What is bytecode verifier

As a final step the verifier also performs a data-flow analysis, which makes sure that no instruction reference any uninitialized local variables. Alternatively you might like to give it a look at the Java Language Environment white paper by James Gosling. The bytecode verifier traverses the bytecodes, constructs the type state information, and verifies the types of the parameters to all the bytecode instructions.

The illustration shows the flow of data and control from Java language source code through the Java compiler, to the class loader and bytecode verifier and hence on to the Java virtual machine, which contains the interpreter and runtime system.

The important issue is that the Java class loader and the bytecode verifier make no assumptions about the primary source of the bytecode stream--the code may have come from the local system, or it may have travelled halfway around the planet.

The bytecode verifier acts as a sort of gatekeeper: it ensures that code passed to the Java interpreter is in a fit state to be executed and can run without fear of breaking the Java interpreter. Imported code is not allowed to execute by any means until after it has passed the verifier's tests. Once the verifier is done, a number of important properties are known:. While all this checking appears excruciatingly detailed, by the time the bytecode verifier has done its work, the Java interpreter can proceed, knowing that the code will run securely.

Knowing these properties makes the Java interpreter much faster, because it doesn't have to check anything. There are no operand type checks and no stack overflow checks. The interpreter can thus function at full speed without compromising reliability.

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Learn more. Encyclopedia of Cryptography and Security Edition. Editors: Henk C. Contents Search. Bytecode Verification. Authors Authors and affiliations Jean-Louis Lanet. Get hold of all the important Java Foundation and Collections concepts with the Fundamentals of Java and Java Collections Course at a student-friendly price and become industry ready.

Uninitialized Variables Access rules for private data and methods are not violated. Method calls match the object Reference. There are no operand stack overflows or underflows. The arguments to all the Java Virtual Machine instructions are of valid types. Ensuring that final classes are not subclassed and that final methods are not overridden Checking that all field references and method references have valid names, valid classes, and a valid type descriptor. However, we can disable these checks using java -noverify VerifyGeekFile One might think how a program could have been manipulated since compiler checks these above validations before generating.

But the class file is vulnerable to change before JVM loads it. The interpreter can thus function at full speed without compromising reliability. Javatpoint Services JavaTpoint offers too many high quality services. What is the need of java bytecode verifier?