Convert Java 1.1-style synchronized blocks to a more modern style

The non-HD client appears to have been compiled with javac 1.1 or 1.2,
which compiles synchronized blocks differently to modern versions of
Java. For example, it uses a single try/catch block (modern versions use
two, the latter of which is recursive), subroutines (modern versions do
not) and the range of the try block is narrower.

Fernflower doesn't understand this old style of bytecode, and produces
empty synchronized blocks that do not cover the correct range.

The MONITORENTER sequence is also slightly different: it uses
ASTORE ALOAD MONITORENTER after pushing the monitor variable, rather
than DUP ASTORE MONITORENTER. This doesn't break Fernflower, but does
make it introduce a pointless assignment to a variable only used in the
synchronized() statement, rather than inlining the expression.

This commit introduces a transformer which fixes up Java 1.1-style
synchronized blocks just enough for Fernflower to be able to decompile
them cleanly. (It doesn't add a recursive try/catch, as Fernflower
ignores them.)

Signed-off-by: Graham <gpe@openrs2.dev>
bzip2
Graham 5 years ago
parent 3b73358183
commit 2862b305c5
  1. 2
      deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt
  2. 115
      deob/src/main/java/dev/openrs2/deob/transform/MonitorTransformer.kt

@ -23,6 +23,7 @@ import dev.openrs2.deob.transform.FieldOrderTransformer
import dev.openrs2.deob.transform.FinalTransformer import dev.openrs2.deob.transform.FinalTransformer
import dev.openrs2.deob.transform.InvokeSpecialTransformer import dev.openrs2.deob.transform.InvokeSpecialTransformer
import dev.openrs2.deob.transform.MethodOrderTransformer import dev.openrs2.deob.transform.MethodOrderTransformer
import dev.openrs2.deob.transform.MonitorTransformer
import dev.openrs2.deob.transform.OpaquePredicateTransformer import dev.openrs2.deob.transform.OpaquePredicateTransformer
import dev.openrs2.deob.transform.OriginalNameTransformer import dev.openrs2.deob.transform.OriginalNameTransformer
import dev.openrs2.deob.transform.OriginalPcRestoreTransformer import dev.openrs2.deob.transform.OriginalPcRestoreTransformer
@ -154,6 +155,7 @@ class Deobfuscator(private val input: Path, private val output: Path) {
ResourceTransformer(), ResourceTransformer(),
OpaquePredicateTransformer(), OpaquePredicateTransformer(),
ExceptionTracingTransformer(), ExceptionTracingTransformer(),
MonitorTransformer(),
BitShiftTransformer(), BitShiftTransformer(),
CanvasTransformer(), CanvasTransformer(),
FieldOrderTransformer(), FieldOrderTransformer(),

@ -0,0 +1,115 @@
package dev.openrs2.deob.transform
import com.github.michaelbull.logging.InlineLogger
import dev.openrs2.asm.InsnMatcher
import dev.openrs2.asm.classpath.ClassPath
import dev.openrs2.asm.classpath.Library
import dev.openrs2.asm.nextReal
import dev.openrs2.asm.previousReal
import dev.openrs2.asm.transform.Transformer
import org.objectweb.asm.Opcodes
import org.objectweb.asm.tree.AbstractInsnNode
import org.objectweb.asm.tree.ClassNode
import org.objectweb.asm.tree.InsnNode
import org.objectweb.asm.tree.JumpInsnNode
import org.objectweb.asm.tree.LabelNode
import org.objectweb.asm.tree.MethodNode
class MonitorTransformer : Transformer() {
private var subroutinesInlined = 0
private var tryRangesExtended = 0
private var loadsReplaced = 0
override fun preTransform(classPath: ClassPath) {
subroutinesInlined = 0
tryRangesExtended = 0
loadsReplaced = 0
}
override fun transformCode(classPath: ClassPath, library: Library, clazz: ClassNode, method: MethodNode): Boolean {
inlineSubroutines(method)
extendTryRanges(method)
replaceLoadWithDup(method)
return false
}
private fun inlineSubroutines(method: MethodNode) {
val subroutines = mutableMapOf<AbstractInsnNode, List<AbstractInsnNode>>()
for (match in SUBROUTINE_MATCHER.match(method.instructions)) {
subroutines[match[0]] = match
}
for (match in JSR_MATCHER.match(method.instructions)) {
val jsr = match[1] as JumpInsnNode
val subroutine = subroutines[jsr.label.nextReal] ?: continue
val ret = subroutine[3] as JumpInsnNode
if (ret.label.nextReal != jsr.nextReal) {
continue
}
val clonedLabels = emptyMap<LabelNode, LabelNode>()
method.instructions.set(match[0], subroutine[1].clone(clonedLabels))
method.instructions.set(match[1], subroutine[2].clone(clonedLabels))
subroutinesInlined++
}
}
private fun extendTryRanges(method: MethodNode) {
for (tryCatch in method.tryCatchBlocks) {
if (tryCatch.type != null) {
continue
}
val monitorenter = tryCatch.start.previousReal ?: continue
if (monitorenter.opcode != Opcodes.MONITORENTER) {
continue
}
// extend the try to cover the ALOAD and MONTITOREXIT instructions
val aload = tryCatch.end.nextReal ?: continue
if (aload.opcode != Opcodes.ALOAD) {
continue
}
val monitorexit = aload.nextReal ?: continue
if (monitorexit.opcode != Opcodes.MONITOREXIT) {
continue
}
val end = monitorexit.nextReal ?: continue
val label = LabelNode()
method.instructions.insertBefore(end, label)
tryCatch.end = label
tryRangesExtended++
}
}
private fun replaceLoadWithDup(method: MethodNode) {
for (match in LOAD_MATCHER.match(method.instructions)) {
method.instructions.insertBefore(match[0], InsnNode(Opcodes.DUP))
method.instructions.remove(match[1])
loadsReplaced++
}
}
override fun postTransform(classPath: ClassPath) {
logger.info { "Inlined $subroutinesInlined MONITOREXIT subroutines" }
logger.info { "Extended $tryRangesExtended try ranges to cover MONITOREXIT instructions" }
logger.info { "Replaced $loadsReplaced ASTORE ALOAD sequences with DUP ASTORE" }
}
companion object {
private val logger = InlineLogger()
// these regexes rely on JSRInlinerAdapter running first
private val JSR_MATCHER = InsnMatcher.compile("ACONST_NULL GOTO")
private val SUBROUTINE_MATCHER = InsnMatcher.compile("ASTORE ALOAD MONITOREXIT GOTO")
private val LOAD_MATCHER = InsnMatcher.compile("ASTORE ALOAD MONITORENTER")
}
}
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