Bootstrap Classloader

CMakeLists.txt

@@ -9,7 +9,8 @@ project(SchokoVM)
 set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED True)
 
-find_package(Java 1.8 REQUIRED)
+find_package(Java 11 EXACT REQUIRED COMPONENTS Runtime Development)
+find_package(JNI 11 EXACT REQUIRED)
 include(UseJava)
 
 find_package(libzip)
@@ -102,6 +103,31 @@ else ()
     target_link_libraries(SchokoVM zip)
 endif ()
 
+
+#
+# OpenJDK
+#
+
+file(REAL_PATH ${Java_JAVAC_EXECUTABLE} JDK_HOME)
+get_filename_component(JDK_HOME ${JDK_HOME} DIRECTORY)
+get_filename_component(JDK_HOME ${JDK_HOME} DIRECTORY)
+message(STATUS "jdk: ${JDK_HOME}")
+
+set(JDK_BIN ${CMAKE_CURRENT_SOURCE_DIR}/jdk/bin)
+if(NOT IS_DIRECTORY ${JDK_BIN})
+    message(STATUS "Copying ${JDK_HOME} to ${JDK_BIN}")
+#    file(COPY ${JDK_HOME} DESTINATION ${JDK_BIN})
+    # this renames the target folder:
+    execute_process(COMMAND cp -r "${JDK_HOME}" "${JDK_BIN}")
+endif()
+
+set(JDK_EXPLODED ${CMAKE_CURRENT_SOURCE_DIR}/jdk/exploded-modules)
+if(NOT IS_DIRECTORY ${JDK_EXPLODED})
+    message(STATUS "Exploding")
+    execute_process(COMMAND ${JDK_HOME}/bin/jimage extract --dir "${JDK_EXPLODED}" "${JDK_BIN}/lib/modules")
+endif()
+
+
 #
 # Tests
 #

README.md

@@ -4,6 +4,10 @@ A Java Bytecode interpreter.
 
 [![Run tests](https://github.com/RobertObkircher/SchokoVM/actions/workflows/tests.yml/badge.svg)](https://github.com/RobertObkircher/SchokoVM/actions/workflows/tests.yml)
 
+# OpenJDK
+
+You need to download an OpenJDK release and the sources: `cd jdk && ./download.sh`
+
 # GDB
 
 You need a ~/.gdbinit in your home directory or the project .gdbinit file will be ignored:

jdk/.gitignore

@@ -0,0 +1,3 @@
+/bin/
+/exploded-modules/
+/jdk/

jdk/cleanup.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+set -e
+
+# clion doesn't want to delete the symlinks
+rm -rf bin
+rm -rf exploded-modules

jdk/download.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+set -e
+
+if [ -d "jdk" ]; then
+  echo "Skipping download of jdk sources"
+else
+  git clone https://github.com/openjdk/jdk.git
+  pushd jdk
+  git checkout -b SchokoVM jdk-11+9
+  popd
+fi
+
+

src/classfile.hpp

@@ -782,7 +782,9 @@ struct ClassFile {
     u2 access_flags;
     CONSTANT_Class_info *this_class;
     // nullptr for class Object
-    CONSTANT_Class_info *super_class;
+    CONSTANT_Class_info *super_class_ref;
+    // nullptr for class Object and before resolution
+    ClassFile *super_class;
     std::vector<CONSTANT_Class_info *> interfaces;
     std::vector<field_info> fields;
     std::vector<method_info> methods;
@@ -799,17 +801,19 @@ struct ClassFile {
     // Computes whether `this` is a subclass of `other` (regarding both `extends` and `implements`).
     // Note that `x.is_subclass_of(x) == false`
     bool is_subclass_of(ClassFile *other) {
+        if (this->super_class == other) {
+            return true;
+        }
         for (auto &i: interfaces) {
             if (i->clazz == other) {
                 return true;
             }
         }
-        if (this->super_class != nullptr &&
-            (this->super_class->clazz == other || this->super_class->clazz->is_subclass_of(other))) {
+        if (this->super_class != nullptr && this->super_class->is_subclass_of(other)) {
             return true;
         }
         for (auto &i: interfaces) {
-            if (i->clazz == other || i->clazz->is_subclass_of(other)) {
+            if (i->clazz->is_subclass_of(other)) {
                 return true;
             }
         }
@@ -819,6 +823,8 @@ struct ClassFile {
     [[nodiscard]] inline bool is_interface() const {
         return (access_flags & static_cast<u2>(ClassFileAccessFlags::ACC_INTERFACE)) != 0;
     }
+
+    [[nodiscard]] inline std::string const &name() const { return this_class->name->value; }
 };
 
