Paper/patches/server/0015-Deobfuscate-stacktraces-in-log-messages-crash-report.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jason Penilla <11360596+jpenilla@users.noreply.github.com>
Date: Sun, 20 Jun 2021 18:19:09 -0700
Subject: [PATCH] Deobfuscate stacktraces in log messages, crash reports, and
 etc.


diff --git a/build.gradle.kts b/build.gradle.kts
index b29cd3fba110261dfabb7b63c44ff850393a6480..79011b24207ec46872ba7196a4dd8d7a7c4ce848 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -34,6 +34,7 @@ dependencies {
     implementation("org.ow2.asm:asm-commons:9.7")
     implementation("org.spongepowered:configurate-yaml:4.2.0-SNAPSHOT") // Paper - config files
     implementation("commons-lang:commons-lang:2.6")
+    implementation("net.fabricmc:mapping-io:0.5.0") // Paper - needed to read mappings for stacktrace deobfuscation
     runtimeOnly("com.lmax:disruptor:3.4.4") // Paper
 
     runtimeOnly("org.apache.maven:maven-resolver-provider:3.9.6")
diff --git a/src/log4jPlugins/java/io/papermc/paper/logging/StacktraceDeobfuscatingRewritePolicy.java b/src/log4jPlugins/java/io/papermc/paper/logging/StacktraceDeobfuscatingRewritePolicy.java
new file mode 100644
index 0000000000000000000000000000000000000000..66b6011ee3684695b2ab9292961c80bf2a420ee9
--- /dev/null
+++ b/src/log4jPlugins/java/io/papermc/paper/logging/StacktraceDeobfuscatingRewritePolicy.java
@@ -0,0 +1,66 @@
+package io.papermc.paper.logging;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+import org.apache.logging.log4j.core.Core;
+import org.apache.logging.log4j.core.LogEvent;
+import org.apache.logging.log4j.core.appender.rewrite.RewritePolicy;
+import org.apache.logging.log4j.core.config.plugins.Plugin;
+import org.apache.logging.log4j.core.config.plugins.PluginFactory;
+import org.apache.logging.log4j.core.impl.Log4jLogEvent;
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+@Plugin(
+    name = "StacktraceDeobfuscatingRewritePolicy",
+    category = Core.CATEGORY_NAME,
+    elementType = "rewritePolicy",
+    printObject = true
+)
+public final class StacktraceDeobfuscatingRewritePolicy implements RewritePolicy {
+    private static final MethodHandle DEOBFUSCATE_THROWABLE;
+
+    static {
+        try {
+            final Class<?> cls = Class.forName("io.papermc.paper.util.StacktraceDeobfuscator");
+            final MethodHandles.Lookup lookup = MethodHandles.lookup();
+            final VarHandle instanceHandle = lookup.findStaticVarHandle(cls, "INSTANCE", cls);
+            final Object deobfuscator = instanceHandle.get();
+            DEOBFUSCATE_THROWABLE = lookup
+                .unreflect(cls.getDeclaredMethod("deobfuscateThrowable", Throwable.class))
+                .bindTo(deobfuscator);
+        } catch (final ReflectiveOperationException ex) {
+            throw new IllegalStateException(ex);
+        }
+    }
+
+    private StacktraceDeobfuscatingRewritePolicy() {
+    }
+
+    @Override
+    public @NonNull LogEvent rewrite(final @NonNull LogEvent rewrite) {
+        final Throwable thrown = rewrite.getThrown();
+        if (thrown != null) {
+            deobfuscateThrowable(thrown);
+            return new Log4jLogEvent.Builder(rewrite)
+                .setThrownProxy(null)
+                .build();
+        }
+        return rewrite;
+    }
+
+    private static void deobfuscateThrowable(final Throwable thrown) {
+        try {
+            DEOBFUSCATE_THROWABLE.invoke(thrown);
+        } catch (final Error e) {
+            throw e;
+        } catch (final Throwable e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @PluginFactory
+    public static @NonNull StacktraceDeobfuscatingRewritePolicy createPolicy() {
+        return new StacktraceDeobfuscatingRewritePolicy();
+    }
+}
diff --git a/src/main/java/io/papermc/paper/util/ObfHelper.java b/src/main/java/io/papermc/paper/util/ObfHelper.java
new file mode 100644
index 0000000000000000000000000000000000000000..e8ff684d8bd994c64ff34f20e1e0601b678244c1
--- /dev/null
+++ b/src/main/java/io/papermc/paper/util/ObfHelper.java
@@ -0,0 +1,147 @@
+package io.papermc.paper.util;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import net.fabricmc.mappingio.MappingReader;
