Java JVM(1) - 走进JVM

int main() {     //实现一个最简的a+b功能，并存入变量c
    int a = 10;
    int b = 20;
    int c = a + b;
    return c;
}

    .section   __TEXT,__text,regular,pure_instructions
   .build_version macos, 12, 0    sdk_version 12, 1
   .globl _main                           ; -- Begin function main
   .p2align   2
_main:                                  ; @main
   .cfi_startproc
; %bb.0:
   sub    sp, sp, #16                     ; =16
   .cfi_def_cfa_offset 16
   str    wzr, [sp, #12]
   mov    w8, #10
   str    w8, [sp, #8]
   mov    w8, #20
   str    w8, [sp, #4]
   ldr    w8, [sp, #8]
   ldr    w9, [sp, #4]
   add    w8, w8, w9
   str    w8, [sp]
   ldr    w0, [sp]
   add    sp, sp, #16                     ; =16
   ret
   .cfi_endproc
                                        ; -- End function
.subsections_via_symbols

public class Main {
    public int test(){    //和上面的例子一样
        int a = 10;
        int b = 20;
        int c = a + b;
        return c;
    }
}

...
public int test();
    descriptor: ()I
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=4, args_size=1
         0: bipush        10
         2: istore_1
         3: bipush        20
         5: istore_2
         6: iload_1
         7: iload_2
         8: iadd
         9: istore_3
        10: iload_3
        11: ireturn
      LineNumberTable:
        line 5: 0
        line 6: 3
        line 7: 6
        line 8: 10
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      12     0  this   Lcom/test/Main;
            3       9     1     a   I
            6       6     2     b   I
           10       2     3     c   I

descriptor: ()I     //参数以及返回值类型，()I就表示没有形式参数，返回值为基本类型int
flags: ACC_PUBLIC   //public访问权限
Code:
  stack=2, locals=4, args_size=1    //stack表示要用到的最大栈深度，本地变量数，堆栈上最大对象数量（这里指的是this）

0: bipush        10     //0是程序偏移地址，然后是指令，最后是操作数
2: istore_1

3: bipush        20
5: istore_2

6: iload_1
7: iload_2
8: iadd

9: istore_3
10: iload_3
11: ireturn

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.8 100
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.8 100

nagocoler@ubuntu-server:~$ gcc --version
gcc (Ubuntu 4.8.5-4ubuntu2) 4.8.5
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
nagocoler@ubuntu-server:~$ g++ --version
g++ (Ubuntu 4.8.5-4ubuntu2) 4.8.5
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

wget https://ftp.gnu.org/gnu/make/make-3.81.tar.gz
• 1

tar -zxvf make-3.81.tar.gz 
cd make-3.81/

...
#ifdef  HAVE_CONFIG_H
# include <config.h>
#endif
#define __alloca alloca   <- 添加这一句
/* Enable GNU extensions 
...

bash configure
sudo make install

nagocoler@ubuntu-server:~/make-3.81$ make -verison
GNU Make 3.81
Copyright (C) 2006  Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.

sudo apt install openjdk-8-jdk

unzip jdk-jdk8-b120.zip

bash configure --with-debug-level=slowdebug --enable-debug-symbols ZIP_DEBUGINFO_FIELS=0

Configuration summary:
* Debug level:    slowdebug
* JDK variant:    normal
* JVM variants:   server
* OpenJDK target: OS: linux, CPU architecture: x86, address length: 64
Tools summary:
* Boot JDK:       openjdk version "1.8.0_312" OpenJDK Runtime Environment (build 1.8.0_312-8u312-b07-0ubuntu1~20.04-b07) OpenJDK 64-Bit Server VM (build 25.312-b07, mixed mode)  (at /usr/lib/jvm/java-8-openjdk-amd64)
* C Compiler:     gcc-4.8 (Ubuntu 4.8.5-4ubuntu2) version 4.8.5 (at /usr/bin/gcc-4.8)
* C++ Compiler:   g++-4.8 (Ubuntu 4.8.5-4ubuntu2) version 4.8.5 (at /usr/bin/g++-4.8)
Build performance summary:
* Cores to use:   3
* Memory limit:   3824 MB
* ccache status:  not installed (consider installing)
WARNING: The result of this configuration has overridden an older
configuration. You *should* run 'make clean' to make sure you get a
proper build. Failure to do so might result in strange build problems.

