byte code

Furthermore, due to a novel approach to bytecode verification, we're also able to ensure runtime type safety of the compiled code.

Pattern detectors are a good choice when what you're trying to detect can be expressed as a sequence of bytecode patterns.

There used to be a time when people went nuts on hearing the phrase "bytecode manipulation" .

This code is in the form of instructions for the JVM, generally called bytecode, which is one of the topics for the next section.

How much of an applications code is turned into bytecode depends on a couple of factors.

Note, however, that this doesn't convert the Perl into C, it just embeds Perl bytecode into a C-based application.

Due to the high computational overhead of this operation, however, MIDP VMs do not perform complete bytecode verification at runtime.

I'll return to this point later in the article when I discuss some of the details of the bytecode generation.

After all, someone could have changed the bytecode manually with a hex editor to attempt to trigger a buffer overflow.

The bytecode that makes up the executable portion of the class file is actually machine code for a special kind of computer -- the JVM.

Even with these security measures in place, not all code that passes bytecode verification should be allowed to run.

These instructions take no arguments , so the bytecode definition would have to be extended to support the acquisition of multiple locks .

Due to standardization of C# and the Common Language Infrastructure, the bytecode is now officially known as CIL.

Some of the problems I ran into are specific to BCEL, but others apply to other bytecode frameworks as well.

One of the goals I ve set for the JiBX 2. 0 Development is to support source code enhancement as an alternative to bytecode enhancement.

You can either use a simple GUI interface or a console application to run the bytecode enhancements on your application class files.

The principle is true in the world of bytecode manipulation as well as in that of API design.

BCEL's implementation of bytecode handling also seems overly complex, with great flexibility but a large number of objects to manipulate.

Each instantiation of a mixin is compiled to a separate Java class; no sharing of bytecode occurs across copies.

One example is the name of method parameters and various generics type information, which get dropped moving from Java to bytecode.

As I mentioned back in The source of all bytecode, the source code used by Javassist is not exactly the Java language.

JIT typically causes a slight delay in initial execution of an application, due to the time taken to load and compile the bytecode.

This example includes several branches, with the bytecode for three branches shown in bold.

As with bytecode generation, the binding compiler will always generate the same source code token sequence for a binding component.

The bytecode verification process guarantees that an application cannot access memory spaces or use resources outside of its domain.

Retroweaver consists of two logical components: a bytecode enhancer and a runtime library.

But this translation is still conceptually trivial; the mapping from Java to Dalvik bytecode is smooth, by design.

The advantage of this approach is simplicity: The JRE developers need only write the code to handle each type of bytecode.

Even so, there are still substantial differences between the programming techniques used in source code and the bytecode equivalents.

I'll start with a look at the JiBX bytecode generation architecture.

Run some events through it, watch it load classes, compile bytecode, and of course, manage memory.

In the earlier article, I demonstrated how run-time bytecode generation can be used to replace reflection.

Listing 6 shows Java source code generated from the same list of abstract operations as used for the Listing 5 bytecode.

If it is, ProGuard automatically processes the application's bytecode before packaging everything into an . apk file.

Come back then for a look behind the curtains at the bytecode generation core of JiBX.

The first is a simple bytecode language that you can use to create scripts that you download into the unit.

Gretel uses calls to a static method to track executed blocks, adding these into the bytecode only where needed.

But FindBugs is different -- it uses bytecode analysis and a host of plug-in bug pattern detectors to find common bugs in code.

At runtime, the MIDP VM does a quick linear scan of the bytecode, matching each valid instruction with a proper stackmap entry.

After I added the stack state tracking, bytecode problems became traceable to a particular line of code.

Dsun. reflect. noInflation=true disables inflation entirely but, counterintuitively, causes bytecode accessors to be used for everything.

for frequently executed bytecode, JIT compilation is used to run at high speed, after an initial phase of slow interpretation.

The Perl compiler works by taking the generated bytecode and then outputting the results in a variety of different ways.

The only proviso is that the bytecode modifications should be deterministic and predictable.

Bytecode transformers can be run offline (compile time), at load-time, or dynamically at run-time (using JVMTI API).

The object code for a VM is also called bytecode, specifically defining an instruction set that an interpreter executes.

What this does is save Perl from having to compile the script from its source code into the bytecode each time.

Evan has added a JIT framework that can be enabled, along with a dynamically generated bytecode interpreter.

Either way, the new bytecode is passed as a Java-like source code statement or block in a String.