+import net.fabricmc.mappingio.format.MappingFormat;
+import net.fabricmc.mappingio.tree.MappingTree;
+import net.fabricmc.mappingio.tree.MemoryMappingTree;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public enum ObfHelper {
+    INSTANCE;
+
+    public static final String MOJANG_PLUS_YARN_NAMESPACE = "mojang+yarn";
+    public static final String SPIGOT_NAMESPACE = "spigot";
+
+    private final @Nullable Map<String, ClassMapping> mappingsByObfName;
+    private final @Nullable Map<String, ClassMapping> mappingsByMojangName;
+
+    ObfHelper() {
+        final @Nullable Set<ClassMapping> maps = loadMappingsIfPresent();
+        if (maps != null) {
+            this.mappingsByObfName = maps.stream().collect(Collectors.toUnmodifiableMap(ClassMapping::obfName, map -> map));
+            this.mappingsByMojangName = maps.stream().collect(Collectors.toUnmodifiableMap(ClassMapping::mojangName, map -> map));
+        } else {
+            this.mappingsByObfName = null;
+            this.mappingsByMojangName = null;
+        }
+    }
+
+    public @Nullable Map<String, ClassMapping> mappingsByObfName() {
+        return this.mappingsByObfName;
+    }
+
+    public @Nullable Map<String, ClassMapping> mappingsByMojangName() {
+        return this.mappingsByMojangName;
+    }
+
+    /**
+     * Attempts to get the obf name for a given class by its Mojang name. Will
+     * return the input string if mappings are not present.
+     *
+     * @param fullyQualifiedMojangName fully qualified class name (dotted)
+     * @return mapped or original fully qualified (dotted) class name
+     */
+    public String reobfClassName(final String fullyQualifiedMojangName) {
+        if (this.mappingsByMojangName == null) {
+            return fullyQualifiedMojangName;
+        }
+
+        final ClassMapping map = this.mappingsByMojangName.get(fullyQualifiedMojangName);
+        if (map == null) {
+            return fullyQualifiedMojangName;
+        }
+
+        return map.obfName();
+    }
+
+    /**
+     * Attempts to get the Mojang name for a given class by its obf name. Will
+     * return the input string if mappings are not present.
+     *
+     * @param fullyQualifiedObfName fully qualified class name (dotted)
+     * @return mapped or original fully qualified (dotted) class name
+     */
+    public String deobfClassName(final String fullyQualifiedObfName) {
+        if (this.mappingsByObfName == null) {
+            return fullyQualifiedObfName;
+        }
+
+        final ClassMapping map = this.mappingsByObfName.get(fullyQualifiedObfName);
+        if (map == null) {
+            return fullyQualifiedObfName;
+        }
+
+        return map.mojangName();
+    }
+
+    private static @Nullable Set<ClassMapping> loadMappingsIfPresent() {
+        try (final @Nullable InputStream mappingsInputStream = ObfHelper.class.getClassLoader().getResourceAsStream("META-INF/mappings/reobf.tiny")) {
+            if (mappingsInputStream == null) {
+                return null;
+            }
+            final MemoryMappingTree tree = new MemoryMappingTree();
+            MappingReader.read(new InputStreamReader(mappingsInputStream, StandardCharsets.UTF_8), MappingFormat.TINY_2_FILE, tree);
+            final Set<ClassMapping> classes = new HashSet<>();
+
+            final StringPool pool = new StringPool();
+            for (final MappingTree.ClassMapping cls : tree.getClasses()) {
+                final Map<String, String> methods = new HashMap<>();
+
+                for (final MappingTree.MethodMapping methodMapping : cls.getMethods()) {
+                    methods.put(
+                        pool.string(methodKey(
+                            Objects.requireNonNull(methodMapping.getName(SPIGOT_NAMESPACE)),
+                            Objects.requireNonNull(methodMapping.getDesc(SPIGOT_NAMESPACE))
+                        )),
+                        pool.string(Objects.requireNonNull(methodMapping.getName(MOJANG_PLUS_YARN_NAMESPACE)))
+                    );
+                }
+
+                final ClassMapping map = new ClassMapping(
+                    Objects.requireNonNull(cls.getName(SPIGOT_NAMESPACE)).replace('/', '.'),
