Basic HTML version of Foils prepared August 4 1997

Foil 31 Byte Code Verification

From Remarks on Java and Internet Security Web Certificate CPS616 Enhancement -- Summer 1997 . by Geoffrey C. Fox


1 First one checks that .class file has correct format
2 Checks all that can be done without looking at byte codes
  • this includes superclass checking, verification of constant pool, and legal names and types for field and method references, final classes cannot be subclassed or overwritten
3 Then one looks at the byte code and checks that as executed it will give finite size stacks, correct typing for registers, fields and methods
4 One does not download the byte codes of required classes. However one does check that the class is used consistently with its definition
5 Some steps are for run time efficiency such as checking for some run time exceptions can be done at verification stage and removed in running code.

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