Why GCJ won't load my plugin when compiling bytecode?

Why GCJ won't load my plugin when compiling bytecode?

[Li junsong]

Hi there,

I have a java source code Welcome.java, and my plugin's name is findvar.so.
To avoid things getting complex, I write a very simple plugin,
printing out Hello
when loaded(printing hello in initial function).

My plugin can be loaded if GCJ compiles source code to native machine code,
that is if I type:
                   gcj-4.6 -fplugin=findvar.so Welcome.java --main=Welcome
Hello is then output to screen, and a.out is produced.

But it won't work if GCJ compiles source code to java bytecode
                   gcj-4.6 -fplugin=findvar.so -C Welcome.java --main=Welcome
Nothing is promoted, only Welcome.class is produced.


Does that mean that GCJ doesn't support -C and -fplugin at the same time?

I really appreciate your answer.

J. Li

Re: Why GCJ won't load my plugin when compiling bytecode?

[Andrew Pinski]

On Fri, Sep 9, 2011 at 1:56 PM, Li junsong <ljs.darkfish@gmail.com> wrote:
> Does that mean that GCJ doesn't support -C and -fplugin at the same time?

Because the source to byte-code conversion is done by ECJ (Eclipse's
java compiler) and not really done by a GCC front-end.
Thanks,
Andrew Pinski

Re: Why GCJ won't load my plugin when compiling bytecode?

[Li junsong]

On Fri, Sep 9, 2011 at 11:03 PM, Andrew Pinski <pinskia@gmail.com> wrote:
> On Fri, Sep 9, 2011 at 1:56 PM, Li junsong <ljs.darkfish@gmail.com> wrote:
>> Does that mean that GCJ doesn't support -C and -fplugin at the same time?
>
> Because the source to byte-code conversion is done by ECJ (Eclipse's
> java compiler) and not really done by a GCC front-end.
> Thanks,
> Andrew Pinski
>

Thanks, Andrew.

I want to do some optimization to reduce the allocation of java objects.

The reason why I need to compile java source code to .class file is that I need
stack information to see the information about java objects
allocation. The only
way (I know) to measure results of the optimization is to use Sun Java
VM, which
can produce profiles at runtime.

I chose gcj to write plugin to do optimization. So I need its .class
files output, but
not its binary code.

If I do not get it wrong, it means that If I want to do such
optimization and measure
the outcome, I have to look for other compilers, ( since GCC plugins
won't work ) right?

Thanks,
J. Li

Re: Why GCJ won't load my plugin when compiling bytecode?

[Bryce McKinlay]

On Fri, Sep 9, 2011 at 10:57 PM, Li junsong <ljs.darkfish@gmail.com> wrote:

> I chose gcj to write plugin to do optimization. So I need its .class
> files output, but not its binary code.

Modern versions of gcj only compile .class files to object code. gcj
doesn't directly compile Java source code, nor generate bytecode.
(early versions of gcj did do these things, but it was changed years
ago)

When you give it .java source files, gcj actually first calls out to
regular java compiler, then compiles the resulting .class files. You
can see the commands its running by adding -v to your command line.

> If I do not get it wrong, it means that If I want to do such
> optimization and measure
> the outcome, I have to look for other compilers, ( since GCC plugins
> won't work ) right?

That's right. A gcc plugin will never have a chance to run when using
"gcj -C" because the gcc compiler itself is not run.

Bryce

Re: Why GCJ won't load my plugin when compiling bytecode?

[Li junsong]

On Sat, Sep 10, 2011 at 12:24 AM, Bryce McKinlay <bmckinlay@gmail.com> wrote:
> On Fri, Sep 9, 2011 at 10:57 PM, Li junsong <ljs.darkfish@gmail.com> wrote:
>
>> I chose gcj to write plugin to do optimization. So I need its .class
>> files output, but not its binary code.
>
> Modern versions of gcj only compile .class files to object code. gcj
> doesn't directly compile Java source code, nor generate bytecode.
> (early versions of gcj did do these things, but it was changed years
> ago)
>
> When you give it .java source files, gcj actually first calls out to
> regular java compiler, then compiles the resulting .class files. You
> can see the commands its running by adding -v to your command line.
>
>> If I do not get it wrong, it means that If I want to do such
>> optimization and measure
>> the outcome, I have to look for other compilers, ( since GCC plugins
>> won't work ) right?
>
> That's right. A gcc plugin will never have a chance to run when using
> "gcj -C" because the gcc compiler itself is not run.
>
> Bryce
>

Thank you so much!

