Re: NullPointerException throwed when running GCJ

[David Daney <ddaney@caviumnetworks.com>]

On 12/29/2010 12:01 AM, majia gm wrote:
> 2010/12/29 David Daney<ddaney@caviumnetworks.com>:
>> Adding java@... as this is where java questions are handled.
>>
>> On 12/28/2010 07:05 AM, majia gm wrote:
>>>
>>> Hi, everyone.
>>>
>>> I'm porting GCJ to a non-mainstream platform, which is a RISC machine
>>> with some similarity to ARM.
>>> The GCC I'm using is version 4.4.2. I start the porting from ARM's code.
>>>
>>
>> There is quite a bit of work involved in getting libgcj running on a new
>> target.  One thing that is obvious from your stack trace is that the stack
>> unwinding code is not decoding the instruction pointer properly. That would
>> be one place to start.
>>
>> Unfortunatly, there isn't really one specific thing we can point you to.
>>   You will probably have to step through things with GDB and make sure that
>> are the target specific code is doing the right thing.
>>
>> The boehm-gc may need porting as well.  Actually I might start with
>> boehm-gc, I think it has its own test suite, so it can be debugged
>> separately.
>>
>> Then look at all the target specific code for a known working target (arm,
>> mips, x86, etc...) and try to verify that your target code functions
>> correctly.
>>
>> Good Luck,
>> David Daney
>>
>>
>>
>>> When running the GCJ on the target platform, it mentioned that the ECJ
>>> is needed. I don't know whether GCJ can live without ECJ, so I
>>> donwload the latest ECJ jar file and recompiled.
>>>
>>> When running GCJ to compile a JAVA source file, I got the following error.
>>>
>>> [root@localhost pxx]# gcj -C HelloWorld.java -v
>>> Using built-in specs.
>>> Target: unicore32-linux
>>> Configured with: /home/vhome/FengYi/pxx/mydir/gcc-4.4.2/configure
>>> --host=unicore32-linux --target=unicore32-linux --prefix=/usr
>>> --build=i686-redhat-linux-gnu --enable-clocale=gnu --enable-shared
>>> --enable-threads=posix --enable-__cxa_atexit --enable-languages=java
>>> --with-gnu-ld --disable-libstdcxx-pch --disable-multilib
>>> --with-pkgversion=UC4_1.0_gama_20101228
>>> Thread model: posix
>>> gcc version 4.4.2 (UC4_1.0_gama_20101228)
>>> COLLECT_GCC_OPTIONS='-fsaw-java-file' '-C' '-v'
>>> '-fbootclasspath=./:/usr/share/java/libgcj-4.4.2.jar' '-g1'
>>> '-fsyntax-only' '-femit-class-files' '-S' '-o' 'NONE' '-shared-libgcc'
>>>   /usr/libexec/gcc/unicore32-linux/4.4.2/ecj1 HelloWorld.java -g1
>>> -fbootclasspath=./:/usr/share/java/libgcj-4.4.2.jar -g1 -fsource=1.5
>>> -ftarget=1.5 -fzip-dependency /tmp/ccTF9EKh.zip
>>> Exception in thread "main" java.lang.ExceptionInInitializerError
>>>     at 0x1(Unknown Source)
>>>     at 0x3(Unknown Source)
>>>     at 0x5(Unknown Source)
>>>     at 0x5(Unknown Source)
>>>     at 0x5(Unknown Source)
>>>     at 0x5(Unknown Source)
>>>     at 0x5(Unknown Source)
>>>     at 0xffffffffffffffff(Unknown Source)
>>>     at 0x2(Unknown Source)
>>>     at 0xffffffffffffffff(Unknown Source)
>>>     at 0xffffffffffffffff(Unknown Source)
>>> Caused by: java.lang.NullPointerException
>>>     at 0x1(Unknown Source)
>>>     at 0x5(Unknown Source)
>>>     at 0x4(Unknown Source)
>>>     ...9 more
>>>
>>>
>>> Could anyone give me some hints on how could this happen?
>>> I really appreciate you patience.
>>>
>>
>>
>
> Hi, David.
>
> Thank you for your reply. It's very nice of you.
>
> When metioned to the stack unwinding code, do you mean the file
> backtrace.h in libjava/sysdeps/arch? It seems some archs don't have
> this file. And ARM has this file, but seems it takes over little
> works.
>

Before java can work, you need to make sure that your GCC can correctly 
compile C and C++ code.  Specifically all GCC testsuite C and C++ tests 
that deal with exception handling must pass.

libgcj as a normal part of its startup processing will throw and catch 
several exceptions.  If the exception handling machinery is not working 
you will never get to your programs main() method.

Before trying to get your own programs working, you should be able to 
run the libjava testsuite and have the majority of the the tests pass.



> Actually, the current status of my porting is as follows. I tried gij
> successfully on the target to interpret a simple class file
> HelloWorld.class which is compiled through a x86-gcj on a x86 machine.
> And the gcj on the target also works well to compile the source file
> HelloWorld.java into native executable file. But it fails to compile
> HelloWorld.java into HelloWorld.class through gcj on the target. My
> GCC version is 4.4.2, and the ecj I used is the latest.
>
> I found that when compiling Java sources into class file, the x86-gcj
> use the jc1 instead of ecj.
> The following two questions confusing me. Can gcj live without ecj?
> What's the difference between ecj and jc1? I googled and got little.
>

ecj: .java -> .class
jc1: .class -> .s (assembly)
as:  .s -> .o (linkable object code)
ld:  .o -> executable program.

The gcj driver program runs the required sequence of these to obtain the 
requested result.

> If you could give me some hints, I would really appreciate.
>
> Thank you.
> Gmmajia
>