spoto/it-univr-bcel

BCEL utilities for type inference and stack map manipulation

it-univr-bcel

BCEL utilities for inferring types in Java bytecode and for recomputing stack maps for a method. A stack map is compulsory from Java bytecode version 50 and higher. It specifies types at specific program points, ie., at targets of jumps. Compilers generate code with stack map tables, but code instrumentation might invalidate them. These utilities allow one to recompute stack map tables after code instrumentation with the BCEL library for bytecode instrumentation.

Type Inference

Given a BCEL MethodGen named m, this library allows one to infer the types at each of its instruction by computing

TypeInferrer inferrer = TypeInferrer.of(m);

Types at each instruction handle ih in m can then be accessed by using an intuitive API, as in the following example:

Types types = inferrer.getTypesAt(ih);
int stackHeight = types.stackHeight();
int localsCount = types.localsCount();
Type top = types.getStack(stackHeight - 1);
Type local0 = types.getLocal(0);

Stack-Map Inference

Given a BCEL MethodGen named m (with or without a stack map), this library allows one to infer a new stack map for m by computing

StackMapInferrer inferrer = StackMapInferrer.of(m);
Optional<StackMap> = inferrer.getStackMap();

The result is Optional since not all methods need a stack map.

Stack-Map Recomputation

Given a BCEL MethodGen named m (with or without a stack map), this library allows one to modify m by removing its old stack map (if any) and adding a new inferred stack map for it (if needed), by computing:

StackMapReplacer.of(m);