原有的 WARNINGS_ARE_ERRORS = -Werror
修改为 #WARNINGS_ARE_ERRORS = -Werror

  $(CP) -R -p $(NASHORN_OUTPUTDIR)/nashorn_classes/* $(@D)/
  $(FIXPATH) $(JAVA) \
原有的 -cp "$(NASHORN_OUTPUTDIR)/nasgen_classes$(PATH_SEP)$(NASHORN_OUTPUTDIR)/nashorn_classes" \
修改为  -Xbootclasspath/p:"$(NASHORN_OUTPUTDIR)/nasgen_classes$(PATH_SEP)$(NASHORN_OUTPUTDIR)/nashorn_classes" \
   jdk.nashorn.internal.tools.nasgen.Main $(@D) jdk.nashorn.internal.objects $(@D)

make all

----- Build times -------
Start 2022-01-29 11:36:35
End   2022-01-29 11:48:20
00:00:30 corba
00:00:25 demos
00:02:39 docs
00:03:05 hotspot
00:00:27 images
00:00:17 jaxp
00:00:31 jaxws
00:03:02 jdk
00:00:38 langtools
00:00:11 nashorn
00:11:45 TOTAL
-------------------------
Finished building OpenJDK for target 'all'

/home/nagocoler/jdk-jdk8-b120/build/linux-x86_64-normal-server-slowdebug/jdk/bin/java -version
openjdk version "1.8.0-internal-debug"
OpenJDK Runtime Environment (build 1.8.0-internal-debug-nagocoler_2022_01_29_11_36-b00)
OpenJDK 64-Bit Server VM (build 25.0-b62-debug, mixed mode)
Process finished with exit code 0

public class Main{
        public static void main(String[] args){
                System.out.println("Hello World!");
        }       
}       

/home/nagocoler/jdk-jdk8-b120/build/linux-x86_64-normal-server-slowdebug/jdk/bin/java Main
Hello World!
Process finished with exit code 0

int
JLI_Launch(int argc, char ** argv,              /* main argc, argc */
        int jargc, const char** jargv,          /* java args */
        int appclassc, const char** appclassv,  /* app classpath */
        const char* fullversion,                /* full version defined */
        const char* dotversion,                 /* dot version defined */
        const char* pname,                      /* program name */
        const char* lname,                      /* launcher name */
        jboolean javaargs,                      /* JAVA_ARGS */
        jboolean cpwildcard,                    /* classpath wildcard */
        jboolean javaw,                         /* windows-only javaw */
        jint     ergo_class                     /* ergnomics policy */
);

InitLauncher(javaw);
DumpState();
if (JLI_IsTraceLauncher()) {
    int i;
    printf("Command line args:\n");
    for (i = 0; i < argc ; i++) {
        printf("argv[%d] = %s\n", i, argv[i]);
    }
    AddOption("-Dsun.java.launcher.diag=true", NULL);
}

/*
 * Make sure the specified version of the JRE is running.
 *
 * There are three things to note about the SelectVersion() routine:
 *  1) If the version running isn't correct, this routine doesn't
 *     return (either the correct version has been exec'd or an error
 *     was issued).
 *  2) Argc and Argv in this scope are *not* altered by this routine.
 *     It is the responsibility of subsequent code to ignore the
 *     arguments handled by this routine.
 *  3) As a side-effect, the variable "main_class" is guaranteed to
 *     be set (if it should ever be set).  This isn't exactly the
 *     poster child for structured programming, but it is a small
 *     price to pay for not processing a jar file operand twice.
 *     (Note: This side effect has been disabled.  See comment on
 *     bugid 5030265 below.)
 */
SelectVersion(argc, argv, &main_class);

