RFR: 8033251: Use DWARF debug symbols for Linux 32-bit as default

[David Holmes]

On 29/03/2014 4:26 AM, Coleen Phillimore wrote:
>
> On 3/28/14 12:44 PM, Erik Helin wrote:
>> Hi Coleen,
>>
>> thanks for having a look at the patch!
>>
>> On 2014-03-28 17:30, Coleen Phillimore wrote:
>>>
>>> I thought you'd be able to remove the DEBUG_BINARIES logic with this
>>> change.  It appears there are no platforms left that use stabs with
>>> gcc.
>>
>> Yeah, I also noticed that this change enables cleanups in the
>> Makefiles. However, I think it is better to do these cleanups as a
>> second change after this one, what do you think?
>
> A cleanup CR is fine.

Unless the cleanup is coming "tomorrow" I disagree. What have now is 
comments that make no sense given the change that has been made. And as 
every defined platform seems to use -g we can get rid of all this 
per-platform logic and simply check for clang. All of which can be done 
without doing the DEBUG_BINARIES cleanup. Eg delete the per-platform 
flags and simply have, for example,

     # Override per-platform if the default -g doesn't suite
     OPT_CFLAGS += $(OPT_CFLAGS/$(BUILDARCH))
     ifeq ($(OPT_CFLAGS/$(BUILDARCH)),)
       ifeq ($(USE_CLANG), true)
         # Clang doesn't understand -gstabs
         OPT_CFLAGS += -g
       else
         OPT_CFLAGS += -gstabs
       endif
     endif


In the future this flag should also potentially be coming in via spec.gmk.

David

>>
>> On 2014-03-28 17:30, Coleen Phillimore wrote:
>>> Does this change add -g for saproc, adlc and jsig compilations also?
>> It seems like saproc uses SA_DEBUG_CFLAGS which only is being set if
>> DEBUG_BINARIES=true. If DEBUG_BINARIES is not true, then it seems like
>> we don't generate debug symbols (please correct me if I'm wrong).
>>
>> The above also seems to be the case for libjsig.so.
>>
>
> These seem broken, but I don't know the makefiles well enough to comment.
>
> I think this change is good.  People have been asking for it for years
> and now that the size problem with dwarf has been fixed, I'm glad you
> are making this change.
>
> Thanks,
> Coleen
>> Looking in make/linux/makefiles/adlc.make it seems like adlc is using
>> -g for GCC 3.3 or newer.
>>
>> Thanks,
>> Erik
>>
>>> Coleen
>>>
>>> On 3/28/14 12:12 PM, Erik Helin wrote:
>>>> Hi all,
>>>>
>>>> this patch changes the Linux Makefiles to use DWARF as the default
>>>> debug symbol format for Linux 32-bit instead of STABS. The main
>>>> arguments for using DWARF are:
>>>>
>>>>   - DWARF provides a superior debugging experience compared to STABS.
>>>>   - STABS support in GCC/GDB is in maintenance mode [0].
>>>>   - External tools (e.g. perf on Linux) often understands DWARF but not
>>>>     STABS.
>>>>   - Compilation on 32-bit Linux can make use of precompiled headers.
>>>>
>>>> Webrev:
>>>> http://cr.openjdk.java.net/~ehelin/8033251/webrev.00/
>>>>
>>>> Testing:
>>>> - Compiling with GCC 4.3.4, GCC 4.7.3 and GCC 4.8.1
>>>> - JPRT
>>>>
>>>> Thanks,
>>>> Erik
>>>>
>>>> [0]: https://sourceware.org/ml/binutils/2013-01/msg00028.html
>>>
>