Utilize Javassist and CGLIB frameworks for generating new objects and for low-level, highly tuned bytecode transformation.

The optimizations performed by today's JVM are extraordinary, allowing byte code to outperform natively-compiled code in many cases.

The feature even supports integration with runtime bytecode modification, which this article discusses later.

Javassist again accepts the source code without complaint, but the resulting bytecode fails verification when I try to execute it.

In terms of bytecode, each parameter occupies one or more words of the stack frame in use when the method is executed.

JiBX data binding implements more complex code generation than most other frameworks using bytecode enhancement.

JiBX uses bytecode enhancement to add methods to compiled classes that convert instances of the classes to and from XML.

Object for a sequence of bytecode instructions being generated.

Handling source code generation in the same framework as bytecode generation promises to create some interesting new problems.

Despite this identical bytecode, the type parameter information is recorded in the class format using a new signature attribute.

AOP make bytecode changes normal, without requiring understanding of the class file format.

In normal usage, Java source code is translated into bytecode instruction sequences by a compiler.

Javassist does a great job of making classworking easy by letting you work with source code rather than actual bytecode instruction lists.

JITC - Just-In-Time Compiler that converts Java bytecode into the native machine code of the host architecture.

Source code method matching requires a little more work than bytecode method matching.

Disabling the JIT completely means that the JVM will run an application's Java bytecode in purely interpretive mode.

Clojure has already compiled the protocol you defined earlier into JVM bytecode representing this interface.

Depending on what you do in the source code, you can even get Javassist to generate invalid bytecode.

Javassist provides two separate ways to handle systematic bytecode modifications.

To keep the stack state valid , bytecode must take the differences between virtual and static methods - and the return type - into account .

Yes, we produce bytecode for the VM, which can optionally produce native code for several architectures.

Blue is interpreted, but can be compiled to bytecode for greater performance.

By converting Java bytecode into optimized machine code at runtime, it greatly increases the speed at which Java methods are run.

The AspectJ compiler builds AspectJ and Java code declared in ". java" or ". aj" files, and produces plain Java bytecode.

Lastly, Kilim's magic is enabled by a post process, called a weaver, that alters the bytecode of classes.

Most EJB CMP CMR solutions use code generation to implement persistence code, while JDO uses bytecode decoration.

Much of the time I've spent on JiBX development went to track down invalid bytecode generation problems.

In essence, I was implementing my own on-the-fly validator for the bytecode.

A bundle is a jar file that contains the application's bytecode and its resources.

Mr. Qi has experience in JVM internals, bytecode instrumentation, and Java programming .

Have them over to dinner, and swap stories of performance tricks on how to run Java bytecode as fast as possible.

If you use an Ant-style build procedure, there's no problem; you just add the Retroweaver bytecode enhancer as a step after the compile.

Before a . class file is loaded into the virtual machine, it is verified by a bytecode verifier and optionally a SecurityManager.

Listing 5 shows bytecode generated from the list of abstract operations shown in Listing 4.

Second, a bytecode dispatch is a single direct memory read, followed by a single indirect branch.

Provides JVM to run Java bytecode compiled elsewhere.

Because runtime class verification is computationally expensive for MIDP VMs, MIDP has a special two-step bytecode verification scheme.

we parse all of the bytecode and the corresponding source code to build up our representation of the software system (our Software DNA map).

Check back for the full details on working at the bytecode assembler level next month.

This is true, but it merely means that the work of referencing the class by its formal name falls to the compiler and bytecode.

For instance, bytecode can handle values that need to be used more than once by duplicating them on the stack.

The first Javassist technique for systematic bytecode modification uses the javassist. CodeConverter class.

The loading phase consists of locating the required class file (by searching though the respective classpaths) and loading in the bytecode.

Early (first generation) JVMs were basically interpreters for the virtual machine bytecode.

This aspect surrounds method calls with bytecode that creates and stops a StopWatch instance.

Getting the same effect by using Javassist to manipulate the class bytecode seems like it should be easy.

Fetches the next bytecode to execute.

To write bug detectors, you need some understanding of the structure of JVM bytecode and of class files.

It is convenient, if unsupported, and the compiler generates mostly compatible bytecode in a single pass.

Use it to generate your bytecode the old fashioned way - from Java source code.

Bytecode also treats method parameters similarly to local variables.

Therefore, executing a bytecode instruction is much faster than visiting a syntax tree node.

Remember that Scala compiles to Java bytecode, meaning that it runs on the JVM.