CreateExecutionEnvironment(&argc, &argv,
                               jrepath, sizeof(jrepath),
                               jvmpath, sizeof(jvmpath),
                               jvmcfg,  sizeof(jvmcfg));

if (!LoadJavaVM(jvmpath, &ifn)) {
    return(6);
}

jboolean
LoadJavaVM(const char *jvmpath, InvocationFunctions *ifn)
{
    Dl_info dlinfo;
    void *libjvm;
    JLI_TraceLauncher("JVM path is %s\n", jvmpath);
    libjvm = dlopen(jvmpath, RTLD_NOW + RTLD_GLOBAL);
    if (libjvm == NULL) {
        JLI_ReportErrorMessage(DLL_ERROR1, __LINE__);
        JLI_ReportErrorMessage(DLL_ERROR2, jvmpath, dlerror());
        return JNI_FALSE;
    }
    ifn->CreateJavaVM = (CreateJavaVM_t)
        dlsym(libjvm, "JNI_CreateJavaVM");
    if (ifn->CreateJavaVM == NULL) {
        JLI_ReportErrorMessage(DLL_ERROR2, jvmpath, dlerror());
        return JNI_FALSE;
    }
    ifn->GetDefaultJavaVMInitArgs = (GetDefaultJavaVMInitArgs_t)
        dlsym(libjvm, "JNI_GetDefaultJavaVMInitArgs");
    if (ifn->GetDefaultJavaVMInitArgs == NULL) {
        JLI_ReportErrorMessage(DLL_ERROR2, jvmpath, dlerror());
        return JNI_FALSE;
    }
    ifn->GetCreatedJavaVMs = (GetCreatedJavaVMs_t)
    dlsym(libjvm, "JNI_GetCreatedJavaVMs");
    if (ifn->GetCreatedJavaVMs == NULL) {
        JLI_ReportErrorMessage(DLL_ERROR2, jvmpath, dlerror());
        return JNI_FALSE;
    }
    return JNI_TRUE;
}

return JVMInit(&ifn, threadStackSize, argc, argv, mode, what, ret);

int
JVMInit(InvocationFunctions* ifn, jlong threadStackSize,
                 int argc, char **argv,
                 int mode, char *what, int ret) {
    if (sameThread) {
        //无需关心....
    } else {
        //正常情况下走这个
        return ContinueInNewThread(ifn, threadStackSize, argc, argv, mode, what, ret);
    }
}

int
ContinueInNewThread(InvocationFunctions* ifn, jlong threadStackSize,
                    int argc, char **argv,
                    int mode, char *what, int ret)
{
    ...
      rslt = ContinueInNewThread0(JavaMain, threadStackSize, (void*)&args);
      /* If the caller has deemed there is an error we
       * simply return that, otherwise we return the value of
       * the callee
       */
      return (ret != 0) ? ret : rslt;
    }
}

int
ContinueInNewThread0(int (JNICALL *continuation)(void *), jlong stack_size, void * args) {
    int rslt;
    pthread_t tid;
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
    if (stack_size > 0) {
      pthread_attr_setstacksize(&attr, stack_size);
    }
    if (pthread_create(&tid, &attr, (void *(*)(void*))continuation, (void*)args) == 0) {
      void * tmp;
      pthread_join(tid, &tmp);
      rslt = (int)tmp;
    } else {
     /*
      * Continue execution in current thread if for some reason (e.g. out of
      * memory/LWP)  a new thread can't be created. This will likely fail
      * later in continuation as JNI_CreateJavaVM needs to create quite a
      * few new threads, anyway, just give it a try..
      */
      rslt = continuation(args);
    }
    pthread_attr_destroy(&attr);
    return rslt;
}