 

src/classloading.cpp

@@ -1,4 +1,76 @@
+#include <filesystem>
+#include <utility>
+
 #include "classloading.hpp"
+#include "parser.hpp"
+#include "util.hpp"
+#include "zip.hpp"
+
+BootstrapClassLoader::BootstrapClassLoader(const std::string &bootclasspath) : class_path_entries(), buffer() {
+    // TODO fix hardcoded path
+    class_path_entries.push_back({"java.base", {}, "../jdk/exploded-modules/java.base", {}});
+
+    for (auto &path : split(bootclasspath, ':')) {
+        if (path.ends_with(".jar") || path.ends_with(".zip")) {
+            class_path_entries.push_back({"", {}, "", ZipArchive(path)});
+        } else {
+            class_path_entries.push_back({path, {}, path, {}});
+        }
+    }
+}
+
+// https://stackoverflow.com/a/7782037
+struct membuf : std::streambuf {
+    membuf(char *begin, char *end) {
+        this->setg(begin, begin, end);
+    }
+};
+
+ClassFile *BootstrapClassLoader::load(std::string const &name) {
+    for (auto &cp_entry : class_path_entries) {
+        if (auto loaded = cp_entry.class_files.find(name); loaded != cp_entry.class_files.end()) {
+            if (loaded->second == nullptr) {
+                continue;
+            }
+            return loaded->second.get();
+        }
+
+        std::unique_ptr<ClassFile> parsed{};
+
+        if (!cp_entry.directory.empty()) {
+            auto path = cp_entry.directory + "/" + name + ".class";
+            std::ifstream in{path, std::ios::in | std::ios::binary};
+
+            if (in) {
+                Parser parser{in};
+                parsed = std::make_unique<ClassFile>(parser.parse());
+            }
+        } else if (!cp_entry.zip.path.empty()) {
+            auto path = name + ".class";
+
+            if (ZipEntry const *zip_entry = cp_entry.zip.entry_for_path(path); zip_entry != nullptr) {
+                cp_entry.zip.read(*zip_entry, buffer);
+
+                membuf buf{buffer.data(), buffer.data() + buffer.size()};
+                std::istream in{&buf};
+
+                Parser parser{in};
+                parsed = std::make_unique<ClassFile>(parser.parse());
+            }
+        }
+
+        ClassFile *result = parsed.get();
+        cp_entry.class_files.insert({name, std::move(parsed)});
+
+        if (result != nullptr) {
+            if (name != result->name()) {
+                throw ParseError("unexpected name");
+            }
+            return result;
+        }
+    }
+    return nullptr;
+}
 
 static bool initialize_class(ClassFile *clazz, Thread &thread, Frame &frame) {
     for (const auto &field : clazz->fields) {
@@ -52,7 +124,7 @@ static bool initialize_class(ClassFile *clazz, Thread &thread, Frame &frame) {
 }
 
 
-bool resolve_class(std::unordered_map<std::string_view, ClassFile *> &class_files, CONSTANT_Class_info *class_info,
+bool resolve_class(BootstrapClassLoader &bootstrap_class_loader, CONSTANT_Class_info *class_info,
                    Thread &thread, Frame &frame) {
     if (class_info->clazz == nullptr) {
         auto &name = class_info->name->value;
@@ -62,12 +134,11 @@ bool resolve_class(std::unordered_map<std::string_view, ClassFile *> &class_file
 
         // TODO we also need to deal with array classes here. They also load the class for the elements.
 
