tree 5056001e02d8c4494b643c8d53fd32621e127c1c
parent abdb4592fa28d6e75f1160f01cde58ad7c3fef37
author Alex Light <allight@google.com> 1558371884 -0700
committer Treehugger Robot <treehugger-gerrit@google.com> 1558484978 +0000

Add verifier fallback for JVMTI Get/SetLocalVariable

The JVMTI Get/SetLocalVariable functions used to rely entirely on the
Dex DebugInfo to determine the types of each of the registers. This
could lead to problems since, to prevent possible stack corruption, we
would not allow stack modification if the data was not present.

In order to remove this restriction we will instead make use of the
method verifier to ensure the modification is sensible when the
DebugInfo is not present. Since reconstructing this information using
the verifier is quite slow (compared to reading it from a table) we
will only do this when the table is missing.

Since the verifier lacks some of the information available when
creating the DebugLocalInfo table some semantics will change depending
on if the table is present or not.

 - When the DebugLocalInfo table is not present we cannot always
   distinguish between floats, ints, and other single-register
   primitive types. For simplicity all single-register primitive
   types can be modified and read by both the Float and Int versions
   of the local variable functions.

 - Similarly we cannot always distinguish between long and double
   variables.

 - Reference types are checked against what the verifier thinks they
   need to be according to type unification. This might be more or
   less specific than the types recorded in the functions source code.

 - Constant int/float '0' values and 'null' cannot always be
   differentiated by the verifier. Therefore, one may not always be
   able to modify some null or constant 0 registers.

Test: ./test.py --host
Bug: 131711256

Change-Id: I1c9d857ccdec752bfd4ebad76cc9ad96e143866c