Compiler JDK8
下載jdk8
開啟終端機，在Downloads目錄下，執行以下句子。
git clone https://github.com/openjdk/jdk8u
安裝一些工具
# 安装基础编译工具和依赖
brew install autoconf freetype ccache pkg-config
xcode-select --install # 确保Xcode命令行工具已安装
binutils
brew install binutils
echo 'export PATH="/usr/local/opt/binutils/bin:$PATH"' >> ~/.zshrc
# 立即生效
source ~/.zshrc
下載jdk7
為什麼要下載jdk7呢？
編譯的時候需要jdk8的前一個版本的jdk。
我是mac，我下載的bin目錄的位置在此處。
/Library/Java/JavaVirtualMachines/jdk1.7.0_80.jdk/Contents/Home
暫時設定Java Home
export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.7.0_80.jdk/Contents/Home
## 檢查版本
$JAVA_HOME/bin/java -version
要確保印出以下內容
java version "1.7.0_80"
Java(TM) SE Runtime Environment (build 1.7.0_80-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.80-b11, mixed mode)
編譯
進到jdk8的目錄
cd jdk8u
# 确保使用绝对路径
export OBJCOPY=$(which objcopy)
# 完整配置命令（必须在一行）
bash configure \
--with-boot-jdk=$JAVA_HOME \
--with-debug-level=slowdebug \
--enable-debug-symbols \
--with-native-debug-symbols=internal \
OBJCOPY=$OBJCOPY
make
make JOBS=2 images
若要重新make，請先clean
make clean
rm -rf build
檢查PrintVtables功能
檢查是否可以用PrintVtables功能
./build/macosx-x86_64-normal-server-slowdebug/jdk/bin/java -XX:+UnlockDiagnosticVMOptions -XX:+PrintVtables
JAVA_HOME
把build目錄中的編譯好的macosx-x86_64-normal-server-slowdebug，更改名jdk8_debug
修改zshrc
vi ~/.zshrc
export JAVA_HOME=/Users/cici/Downloads/jdk8u/build/jdk8_debug/jdk
export PATH=$JAVA_HOME/bin:$PATH
source ~/.zshrc
檢查版本
java -version
openjdk version "1.8.0_462-internal-debug"
OpenJDK Runtime Environment (build 1.8.0_462-internal-debug-cici_2025_05_27_10_21-b00)
OpenJDK 64-Bit Server VM (build 25.462-b00-debug, mixed mode)
測試
java -XX:+UnlockDiagnosticVMOptions -XX:+PrintVtables PolyExample
測試檔案
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class Animal {
public void speak() { System.out.println("Animal"); }
public void eat() { System.out.println("Animal eats"); }
}
class Dog extends Animal {
@Override public void speak() { System.out.println("Dog"); }
@Override public void eat() { System.out.println("Dog eats"); }
}
class SuperDog extends Dog {
@Override public void speak() { System.out.println("SuperDog"); }
@Override public void eat() { System.out.println("SuperDog eats"); }
}
public class TestVtable {
public static void main(String[] args) throws Exception {
for (int i = 0; i < 10000; i++) {
Animal a = getAnimal(i);
a.speak();
a.eat();
}
Thread.sleep(300_000); // 等待觀察
}
public static Animal getAnimal(int i) {
if (i % 2 == 0) return new SuperDog();
else return new Dog();
}
}
編譯
./build/macosx-x86_64-normal-server-slowdebug/jdk/bin/javac TestVtable
執行
./build/macosx-x86_64-normal-server-slowdebug/jdk/bin/java \
-Xcomp \
-XX:+UnlockDiagnosticVMOptions \
-XX:+PrintVtables \
-XX:+TraceClassLoading \
-XX:+TraceClassInitialization \
TestVtable 2>&1 | tee vtables.log
檔案中尋找vtable
grep -i vtable vtables.log
grep -A10 'Vtable for class' vtables.log