Now I know it. But I'm just wondering if others would make the same mistakes.

Unless people put his questions in this mail list, he would get no chance
to find out these informations. I mean, I have referred to the GNU java homepage
( which told me they had been merged with project GNU ClassPath),
gcc internals(in which the chapter "Java Tree" is blank ! ), the "ecj stuff"(
There're lots of error in gcj when the first time I compiled my new
gcc 4.6), But I find
few resources talking about gcj "internals".

So, If there is any thing I can do, apart from putting the question I
met on my blog to
tell others "don't make the same mistake again", please just let me know.

Thanks,
J. Li

Re: Why GCJ won't load my plugin when compiling bytecode?

[Alan Eliasen]

On 09/09/2011 04:24 PM, Bryce McKinlay wrote:
> Modern versions of gcj only compile .class files to object code. gcj
> doesn't directly compile Java source code, nor generate bytecode.
> (early versions of gcj did do these things, but it was changed years
> ago)

       Is this a permanent decision?  Is there any intention to make gcj 
compile from java source code again?

    Can anyone give me pointers to where this was decided upon and 
announced?  I'm curious to see the discussion.

-- 
   Alan Eliasen
   eliasen@mindspring.com
   http://futureboy.us/

Re: Why GCJ won't load my plugin when compiling bytecode?

[Mark Mielke]

On 09/11/2011 08:49 PM, Alan Eliasen wrote:
> On 09/09/2011 04:24 PM, Bryce McKinlay wrote:
>> Modern versions of gcj only compile .class files to object code. gcj
>> doesn't directly compile Java source code, nor generate bytecode.
>> (early versions of gcj did do these things, but it was changed years
>> ago)
>
>       Is this a permanent decision?  Is there any intention to make 
> gcj compile from java source code again?
>
>    Can anyone give me pointers to where this was decided upon and 
> announced?  I'm curious to see the discussion.
>

Doesn't seem like years but maybe... Java 5. Support for generics and 
such. Continue enhancing an alternative compiler with limited 
contributors, or use of that is basically guaranteed to be supported 
(Eclipse's compiler). I wasn't part of the decision - only an observer - 
but it seemed like an excellent decision when it was made, and I don't 
see why it isn't an excellent decision still.

Cheers,

-- 
Mark Mielke<mark@mielke.cc>

Re: Why GCJ won't load my plugin when compiling bytecode?

[Bryce McKinlay]

On Mon, Sep 12, 2011 at 1:49 AM, Alan Eliasen <eliasen@mindspring.com> wrote:
> On 09/09/2011 04:24 PM, Bryce McKinlay wrote:
>>
>> Modern versions of gcj only compile .class files to object code. gcj
>> doesn't directly compile Java source code, nor generate bytecode.
>> (early versions of gcj did do these things, but it was changed years
>> ago)
>
>      Is this a permanent decision?  Is there any intention to make gcj
> compile from java source code again?
>
>   Can anyone give me pointers to where this was decided upon and announced?
>  I'm curious to see the discussion.

http://gcc.gnu.org/ml/java/2007-01/msg00027.html

http://gcc.gnu.org/java :

January 8, 2007
We've merged the gcj-eclipse branch to svn trunk. The merge changes
gcj to use the Eclipse compiler as a front end, enabling all 1.5
language features. This merge also brings in a new, generics-enabled
version of Classpath, including some new tools. This new code will
appear in GCC 4.3.

June 6, 2006
RMS approved the plan to use the Eclipse compiler as the new gcj front
end. Work is being done on the gcj-eclipse branch; it can already
build libgcj. This project will allow us to ship a 1.5 compiler in the
relatively near future. The old gcjx branch and project is now dead.