From ccb37f120b0b26e7b4dc38745efdd84f52966ba4 Mon Sep 17 00:00:00 2001
From: Graham <gpe@openrs2.dev>
Date: Sat, 29 Feb 2020 22:23:11 +0000
Subject: [PATCH] Add INVOKESPECIAL transformer

The obfuscator (or compiler, potentially?) converts INVOKEVIRTUAL
instructions to INVOKESPECIAL in the following circumstances:

 * The owner of the method is the same as the class containing the
   INVOKE instruction.
 * The owner's ACC_FINAL flag is set.

When those two conditions are met, and when ACC_SUPER is set on the
owner (which is always true in the RuneScape client, and the flag is
ignored in modern JVMs), then INVOKESPECIAL and INVOKEVIRTUAL are
equivalent.

This has not caused problems until now. However, the future static
scrambling transformer will break the first condition in some cases, as
it moves methods between classes.

This transformer reverses the obfuscation, such that INVOKEVIRTUAL is
used again. INVOKEVIRTUAL instructions may be moved between classes
without complication.
---
 .../java/dev/openrs2/deob/Deobfuscator.kt     |  2 +
 .../transform/InvokeSpecialTransformer.kt     | 48 +++++++++++++++++++
 2 files changed, 50 insertions(+)
 create mode 100644 deob/src/main/java/dev/openrs2/deob/transform/InvokeSpecialTransformer.kt

diff --git a/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt b/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt
index 9e4a477e..a0549280 100644
--- a/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt
+++ b/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt
@@ -19,6 +19,7 @@ import dev.openrs2.deob.transform.DummyLocalTransformer
 import dev.openrs2.deob.transform.ExceptionTracingTransformer
 import dev.openrs2.deob.transform.FieldOrderTransformer
 import dev.openrs2.deob.transform.FinalTransformer
+import dev.openrs2.deob.transform.InvokeSpecialTransformer
 import dev.openrs2.deob.transform.OpaquePredicateTransformer
 import dev.openrs2.deob.transform.OriginalNameTransformer
 import dev.openrs2.deob.transform.OverrideTransformer
@@ -164,6 +165,7 @@ class Deobfuscator(private val input: Path, private val output: Path) {
             ResetTransformer(),
             FinalTransformer(),
             ClassLiteralTransformer(),
+            InvokeSpecialTransformer(),
             VisibilityTransformer(),
             OverrideTransformer()
         )
diff --git a/deob/src/main/java/dev/openrs2/deob/transform/InvokeSpecialTransformer.kt b/deob/src/main/java/dev/openrs2/deob/transform/InvokeSpecialTransformer.kt
new file mode 100644
index 00000000..3d7bc150
--- /dev/null
+++ b/deob/src/main/java/dev/openrs2/deob/transform/InvokeSpecialTransformer.kt
@@ -0,0 +1,48 @@
+package dev.openrs2.deob.transform
+
+import com.github.michaelbull.logging.InlineLogger
+import dev.openrs2.asm.classpath.ClassPath
+import dev.openrs2.asm.classpath.Library
+import dev.openrs2.asm.transform.Transformer
+import org.objectweb.asm.Opcodes
+import org.objectweb.asm.tree.ClassNode
+import org.objectweb.asm.tree.MethodInsnNode
+import org.objectweb.asm.tree.MethodNode
+
+class InvokeSpecialTransformer : Transformer() {
+    private var invokeSpecialsReplaced = 0
+
+    override fun preTransform(classPath: ClassPath) {
+        invokeSpecialsReplaced = 0
+    }
+
+    override fun transformCode(classPath: ClassPath, library: Library, clazz: ClassNode, method: MethodNode): Boolean {
+        for (insn in method.instructions) {
+            if (insn !is MethodInsnNode || insn.opcode != Opcodes.INVOKESPECIAL) {
+                continue
+            } else if (insn.name == "<init>") {
+                continue
+            } else if (insn.owner != clazz.name) {
+                continue
+            }
+
+            val owner = classPath.getNode(insn.owner)!!
+            if ((owner.access and Opcodes.ACC_FINAL) == 0) {
+                continue
+            }
+
+            insn.opcode = Opcodes.INVOKEVIRTUAL
+            invokeSpecialsReplaced++
+        }
+
+        return false
+    }
+
+    override fun postTransform(classPath: ClassPath) {
+        logger.info { "Replaced $invokeSpecialsReplaced INVOKESPECIALs with INVOKEVIRTUAL" }
+    }
+
+    companion object {
+        private val logger = InlineLogger()
+    }
+}