RFR: 8065656: Use DWARF debug symbols for Solaris

[Peter B. Kessler]

I don't think I invented the stab format.  I think stab.h came with adb and sdb, but might predate even those.  Stab.h covers the basics of global symbols, procedures, source files, line numbers, etc.  (The earliest copy I can find is http://svnweb.freebsd.org/csrg/include/stab.h?revision=12194&view=markup)

I probably did invent the N_PC (0x30) stab variant for the Berkeley Pascal compiler.  The trick there was that, rather than having to negotiate for some modest number of the limited (< 2 bytes) available space for stab entries, to claim only one entry for all the Pascal symbolic information and put all the information I needed into the string part of the "symbol".  That left lots of room for other languages, and separated the Pascal compiler (and all the other languages) from having to edit stab.h as we figured out what we wanted in the way of debugging information.  Maybe that is the origin of the "symbol table in the string" (stabs) idea.

That said, I'm happy to see stabs replaced by something better.

I'm also not an upper-case R reviewer.

			... peter
     
On 11/21/14 01:42 PM, Srinivas Ramakrishna wrote:
>
> What does Peter think? For those too young to remember, Peter invented stabs way back when he was a young grad student at Berkeley :-)
> It has given admirable service, like so much else he has touched!
>
> -- Ramki
>
> ysr1729
>
>> On Nov 21, 2014, at 08:30, charlie hunt <charlie.hunt at oracle.com> wrote:
>>
>> Looks good, though I am not an official (R)eviewer.
>>
>> Charlie
>>
>>> On Nov 21, 2014, at 9:30 AM, Erik Helin <erik.helin at oracle.com> wrote:
>>>
>>> Hi all,
>>>
>>> this patch changes the debug symbols format on Solaris from STABS
>>> [0] to DWARF [1] for libjvm.so. Since the supported compiler on Solaris
>>> has been updated to Oracle Solaris Studio 12.3 [2], the STABS debug format
>>> is now deprecated in the supported compiler [3]:
>>>
>>> -xdebugformat=stabs generates debugging information
>>> using the stabs standard format. The stabs format is no
>>> longer supported.
>>>
>>> Furthermore, in Oracle Solaris Studio 12.4, the release notes says [4]:
>>>
>>> The –xdebugformat=stabs for all compilers might be removed in a future
>>> release. The only debugger format option will be –xdebugformat=dwarf,
>>> which is currently the default.
>>>
>>> So, it seems to be a good time to change the debug format to DWARF when
>>> compiling with Oracle Solaris Studio. I also changed the debug format for
>>> GCC on Solaris to be DWARF, since the STABS support in GCC is in
>>> maintenance mode [5].
>>>
>>> More reasons for using DWARF instead of STABS are:
>>> - Better support by Oracle Studio Performance Analyzer (the performance
>>> team have requested that we use DWARF v2 or later instead of STABS).
>>> - DWARF provides a better debugging experience for C++ compared to STABS.
>>>
>>> The one drawback of using DWARF compared to STABS is that the size of the
>>> debuginfo increases. For a SPARC fastdebug build the size of
>>> libjvm.debuginfo built with STABS is 782 MB and with DWARF 1002 MB.
>>>
>>> To summarize, we need to change from STABS to DWARF because STABS is
>>> deprecated in 12.3 (even "more" deprecated 12.4 given the wording in the
>>> release notes). I would suggest to change sooner rather than later, given
>>> that the change to DWARF also brings Oracle Studio Performance Analyzer
>>> support as well as a better C++ debugging experience in dbx.
>>>
>>> Webrev:
>>> http://cr.openjdk.java.net/~ehelin/8065656/webrev.00/
>>>
>>> Bug:
>>> https://bugs.openjdk.java.net/browse/JDK-8065656
>>>
>>> Testing:
>>> - Compiled with Oracle Solaris Studio 12.3 on both Solaris 11.1 on SPARC
>>> and Solaris 11.1 on x86-64 using JPRT.
>>> - Verified that DWARF v2 symbols are produced with objdump.
>>>
>>> Thanks,
>>> Erik
>>>
>>> [0]: http://www.sourceware.org/gdb/onlinedocs/stabs.html
>>> [1]: http://www.dwarfstd.org/
>>> [2]: http://mail.openjdk.java.net/pipermail/jdk9-dev/2014-October/001489.html
>>> [3]: https://docs.oracle.com/cd/E24457_01/html/E22003/cplusplus.1.html
>>> [4]: https://docs.oracle.com/cd/E37069_01/html/E37070/gnxfn.html
>>> [5]: https://sourceware.org/ml/binutils/2013-01/msg00028.html