Byte code generated by XSLTC contains backwards branch when uninitialized
object is on stack
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Key: XALANJ-2146
URL: http://issues.apache.org/jira/browse/XALANJ-2146
Project: XalanJ2
Type: Bug
Components: XSLTC
Versions: CurrentCVS
Reporter: Henry Zongaro
Assigned to: Henry Zongaro
Priority: Critical
Fix For: 2.7.0-future-release
Section 4.3.4 of the Java Virtual Machine Specification, 2nd Edition, places
the following restriction on Java byte code:
«A valid instruction sequence must not have an uninitialized object on the
operand stack or in a local variable during a backwards branch, or in a local
variable in code protected by an exception handler or a finally clause.
Otherwise, a devious piece of code might fool the verifier into thinking it had
initialized a class instance when it had, in fact, initialized a class instance
created in a previous pass through a loop.»
There are a number of places where XSLTC generates code that violates this
requirement; a strict implementation of the verification process described by
the JVM specification would detect the invalid byte code. Most popular JVMs do
not seem to detect this problem - presumably because their verification is less
stringent - but this is a problem that needs to be fixed.
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