Open-source multiplayer game server compatible with the RuneScape client
https://www.openrs2.org/
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92 lines
3.6 KiB
92 lines
3.6 KiB
package dev.openrs2.deob.transform
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import com.github.michaelbull.logging.InlineLogger
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import dev.openrs2.asm.classpath.ClassPath
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import dev.openrs2.asm.classpath.Library
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import dev.openrs2.asm.transform.Transformer
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import org.objectweb.asm.Opcodes
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import org.objectweb.asm.tree.ClassNode
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import org.objectweb.asm.tree.MethodInsnNode
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import org.objectweb.asm.tree.MethodNode
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import javax.inject.Singleton
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/**
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* A [Transformer] that replaces `INVOKESPECIAL` instructions in static methods
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* with `INVOKEVIRTUAL` equivalents.
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*
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* The client contains some methods in `final` classes that use `INVOKESPECIAL`
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* to invoke non-`<init>` methods on objects of exactly the same type as the
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* containing class. Furthermore, these `INVOKESPECIAL` instructions are
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* sometimes present in `static` methods.
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*
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* As the containing class is `final` and as the method reference is not a
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* superclass of the containing class, these calls actually end up being
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* treated in the exact same way as an `INVOKEVIRTRUAL` call.
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*
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* While these calls are unusual (and probably never generated by a standard
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* Java compiler, as there is no way to express them in Java source code), they
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* are permitted by the
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* [JVM specification](https://docs.oracle.com/javase/specs/jvms/se11/html/jvms-6.html#jvms-6.5.invokespecial).
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*
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* It is likely that this unusual use of `INVOKESPECIAL` is an optimization
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* (`INVOKESPECIAL` was originally used as a more generic `INVOKENONVIRTUAL`
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* instruction, and non-virtual function calls are cheaper than virtual
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* function calls) or an obfuscation technique.
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*
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* The [StaticScramblingTransformer] moves static methods containing these
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* `INVOKESPECIAL` instructions to new classes. This change is still permitted
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* by the JVM specification, which does not place any restrictions on the class
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* referenced by the `INVOKESPECIAL` instruction.
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*
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* However, the
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* [verifier](https://github.com/openjdk/jdk11u/blob/3789983e89c9de252ef546a1b98a732a7d066650/src/java.base/share/native/libverify/check_code.c#L1342)
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* in modern JVMs is stricter and considers non-`<init>` `INVOKESPECIAL`
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* instructions referencing classes that are not the containing class or its
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* direct superclass illegal.
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*
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* This transformer replaces `INVOKESPECIAL` with equivalent `INVOKEVIRTUAL`
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* instructions where possible, allowing the [StaticScramblingTransformer] to
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* produce verifiable output.
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*/
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@Singleton
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class InvokeSpecialTransformer : Transformer() {
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private var invokeSpecialsReplaced = 0
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override fun preTransform(classPath: ClassPath) {
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invokeSpecialsReplaced = 0
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}
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override fun transformClass(classPath: ClassPath, library: Library, clazz: ClassNode): Boolean {
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require(clazz.access and (Opcodes.ACC_SUPER or Opcodes.ACC_INTERFACE) != 0)
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return false
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}
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override fun transformCode(classPath: ClassPath, library: Library, clazz: ClassNode, method: MethodNode): Boolean {
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if ((clazz.access and Opcodes.ACC_FINAL) == 0) {
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return false
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}
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for (insn in method.instructions) {
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if (insn !is MethodInsnNode || insn.opcode != Opcodes.INVOKESPECIAL) {
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continue
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} else if (insn.name == "<init>") {
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continue
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} else if (insn.owner != clazz.name) {
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continue
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}
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insn.opcode = Opcodes.INVOKEVIRTUAL
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invokeSpecialsReplaced++
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}
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return false
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}
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override fun postTransform(classPath: ClassPath) {
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logger.info { "Replaced $invokeSpecialsReplaced INVOKESPECIALs with INVOKEVIRTUAL" }
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}
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private companion object {
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private val logger = InlineLogger()
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}
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}
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