+                    Objects.requireNonNull(cls.getName(MOJANG_PLUS_YARN_NAMESPACE)).replace('/', '.'),
+                    Map.copyOf(methods)
+                );
+                classes.add(map);
+            }
+
+            return Set.copyOf(classes);
+        } catch (final IOException ex) {
+            System.err.println("Failed to load mappings for stacktrace deobfuscation.");
+            ex.printStackTrace();
+            return null;
+        }
+    }
+
+    public static String methodKey(final String obfName, final String obfDescriptor) {
+        return obfName + obfDescriptor;
+    }
+
+    private static final class StringPool {
+        private final Map<String, String> pool = new HashMap<>();
+
+        public String string(final String string) {
+            return this.pool.computeIfAbsent(string, Function.identity());
+        }
+    }
+
+    public record ClassMapping(
+        String obfName,
+        String mojangName,
+        Map<String, String> methodsByObf
+    ) {}
+}
diff --git a/src/main/java/io/papermc/paper/util/StacktraceDeobfuscator.java b/src/main/java/io/papermc/paper/util/StacktraceDeobfuscator.java
new file mode 100644
index 0000000000000000000000000000000000000000..eb910d4abf91488fa7cf1f5d47e0ee916c47f512
--- /dev/null
+++ b/src/main/java/io/papermc/paper/util/StacktraceDeobfuscator.java
@@ -0,0 +1,163 @@
+package io.papermc.paper.util;
+
+import io.papermc.paper.configuration.GlobalConfiguration;
+import it.unimi.dsi.fastutil.ints.IntArrayList;
+import it.unimi.dsi.fastutil.ints.IntList;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.framework.qual.DefaultQualifier;
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.Label;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.Opcodes;
+
+@DefaultQualifier(NonNull.class)
+public enum StacktraceDeobfuscator {
+    INSTANCE;
+
+    private final Map<Class<?>, Map<String, IntList>> lineMapCache = Collections.synchronizedMap(new LinkedHashMap<>(128, 0.75f, true) {
+        @Override
+        protected boolean removeEldestEntry(final Map.Entry<Class<?>, Map<String, IntList>> eldest) {
+            return this.size() > 127;
+        }
+    });
+
+    public void deobfuscateThrowable(final Throwable throwable) {
+        if (GlobalConfiguration.get() != null && !GlobalConfiguration.get().logging.deobfuscateStacktraces) { // handle null as true
+            return;
+        }
+
+        throwable.setStackTrace(this.deobfuscateStacktrace(throwable.getStackTrace()));
+        final Throwable cause = throwable.getCause();
+        if (cause != null) {
+            this.deobfuscateThrowable(cause);
+        }
+        for (final Throwable suppressed : throwable.getSuppressed()) {
+            this.deobfuscateThrowable(suppressed);
+        }
+    }
+
+    public StackTraceElement[] deobfuscateStacktrace(final StackTraceElement[] traceElements) {
+        if (GlobalConfiguration.get() != null && !GlobalConfiguration.get().logging.deobfuscateStacktraces) { // handle null as true
+            return traceElements;
+        }
+
+        final @Nullable Map<String, ObfHelper.ClassMapping> mappings = ObfHelper.INSTANCE.mappingsByObfName();
+        if (mappings == null || traceElements.length == 0) {
+            return traceElements;
+        }
+        final StackTraceElement[] result = new StackTraceElement[traceElements.length];
+        for (int i = 0; i < traceElements.length; i++) {
+            final StackTraceElement element = traceElements[i];
+
+            final String className = element.getClassName();
+            final String methodName = element.getMethodName();
+
+            final ObfHelper.ClassMapping classMapping = mappings.get(className);
+            if (classMapping == null) {
+                result[i] = element;
+                continue;
+            }
+
+            final Class<?> clazz;
+            try {
+                clazz = Class.forName(className);
+            } catch (final ClassNotFoundException ex) {
+                throw new RuntimeException(ex);
+            }
+            final @Nullable String methodKey = this.determineMethodForLine(clazz, element.getLineNumber());
