深入理解JVM中call_stub：Java调用入口详解
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更新于2024-08-05
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在深入理解Java虚拟机（JVM）内部工作机制时，"call_stub"是一个关键的概念，它涉及到Java方法调用过程中的一个底层实现细节。"call_stub"通常在Java编译后的字节码执行阶段起作用，作为Java调用的入口点之一。当我们看到"JavaCalls::call_helper()"这一部分的代码，这表明调用助手函数是执行过程的起点。
首先，"call_helper()"函数位于"javaCalls.cpp"文件的第3930行，这是Java内部调用链的一部分，负责处理一些基础的调用操作。这个函数可能包括参数传递、异常处理等准备工作。接着，执行跳转到"os::os_exception_wrapper()"，这是一个操作系统相关的异常处理机制，确保在遇到错误时能正确回溯并捕获异常。
"JavaCalls::call()"函数是更进一步的调用过程，该函数的地址为0x7ffff70f2fe6，它具体执行Java方法的调用逻辑，包括查找目标方法、获取方法描述符、准备参数等。在方法调用之前，InstanceKlass类扮演着重要角色，因为"InstanceKlass::call_class_initializer()"和"InstanceKlass::initialize()"方法负责初始化类加载器加载的类，确保类变量和静态初始化块的执行。
"InstanceKlass::initialize_impl()"是类初始化的核心函数，它在不同的上下文中可能被多次调用，如"initialize()"和"initialize()"的内部实现"initialize_impl()"。这里涉及类的静态成员初始化和实例化的过程，确保类结构的完整性和正确性。
整个调用链展示了Java调用从最底层的系统调用到类初始化，再到最终方法执行的逐步过程。通过分析这些函数，我们可以理解JVM如何将Java字节码转换为可执行的操作，并在运行时处理各种异常情况，从而保证程序的正常运行。理解这些内部细节对于深入研究JVM优化、性能分析以及异常排查都有重要意义。
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https://liuxiaofei.com.cn/blog/call_stub-jvm-java%E8%B0%83%E7%94%A8%E7%9A%84%E5%85%A5%E5%8F%A3/
call_stub–JVM Java
Content:
call_helper
call_stub
call_stub
--------
JavaCalls::call_helper() at javaCalls.cpp:393 0x7ffff70f3600
os::os_exception_wrapper() at os_linux.cpp:5,104 0x7ffff7372b40
JavaCalls::call() at javaCalls.cpp:307 0x7ffff70f2fe6
InstanceKlass::call_class_initializer_impl() at instanceKlass.cpp:1,193 0x7ffff7088edf
InstanceKlass::call_class_initializer() at instanceKlass.cpp:1,161 0x7ffff7088c6d
InstanceKlass::initialize_impl() at instanceKlass.cpp:897 0x7ffff7087a40
InstanceKlass::initialize() at instanceKlass.cpp:557 0x7ffff7085f3e
InstanceKlass::initialize_impl() at instanceKlass.cpp:840 0x7ffff70874d7
InstanceKlass::initialize() at instanceKlass.cpp:557 0x7ffff7085f3e
initialize_class() at thread.cpp:983 0x7ffff74c5244
Threads::create_vm() at thread.cpp:3,497 0x7ffff74cc7df
JNI_CreateJavaVM() at jni.cpp:5,166 0x7ffff7134f13
call_helper
-----------------------------------------------
void JavaCalls::call_helper(JavaValue* result, methodHandle* m, JavaCallArguments* args, TRAPS) {
//JVM
OOP-Klass
Java
-
Handle
OOP
Klass
//Handle
()
->,
method()
method->
methodOop
methodHandle method = *m;
JavaThread* thread = (JavaThread*)THREAD;
assert(thread->is_Java_thread(), "must be called by a java thread");
assert(method.not_null(), "must have a method to call");
assert(!SafepointSynchronize::is_at_safepoint(), "call to Java code during VM operation");
assert(!thread->handle_area()->no_handle_mark_active(), "cannot call out to Java here");
CHECK_UNHANDLED_OOPS_ONLY(thread->clear_unhandled_oops();)
// Verify the arguments
if (CheckJNICalls) {
args->verify(method, result->get_type(), thread);
}
else debug_only(args->verify(method, result->get_type(), thread));
// Ignore call if method is empty
if (method->is_empty_method()) {
assert(result->get_type() == T_VOID, "an empty method must return a void value");
return;
}
#ifdef ASSERT
{ InstanceKlass* holder = method->method_holder();
// A klass might not be initialized since JavaCall's might be used during the executing of
// the . For example, a Thread.start might start executing on an object that is
// not fully initialized! (bad Java programming style)
assert(holder->is_linked(), "rewritting must have taken place");
}
#endif
assert(!thread->is_Compiler_thread(), "cannot compile from the compiler");
if (CompilationPolicy::must_be_compiled(method)) {
CompileBroker::compile_method(method, InvocationEntryBci,
CompilationPolicy::policy()->initial_compile_level(),
methodHandle(), 0, "must_be_compiled", CHECK);
}
//
method
entry_point,entry_point
Java
,
method
//
entry_point
//entry_point
method
,
method
entry_point
// Since the call stub sets up like the interpreter we call the from_interpreted_entry
// so we can go compiled via a i2c. Otherwise initial entry method will always
// run interpreted.
address entry_point = method->from_interpreted_entry();
if (JvmtiExport::can_post_interpreter_events() && thread->is_interp_only_mode()) {
entry_point = method->interpreter_entry();
}
// Figure out if the result value is an oop or not (Note: This is a different value
// than result_type. result_type will be T_INT of oops. (it is about size)
BasicType result_type = runtime_type_from(result);
bool oop_result_flag = (result->get_type() == T_OBJECT || result->get_type() == T_ARRAY);
// NOTE: if we move the computation of the result_val_address inside
// the call to call_stub, the optimizer produces wrong code.
intptr_t* result_val_address = (intptr_t*)(result->get_value_addr());
.call_stub–JVM Java
.txt 1/1/2020 8:16 AM
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