/* Initialize the virtual machine */
start = CounterGet();
if (!InitializeJVM(&vm, &env, &ifn)) {
    JLI_ReportErrorMessage(JVM_ERROR1);
    exit(1);
}

/*
 * Get the application's main class.
 *
 * See bugid 5030265.  The Main-Class name has already been parsed
 * from the manifest, but not parsed properly for UTF-8 support.
 * Hence the code here ignores the value previously extracted and
 * uses the pre-existing code to reextract the value.  This is
 * possibly an end of release cycle expedient.  However, it has
 * also been discovered that passing some character sets through
 * the environment has "strange" behavior on some variants of
 * Windows.  Hence, maybe the manifest parsing code local to the
 * launcher should never be enhanced.
 *
 * Hence, future work should either:
 *     1)   Correct the local parsing code and verify that the
 *          Main-Class attribute gets properly passed through
 *          all environments,
 *     2)   Remove the vestages of maintaining main_class through
 *          the environment (and remove these comments).
 *
 * This method also correctly handles launching existing JavaFX
 * applications that may or may not have a Main-Class manifest entry.
 */
mainClass = LoadMainClass(env, mode, what);

/*
 * In some cases when launching an application that needs a helper, e.g., a
 * JavaFX application with no main method, the mainClass will not be the
 * applications own main class but rather a helper class. To keep things
 * consistent in the UI we need to track and report the application main class.
 */
appClass = GetApplicationClass(env);

/*
 * PostJVMInit uses the class name as the application name for GUI purposes,
 * for example, on OSX this sets the application name in the menu bar for
 * both SWT and JavaFX. So we'll pass the actual application class here
 * instead of mainClass as that may be a launcher or helper class instead
 * of the application class.
 */
PostJVMInit(env, appClass, vm);

/*
 * The LoadMainClass not only loads the main class, it will also ensure
 * that the main method's signature is correct, therefore further checking
 * is not required. The main method is invoked here so that extraneous java
 * stacks are not in the application stack trace.
 */
mainID = (*env)->GetStaticMethodID(env, mainClass, "main",
                                   "([Ljava/lang/String;)V");

/* Invoke main method. */
(*env)->CallStaticVoidMethod(env, mainClass, mainID, mainArgs);

/*
 * The launcher's exit code (in the absence of calls to
 * System.exit) will be non-zero if main threw an exception.
 */
ret = (*env)->ExceptionOccurred(env) == NULL ? 0 : 1;
LEAVE();
/*

javah -classpath out/production/SimpleHelloWorld -d ./jni com.test.Main

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_test_Main */
#ifndef _Included_com_test_Main
#define _Included_com_test_Main
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_test_Main
 * Method:    sum
 * Signature: (II)V
 */
JNIEXPORT void JNICALL Java_com_test_Main_sum
  (JNIEnv *, jclass, jint, jint);
#ifdef __cplusplus
}
#endif
#endif

cmake_minimum_required(VERSION 3.21)
project(JNITest)
include_directories(/Library/Java/JavaVirtualMachines/zulu-8.jdk/Contents/Home/include)
include_directories(/Library/Java/JavaVirtualMachines/zulu-8.jdk/Contents/Home/include/darwin)
set(CMAKE_CXX_STANDARD 14)
add_executable(JNITest com_test_Main.cpp com_test_Main.h)

gcc com_test_Main.cpp -I /Library/Java/JavaVirtualMachines/zulu-8.jdk/Contents/Home/include -I /Library/Java/JavaVirtualMachines/zulu-8.jdk/Contents/Home/include/darwin -fPIC -shared -o test.dylib -lstdc++

public class Main {
    static {
        System.load("/Users/nagocoler/Desktop/test.dylib");
    }
    public static void main(String[] args) {
        System.out.println(sum(1, 2));
    }
    public static native int sum(int a, int b);
}