+            final @Nullable String mappedMethodName = methodKey == null ? null : classMapping.methodsByObf().get(methodKey);
+
+            result[i] = new StackTraceElement(
+                element.getClassLoaderName(),
+                element.getModuleName(),
+                element.getModuleVersion(),
+                classMapping.mojangName(),
+                mappedMethodName != null ? mappedMethodName : methodName,
+                sourceFileName(classMapping.mojangName()),
+                element.getLineNumber()
+            );
+        }
+        return result;
+    }
+
+    private @Nullable String determineMethodForLine(final Class<?> clazz, final int lineNumber) {
+        final Map<String, IntList> lineMap = this.lineMapCache.computeIfAbsent(clazz, StacktraceDeobfuscator::buildLineMap);
+        for (final var entry : lineMap.entrySet()) {
+            final String methodKey = entry.getKey();
+            final IntList lines = entry.getValue();
+            for (int i = 0, linesSize = lines.size(); i < linesSize; i++) {
+                final int num = lines.getInt(i);
+                if (num == lineNumber) {
+                    return methodKey;
+                }
+            }
+        }
+        return null;
+    }
+
+    private static String sourceFileName(final String fullClassName) {
+        final int dot = fullClassName.lastIndexOf('.');
+        final String className = dot == -1
+            ? fullClassName
+            : fullClassName.substring(dot + 1);
+        final String rootClassName = className.split("\\$")[0];
+        return rootClassName + ".java";
+    }
+
+    private static Map<String, IntList> buildLineMap(final Class<?> key) {
+        final Map<String, IntList> lineMap = new HashMap<>();
+        final class LineCollectingMethodVisitor extends MethodVisitor {
+            private final IntList lines = new IntArrayList();
+            private final String name;
+            private final String descriptor;
+
+            LineCollectingMethodVisitor(String name, String descriptor) {
+                super(Opcodes.ASM9);
+                this.name = name;
+                this.descriptor = descriptor;
+            }
+
+            @Override
+            public void visitLineNumber(int line, Label start) {
+                super.visitLineNumber(line, start);
+                this.lines.add(line);
+            }
+
+            @Override
+            public void visitEnd() {
+                super.visitEnd();
+                lineMap.put(ObfHelper.methodKey(this.name, this.descriptor), this.lines);
+            }
+        }
+        final ClassVisitor classVisitor = new ClassVisitor(Opcodes.ASM9) {
+            @Override
+            public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
+                return new LineCollectingMethodVisitor(name, descriptor);
+            }
+        };
+        try {
+            final @Nullable InputStream inputStream = StacktraceDeobfuscator.class.getClassLoader()
+                .getResourceAsStream(key.getName().replace('.', '/') + ".class");
+            if (inputStream == null) {
+                throw new IllegalStateException("Could not find class file: " + key.getName());
+            }
+            final byte[] classData;
+            try (inputStream) {
+                classData = inputStream.readAllBytes();
+            }
+            final ClassReader reader = new ClassReader(classData);
+            reader.accept(classVisitor, 0);
+        } catch (final IOException ex) {
+            throw new RuntimeException(ex);
+        }
+        return lineMap;
+    }
+}
diff --git a/src/main/java/net/minecraft/CrashReport.java b/src/main/java/net/minecraft/CrashReport.java
index a23407fa1b906743890cff74f5051ad55d59c85e..06c514b2d0674cd7df6692981f020437ea0f2f91 100644
--- a/src/main/java/net/minecraft/CrashReport.java
+++ b/src/main/java/net/minecraft/CrashReport.java
@@ -34,6 +34,7 @@ public class CrashReport {
     private final SystemReport systemReport = new SystemReport();
 
     public CrashReport(String message, Throwable cause) {
+        io.papermc.paper.util.StacktraceDeobfuscator.INSTANCE.deobfuscateThrowable(cause); // Paper