-        auto result = class_files.find(name);
-        if (result == class_files.end()) {
+        ClassFile *clazz = bootstrap_class_loader.load(name);
+        if (clazz == nullptr) {
             // TODO this prints "A not found" if A was found but a superclass/interface wasn't
             throw std::runtime_error("class not found: '" + name + "'");
         }
-        ClassFile *clazz = result->second;
 
         if (clazz->resolved) {
             class_info->clazz = clazz;
@@ -80,13 +151,12 @@ bool resolve_class(std::unordered_map<std::string_view, ClassFile *> &class_file
         }
 
         size_t parent_instance_field_count = 0;
-        // TODO use stdlib
-        if (clazz->super_class != nullptr && clazz->super_class->name->value != "java/lang/Object" &&
-            clazz->super_class->name->value != "java/lang/Exception") {
-            auto runInitializer = resolve_class(class_files, clazz->super_class, thread, frame);
-            if (runInitializer)
-                return runInitializer;
-            parent_instance_field_count = clazz->super_class->clazz->total_instance_field_count;
+        if (clazz->super_class == nullptr && clazz->super_class_ref != nullptr) {
+            if (resolve_class(bootstrap_class_loader, clazz->super_class_ref, thread, frame))
+                return true;
+
+            clazz->super_class = clazz->super_class_ref->clazz;
+            parent_instance_field_count = clazz->super_class->total_instance_field_count;
         }
 
         // instance and static fields
@@ -105,7 +175,7 @@ bool resolve_class(std::unordered_map<std::string_view, ClassFile *> &class_file
         clazz->static_field_values.resize(clazz->fields.size() - clazz->declared_instance_field_count);
 
         for (auto &interface : clazz->interfaces) {
-            auto runInitializer = resolve_class(class_files, interface, thread, frame);
+            auto runInitializer = resolve_class(bootstrap_class_loader, interface, thread, frame);
             if (runInitializer)
                 return true;
         }
@@ -150,7 +220,7 @@ bool resolve_field_recursive(ClassFile *clazz, CONSTANT_Fieldref_info *field_inf
 
         if (clazz->super_class != nullptr) {
             // 3.
-            clazz = clazz->super_class->clazz;
+            clazz = clazz->super_class;
         } else {
             break;
         }

src/classloading.hpp

@@ -1,15 +1,38 @@
 #ifndef SCHOKOVM_CLASSLOADING_HPP
 #define SCHOKOVM_CLASSLOADING_HPP
 
+#include <optional>
 #include <unordered_map>
+
 #include "classfile.hpp"
 #include "interpreter.hpp"
+#include "zip.hpp"
+
+struct ClassPathEntry {
+    std::string module_name;
+    std::unordered_map<std::string, std::unique_ptr<ClassFile>> class_files;
+
+    // TODO use subtyping instead?
+    // TODO should module entries refer to other entries?
+    // one of those will be empty
+    std::string directory;
+    ZipArchive zip;
+};
+
+struct BootstrapClassLoader {
+    std::vector<ClassPathEntry> class_path_entries;
+    std::vector<char> buffer;
+
+    explicit BootstrapClassLoader(const std::string &bootclasspath);
+
+    ClassFile *load(std::string const &name);
+};
 
 /**
  * Throws if the class was not found
  * @return whether a stack frame for an initializer was pushed
  */
-bool resolve_class(std::unordered_map<std::string_view, ClassFile *> &class_files, CONSTANT_Class_info *class_info,
+bool resolve_class(BootstrapClassLoader &bootstrap_class_loader, CONSTANT_Class_info *class_info,
                    Thread &thread, Frame &frame);
 
 bool resolve_field_recursive(ClassFile *clazz, CONSTANT_Fieldref_info *field_info);