Why are JSR/RET deprecated Java bytecode?

问题:

Does anyone know why the JSR/RET bytecode pair is deprecated in Java 6?

The only meaningful explanation I found on the net was that they made code analysis by the runtime harder and slower to perform. Does anyone know another reason?

回答1:

JSR and RET make bytecode verification a lot more difficult than it might otherwise be due to the relaxation of some normal bytecode constraints (such as having a consistent stack shape on entry to a JSR). The upside is very minor (potentially slightly smaller methods in some cases) and the continuing difficulties in the verifier dealing with odd JSR/RET patterns (and potential security vulnerabilities, and the associated runtime cost of full verification) make it a non-useful feature to continue having.

Stack maps and the lighter-weight verifier that is enabled as a result of the data are a big performance win during class loading for no sacrifice in safety.