[Soot-list] Lazy loading of .class files

[Eric Bodden]

Hi Niklas.

Actually Soot already has a mechanism for loading classes lazily.
Usually it loads only those classes whose name you provide on the
command line (the application classes) and the classes that those
classes depend on. My suggestion would be to just rely on that
mechanism and *not* use loadClassAndSupport. Instead use a Transformer
to hook into Soot.

Eric

On 2 January 2012 09:15, Niklas Therning <niklas at therning.org> wrote:
> Hi,
>
> I'm working on an ahead of time (AOT) compiler for java bytecode. What
> I'm doing is to compile java bytecode into LLVM bitcode and then use the
> LLVM tools and GCC to get an x86/arm/whatever object file that can be
> linked into a native executable. I'm basing the standard classes
> (java.*, javax.*, etc) on the Apache Harmony project and I've written a
> small runtime in C. As of now I'm able to produce x86/x86-64 Linux
> executables that work for simple Java programs. I'm also working on an
> Eclipse plugin which extends the Eclipse JDT with incremental
> compilation of Java to native code using my AOT compiler.
>
> I'm using Soot in the first stage (JVM byte code -> LLVM bitcode) since
> Soot's register based Jimple representation is closer to LLVM's bitcode
> representation than the byte code of the JVM. And I get Soot's
> optimization for free which is very nice! Here's how I'm initializing Soot:
>
>         soot.G.reset();
>         Options.v().set_output_format(Options.output_format_jimple);
>         Options.v().set_include_all(true);
>         Options.v().setPhaseOption("jap.npc", "enabled:true");
>         Options.v().setPhaseOption("jap.abc", "enabled:true");
>         Options.v().set_print_tags_in_output(true);
>         Options.v().set_allow_phantom_refs(true);
>         Options.v().set_soot_classpath(getSootClasspath(clazzes));
>
>         for (Clazz clazz : clazzes.list()) {
>             SootClass c =
> Scene.v().loadClassAndSupport(clazz.getClassName());
>             c.setApplicationClass();
>         }
>         Scene.v().loadNecessaryClasses();
>
> (clazzes handles the classpath entries and Clazz is a wrapper around a
> .class entry in a JAR file or a .class File in a directory)
>
> My problem is that the code above takes about 5 seconds on my machine.
> The JRE classes from Harmony are always loaded by the code above so even
> if I'm compiling a single .class file more than 3000 .class files from
> Harmony have to be loaded by Soot. I would like Soot to load the
> required classes lazily when they are needed. This is especially
> important when I run the compiler from within my Eclipse plugin.
>
> I've tried to replace the loop and call to loadNecessaryClasses() above
> with the following code:
>
>         for (Clazz clazz : clazzes.list()) {
>             SootClass c = Scene.v().loadClass(clazz.getClassName(),
> SootClass.DANGLING);
>             c.setApplicationClass();
>         }
>
> That doesn't work out of the box so I've patched Soot 2.4 in a few
> places. I had to change the checkLevel() method in SootClass to
>
>     public void checkLevel( int level ) {
>         if( resolvingLevel < level ) {
>             SootResolver.v().resolveClass(this, level);
> //            String hint = "\nIf you are extending Soot, try to add the
> following call before calling soot.Main.main(..):\n" +
> //
> "scene().addBasicClass("+getName()+","+levelToString(level)+");\n" +
> //                          "Otherwise, try whole-program mode (-w).";
> //            throw new RuntimeException(
> //                "This operation requires resolving level "+
> //                levelToString(level)+" but "+name+
> //                " is at resolving level
> "+levelToString(resolvingLevel) + hint);
>         }
>     }
>
> The problem is that even though Soot doesn't complain any longer and I
> get Jimple code out of Soot the Jimple looks different and behaves
> differently when run than what I get when I use the slower initialization.
>
> So, how can I patch Soot to make lazy loading of required classes
> possible without changing the produced Jimple? I know too little yet
> about the Soot code to work this out on my own. Any help would be much
> appreciated.
>
> Regards,
> Niklas Therning
>
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-- 
Eric Bodden, Ph.D., http://bodden.de/
Head of Secure Software Engineering Group at EC SPRIDE
Principal Investigator in Secure Services at CASED
Tel: +49 6151 16-75422    Fax: +49 6151 16-72051
Room 3.2.14, Mornewegstr. 30, 64293 Darmstadt