In fact, AOP can be seen as a high level language for bytecode manipulation.

Keeping frequently used scripts in bytecode form would give us a sizable performance boost.

By contrast, most classworking libraries bypass source code completely and only work at the bytecode level.

Turn Java language source code or compiled bytecode into native machine code with.

I'll start classworking coverage with the Javassist bytecode manipulation library.

Because creating the bytecode accessors is quite slow, the Java runtime can cache these accessors for later use.

A binary converter that transforms Java-language bytecode into MSIL.

The two classworking frameworks I cover in my earlier articles take very different approaches to working with bytecode.

Once your program is compiled to bytecode, you can compile it to native code.

The JIT compiler compiles Java bytecode to optimised native binary code at run time.

The code generation model was added to make the bytecode generation more modular and easier to maintain.

Javassist lets you work with source code, which it compiles into Java bytecode.

The Bytecode class details page shows the methods and fields that are defined and the classes that are used.

despite the added complexity of bytecode stack manipulation , it also offers some flexibility that is not available in source code.

Bytecode transformations with javassist. ExprEditor build on the same principles as those done using CodeConverter.

Because of this, it will generate bytecode from the source in ways that may have surprising results if you're not careful.

His research concerns the development of formal semantic models and extensions of the Java language, both at the source and bytecode levels.

For more detailed information on sharing modified bytecode, see the JVM diagnostics guide (see Resources).

Each event is encoded using a bytecode representation called ESAX (encoded SAX).

All bytecode scanning detectors are based on the visitor pattern, which FindBugs implements.

ASM: Get the ASM Java bytecode manipulation framework.

Creating the synchronized block yielded 16 lines of bytecode, whereas synchronizing the method returned just 5.

Another way to get fast executing code is to generate the JVM bytecode directly.

It's important to point out that Rubinius is using bytecode interpretation.

It doesn't require a code-generation phase, a bytecode-generation step, or a run-time bytecode-manipulation library.

This makes slicing and dicing your bytecode easy.

Bytecode instrumentation: This is the process of injecting bytecode into the application classes.

you do also get some features typical of bytecode languages , such as a string data type and garbage collection.

And since IKVM can do the bytecode translation "on the fly" , the effect feels fairly transparent to the CLR developer.

Once the scripts are compiled to normal Java bytecode they can be run by any standard JUnit runner.

However, you can decompile the Java bytecode if you are curious.

Next month I'll look at the ASM bytecode manipulation framework.

Instead, it just runs the bytecode that was generated.

These metadata files are used during the bytecode enhancing process and at run time.

Modified bytecode can be shared by using the modified= suboption to -Xshareclasses.

Do you want to try transforming methods, but are reluctant to start programming in bytecode?

The source code you write is compiled on the fly into the bytecode that is executed.

JiBX 1. 0 Uses the BCEL framework for bytecode manipulation.

Have you encountered any problems with other libraries that instrument bytecode?

Many people imagine Java is slow because it generates interpreted bytecode rather than native code.

BCEL, on the other hand, works directly with bytecode.

Bytecode instrumentation: modifying the bytecode of an application at runtime to inject performance collectors

The ASM plugin even produces the ASM code that can be used to generate the corresponding bytecode, as shown in Figure 2

Gives a commented version of the bytecode from the beginning of the

Some of the compile-time optimizations we're looking at, now that we have a bytecode representation, include

In part 2 he reviews post-compilation instrumentation, specifically through interception, class wrapping, and bytecode instrumentation

The full compilation mode is almost identical, except that instead of producing a Perl script with the compiled bytecode embedded in it,

For bytecode which is executed only a few times, this saves the compilation time and reduces the initial latency;

Advanced Heuristics for bytecode function deletion

Analysis of information flow in exception handling of Java bytecode

Optimizing algorithm of dynamic AOP based on bytecode transformation

To demonstrate the basic branch operation, Listing 3 shows the commented bytecode for the Listing 1

his research concerns the development of formal semantic models of java , and extensions of java , both at the source and bytecode levels

special support for bytecode frameworks like Javassist and cglib which are used by many other tools

Adds Copyright Notice to bytecode

Runs a compiled bytecode object

The JSR 14 target mode of javac causes the compiler to emit JDK 1. 4-compatible bytecode corresponding to Java 5 language features

Based on asmock-0. 3 (for bytecode generation and lowlevel execution handling)

To create this bytecode version, use the -B option to the perlcc command. For example