior to GCC 4.7, macro strings do not go into the string
> table.  If 1000 files all include a given header file, each #define in
> that header gets its own string in the debug information -- so the
> string is present 1000 times.  GCC 4.7 (DWARF4) fixes this.
>
> We have STABS extensions (posted years ago, but never merged) that
> record macros in the STABS debug information -- at the -g3 level, just
> like for DWARF.

Please keep in mind that AIX continues to use STABS with its XCOFF
file format, so please do not make changes to STABS under the
assumption that you are the only producer and consumer.

AIX added support for DWARF and I believe that there are some patches
to support DWARF on AIX from Adacore, but those have not been merged
into FSF GCC, Binutils and GDB yet.

Thanks, David