Re: [patch] Fix oddity in personality routine

Jack Howarth wrote:
> On Tue, Nov 17, 2009 at 02:54:53PM +0000, Andrew Haley wrote:
>> Jack Howarth wrote:
>>> On Tue, Nov 17, 2009 at 10:58:00AM +0000, Andrew Haley wrote:
>>>> Jack Howarth wrote:
>>>>> On Mon, Nov 16, 2009 at 07:08:49PM +0000, Andrew Haley wrote:
>>>>>> There's another unwinder?  Gosh.
>>>>>>
>>>>>> Set a bp on '_Jv_Throw' and step through.  You'll need to compile libgcc
>>>>>> with -O0 or you'll go insane.  The unwinder is quite complex, and it takes
>>>>>> a fair while to understand it.
>>>>>    I have added an unwinder_walk.txt attachment to PR41991. It is a walk
>>>>> from the _Jv_Throw breakpoint for ecj1 compiling the testme.java test code
>>>>> with a libgcc compiled with -O0 installed. This is with current gcc trunk
>>>>> using the patch from http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41991#c3
>>>>> compiled on x86_64-apple-darwin9.8.0 to make sure that the FSF libgcc is
>>>>> used. Hopefully a fix can be found in the libjava code that calls the
>>>>> unwinder as fixing this within the unwinder won't help us with darwin10
>>>>> or later.
>>>> There's probably nothing wrong with the libjava code that calls the
>>>> unwinder: after all, it works everywhere else.  I'm betting this is
>>>> bad unwind info.
>>>>
>>>> Anyway, at least this is a start.  It tells us that the stack is
>>>> walked but no landing pad is found.  We don't know why.
>>>   In the unwinder walk, are there any particular places where I could
>>> get additional debug information in gdb that would be helpful to diagnose this
>>> issue?
>> Sure.  The trace you provided is very incomplete, and in particular
>> I can't see any stepping into _Unwind_RaiseException.
>>
> Andrew,
>    One question about the absence of stepping into _Unwind_RaiseException.
> Am I doing the walk incorrectly? The steps I used were...
> 
> 1) gdb /sw/lib/gcc4.5/libexec/gcc/x86_64-apple-darwin9.8.0/4.5.0/ecj1
> 2) (gdb) break _Jv_Throw
> 3) r testme.java -fbootclasspath=./:/sw/lib/gcc4.5/share/java/libgcj-4.5.0.jar -fsource=1.5 -ftarget=1.5 -fzip-dependency /var/folders/1C/1CdoNxmNFHyOIjNBLNuJh++++TM/-Tmp-//ccnFt6vF.zip -fzip-target /var/folders/1C/1CdoNxmNFHyOIjNBLNuJh++++TM/-Tmp-//ccrNgp0M.jar
> 4) (gdb) s
> 5) repeatedly hit return to continue stepping through the code
> 
> Is there something wrong with that approach which would have kept me
> from walking into Unwind_RaiseException?

Sometimes it doesn't work, so you have to be inventive.  Try
setting a breakpoint on Unwind_RaiseException, or step a single
instruction at a time when you get to a call.

> I assume that gcc trunk's
> debug code is still compatible with Apple's gdb. If not, I do have
> a build of gdb 7.0 on Intel darwin that I can use instead. Thanks
> in advance for any hints on this issue.
>               Jack
> ps I do notice that gdb can't find the object files from /sw/src/fink.build/gcc45-4.4.999-20091116/darwin_objdir/x86_64-apple-darwin9.8.0/libjava/.libs/libgcj.lax so it might have problems with debugging within libgcj. If I recall correctly this .lax issue is known...
> 
> http://gcc.gnu.org/ml/gcc/2008-10/msg00083.html

Ouch.  That will cause gdb breakage, for sure.

Andrew.