         this.title = message;
         this.exception = cause;
         this.systemReport.setDetail("CraftBukkit Information", new org.bukkit.craftbukkit.CraftCrashReport()); // CraftBukkit
diff --git a/src/main/java/net/minecraft/CrashReportCategory.java b/src/main/java/net/minecraft/CrashReportCategory.java
index f367ba058018074bfe6e4fe88bcc875ea9794d9e..2176171954609fd88f97f93408e14e018c1d6eaa 100644
--- a/src/main/java/net/minecraft/CrashReportCategory.java
+++ b/src/main/java/net/minecraft/CrashReportCategory.java
@@ -110,6 +110,7 @@ public class CrashReportCategory {
         } else {
             this.stackTrace = new StackTraceElement[stackTraceElements.length - 3 - ignoredCallCount];
             System.arraycopy(stackTraceElements, 3 + ignoredCallCount, this.stackTrace, 0, this.stackTrace.length);
+            this.stackTrace = io.papermc.paper.util.StacktraceDeobfuscator.INSTANCE.deobfuscateStacktrace(this.stackTrace); // Paper
             return this.stackTrace.length;
         }
     }
diff --git a/src/main/java/net/minecraft/network/Connection.java b/src/main/java/net/minecraft/network/Connection.java
index 256a983c7345902600d52d7b7e3056162275f4c7..0ccfdceea8e211c595be2dad2392876109b4eeef 100644
--- a/src/main/java/net/minecraft/network/Connection.java
+++ b/src/main/java/net/minecraft/network/Connection.java
@@ -82,13 +82,13 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
         marker.add(Connection.PACKET_MARKER);
     });
     public static final Supplier<NioEventLoopGroup> NETWORK_WORKER_GROUP = Suppliers.memoize(() -> {
-        return new NioEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Client IO #%d").setDaemon(true).build());
+        return new NioEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Client IO #%d").setDaemon(true).setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(LOGGER)).build()); // Paper
     });
     public static final Supplier<EpollEventLoopGroup> NETWORK_EPOLL_WORKER_GROUP = Suppliers.memoize(() -> {
-        return new EpollEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Epoll Client IO #%d").setDaemon(true).build());
+        return new EpollEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Epoll Client IO #%d").setDaemon(true).setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(LOGGER)).build()); // Paper
     });
     public static final Supplier<DefaultEventLoopGroup> LOCAL_WORKER_GROUP = Suppliers.memoize(() -> {
-        return new DefaultEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Local Client IO #%d").setDaemon(true).build());
+        return new DefaultEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Local Client IO #%d").setDaemon(true).setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(LOGGER)).build()); // Paper
     });
     private static final ProtocolInfo<ServerHandshakePacketListener> INITIAL_PROTOCOL = HandshakeProtocols.SERVERBOUND;
     private final PacketFlow receiving;
@@ -189,7 +189,7 @@ public class Connection extends SimpleChannelInboundHandler<Packet<?>> {
 
             }
         }
-        if (net.minecraft.server.MinecraftServer.getServer().isDebugging()) throwable.printStackTrace(); // Spigot
+        if (net.minecraft.server.MinecraftServer.getServer().isDebugging()) io.papermc.paper.util.TraceUtil.printStackTrace(throwable); // Spigot // Paper
     }
 
     protected void channelRead0(ChannelHandlerContext channelhandlercontext, Packet<?> packet) {
diff --git a/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java b/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
index 9249122da7282929f87613f41984b8085d7b53ec..21b8f1913ff54d2b1553826269355da8bdb7f702 100644
--- a/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
+++ b/src/main/java/net/minecraft/server/dedicated/DedicatedServer.java
@@ -206,6 +206,7 @@ public class DedicatedServer extends MinecraftServer implements ServerInterface
         org.spigotmc.SpigotConfig.init((java.io.File) this.options.valueOf("spigot-settings"));
         org.spigotmc.SpigotConfig.registerCommands();
         // Spigot end
+        io.papermc.paper.util.ObfHelper.INSTANCE.getClass(); // Paper - load mappings for stacktrace deobf and etc.
