From a869d47d1112aaa7593ff05f61f607389481cb98 Mon Sep 17 00:00:00 2001
From: Major <major@emulate.rs>
Date: Sun, 8 Mar 2020 06:31:15 +0000
Subject: [PATCH] Add Fernflower Exception transformer

Fernflower fails to decompile any exception handler with an end_pc
(`to` in Fernflower nomenclature) equal to the length of the code array,
even though this is permitted in the class file spec. This transformer
inserts a NOP at the end of any code array that has such an exception
handler.

Signed-off-by: Major <major@emulate.rs>
---
 .../java/dev/openrs2/deob/Deobfuscator.kt     |  4 ++-
 .../FernflowerExceptionTransformer.kt         | 36 +++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 deob/src/main/java/dev/openrs2/deob/transform/FernflowerExceptionTransformer.kt

diff --git a/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt b/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt
index c220fab447..6fef1941f4 100644
--- a/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt
+++ b/deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt
@@ -18,6 +18,7 @@ import dev.openrs2.deob.transform.DummyArgTransformer
 import dev.openrs2.deob.transform.DummyLocalTransformer
 import dev.openrs2.deob.transform.EmptyClassTransformer
 import dev.openrs2.deob.transform.ExceptionTracingTransformer
+import dev.openrs2.deob.transform.FernflowerExceptionTransformer
 import dev.openrs2.deob.transform.FieldOrderTransformer
 import dev.openrs2.deob.transform.FinalTransformer
 import dev.openrs2.deob.transform.InvokeSpecialTransformer
@@ -177,7 +178,8 @@ class Deobfuscator(private val input: Path, private val output: Path) {
             MethodOrderTransformer(),
             VisibilityTransformer(),
             OverrideTransformer(),
-            OriginalPcRestoreTransformer()
+            OriginalPcRestoreTransformer(),
+            FernflowerExceptionTransformer()
         )
     }
 }
diff --git a/deob/src/main/java/dev/openrs2/deob/transform/FernflowerExceptionTransformer.kt b/deob/src/main/java/dev/openrs2/deob/transform/FernflowerExceptionTransformer.kt
new file mode 100644
index 0000000000..ba09cc261c
--- /dev/null
+++ b/deob/src/main/java/dev/openrs2/deob/transform/FernflowerExceptionTransformer.kt
@@ -0,0 +1,36 @@
+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.nextReal
+import dev.openrs2.asm.transform.Transformer
+import org.objectweb.asm.Opcodes
+import org.objectweb.asm.tree.ClassNode
+import org.objectweb.asm.tree.InsnNode
+import org.objectweb.asm.tree.MethodNode
+
+class FernflowerExceptionTransformer : Transformer() {
+    private var nopsInserted = 0
+
+    override fun preTransform(classPath: ClassPath) {
+        nopsInserted = 0
+    }
+
+    override fun transformCode(classPath: ClassPath, library: Library, clazz: ClassNode, method: MethodNode): Boolean {
+        if (method.tryCatchBlocks.any { it.end.nextReal == null }) {
+            method.instructions.add(InsnNode(Opcodes.NOP))
+            nopsInserted++
+        }
+
+        return false
+    }
+
+    override fun postTransform(classPath: ClassPath) {
+        logger.info { "Inserted $nopsInserted NOPs to correct Fernflower's exception generation" }
+    }
+
+    private companion object {
+        private val logger = InlineLogger()
+    }
+}