         // Paper start - initialize global and world-defaults configuration
         this.paperConfigurations.initializeGlobalConfiguration(this.registryAccess());
         this.paperConfigurations.initializeWorldDefaultsConfiguration(this.registryAccess());
diff --git a/src/main/java/net/minecraft/server/network/ServerConnectionListener.java b/src/main/java/net/minecraft/server/network/ServerConnectionListener.java
index 987360a266a5a870f06929b00c9f451901188fd6..2cf3e79ec5e8706b71d27ebad4668773f0b91195 100644
--- a/src/main/java/net/minecraft/server/network/ServerConnectionListener.java
+++ b/src/main/java/net/minecraft/server/network/ServerConnectionListener.java
@@ -52,10 +52,10 @@ public class ServerConnectionListener {
 
     private static final Logger LOGGER = LogUtils.getLogger();
     public static final Supplier<NioEventLoopGroup> SERVER_EVENT_GROUP = Suppliers.memoize(() -> {
-        return new NioEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Server IO #%d").setDaemon(true).build());
+        return new NioEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Server IO #%d").setDaemon(true).setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(LOGGER)).build()); // Paper
     });
     public static final Supplier<EpollEventLoopGroup> SERVER_EPOLL_EVENT_GROUP = Suppliers.memoize(() -> {
-        return new EpollEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Epoll Server IO #%d").setDaemon(true).build());
+        return new EpollEventLoopGroup(0, (new ThreadFactoryBuilder()).setNameFormat("Netty Epoll Server IO #%d").setDaemon(true).setUncaughtExceptionHandler(new net.minecraft.DefaultUncaughtExceptionHandlerWithName(LOGGER)).build()); // Paper
     });
     final MinecraftServer server;
     public volatile boolean running;
diff --git a/src/main/java/net/minecraft/server/players/OldUsersConverter.java b/src/main/java/net/minecraft/server/players/OldUsersConverter.java
index 8d06e8d286da2573e40794adab695ff77e5afd86..68551947f5b7d3471f15bd74ccd86519ab34c1c1 100644
--- a/src/main/java/net/minecraft/server/players/OldUsersConverter.java
+++ b/src/main/java/net/minecraft/server/players/OldUsersConverter.java
@@ -356,7 +356,7 @@ public class OldUsersConverter {
                         try {
                             root = NbtIo.readCompressed(new java.io.FileInputStream(file5), NbtAccounter.unlimitedHeap());
                         } catch (Exception exception) {
-                            exception.printStackTrace();
+                            io.papermc.paper.util.TraceUtil.printStackTrace(exception); // Paper
                         }
 
                         if (root != null) {
@@ -369,7 +369,7 @@ public class OldUsersConverter {
                             try {
                                 NbtIo.writeCompressed(root, new java.io.FileOutputStream(file2));
                             } catch (Exception exception) {
-                                exception.printStackTrace();
+                                io.papermc.paper.util.TraceUtil.printStackTrace(exception); // Paper
                             }
                        }
                         // CraftBukkit end
diff --git a/src/main/java/org/spigotmc/WatchdogThread.java b/src/main/java/org/spigotmc/WatchdogThread.java
index c4bf7053d83d207caca0e13e19f5c1afa7062de3..f697d45e0ac4e9cdc8a46121510a04c0f294d91f 100644
--- a/src/main/java/org/spigotmc/WatchdogThread.java
+++ b/src/main/java/org/spigotmc/WatchdogThread.java
@@ -130,7 +130,7 @@ public class WatchdogThread extends Thread
         }
         log.log( Level.SEVERE, "\tStack:" );
         //
-        for ( StackTraceElement stack : thread.getStackTrace() )
+        for ( StackTraceElement stack : io.papermc.paper.util.StacktraceDeobfuscator.INSTANCE.deobfuscateStacktrace(thread.getStackTrace()) ) // Paper
         {
             log.log( Level.SEVERE, "\t\t" + stack );
         }
diff --git a/src/main/resources/log4j2.xml b/src/main/resources/log4j2.xml
index 18e961a37b2830da6e5dab7aa35116b2f5215898..128fa1376f22d3429a23d79a2772abf2e7fec2bc 100644
--- a/src/main/resources/log4j2.xml
+++ b/src/main/resources/log4j2.xml
@@ -30,10 +30,14 @@
             <DefaultRolloverStrategy max="1000"/>
         </RollingRandomAccessFile>
         <Async name="Async">
+            <AppenderRef ref="rewrite"/>
+        </Async>
+        <Rewrite name="rewrite">
+            <StacktraceDeobfuscatingRewritePolicy />
             <AppenderRef ref="File"/>
             <AppenderRef ref="TerminalConsole" level="info"/>
             <AppenderRef ref="ServerGuiConsole" level="info"/>
-        </Async>
+        </Rewrite>
     </Appenders>
     <Loggers>
         <Root level="info">