虐心短片之初识JVM

# define __alloca alloca

# define __stat stat

InitLauncher(javaw);	//java 启动器初始化

    DumpState();	// 输出程序状态信息

    if (JLI_IsTraceLauncher()) {	// 检查是否启用了启动器跟踪设置

        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);	 // 添加一个启动选项，用于启用 JVM 启动时的诊断信息

    }

···

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    SelectVersion(argc, argv, &main_class); // 选择 JRE 版本

CreateExecutionEnvironment(&argc, &argv,

                               jrepath, sizeof(jrepath),

                               jvmpath, sizeof(jvmpath),

                               jvmcfg,  sizeof(jvmcfg));

if (!LoadJavaVM(jvmpath, &ifn)) {

        return(6);

    }

LoadJavaVM(const char *jvmpath, InvocationFunctions *ifn)

{

    void *libjvm;

    JLI_TraceLauncher("JVM path is %s\n", jvmpath);

    libjvm = dlopen(jvmpath, RTLD_NOW + RTLD_GLOBAL);

    if (libjvm == NULL) {

#if defined(__solaris__) && defined(__sparc) && !defined(_LP64) /* i.e. 32-bit sparc */

      FILE * fp;

      Elf32_Ehdr elf_head;

      int count;

      int location;

      fp = fopen(jvmpath, "r");

      if (fp == NULL) {

        JLI_ReportErrorMessage(DLL_ERROR2, jvmpath, dlerror());

        return JNI_FALSE;

      }

      /* read in elf header */

      count = fread((void*)(&elf_head), sizeof(Elf32_Ehdr), 1, fp);

      fclose(fp);

      if (count < 1) {

        JLI_ReportErrorMessage(DLL_ERROR2, jvmpath, dlerror());

        return JNI_FALSE;

      }

      /*

       * Check for running a server vm (compiled with -xarch=v8plus)

       * on a stock v8 processor.  In this case, the machine type in

       * the elf header would not be included the architecture list

       * provided by the isalist command, which is turn is gotten from

       * sysinfo.  This case cannot occur on 64-bit hardware and thus

       * does not have to be checked for in binaries with an LP64 data

       * model.

       */

      if (elf_head.e_machine == EM_SPARC32PLUS) {

        char buf[257];  /* recommended buffer size from sysinfo man

                           page */

        long length;

        char* location;

        length = sysinfo(SI_ISALIST, buf, 257);

        if (length > 0) {

            location = JLI_StrStr(buf, "sparcv8plus ");

          if (location == NULL) {

            JLI_ReportErrorMessage(JVM_ERROR3);

            return JNI_FALSE;

          }

        }

      }

#endif

        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)

{

    ShowSplashScreen(); // 显示启动画面

    return ContinueInNewThread(ifn, threadStackSize, argc, argv, mode, what, ret);// 继续新线程

}

int ContinueInNewThread(InvocationFunctions* ifn, jlong threadStackSize,

                        int argc, char **argv,

                        int mode, char *what, int ret)

{

    // 如果用户未指定线程堆栈大小，检查虚拟机是否有首选堆栈大小

    if (threadStackSize == 0) {

        struct JDK1_1InitArgs args1_1;

        memset((void*)&args1_1, 0, sizeof(args1_1));

        args1_1.version = JNI_VERSION_1_1;

        ifn->GetDefaultJavaVMInitArgs(&args1_1);  /* 忽略返回值 */

        if (args1_1.javaStackSize > 0) {

            threadStackSize = args1_1.javaStackSize;

        }

    }

    // 创建一个新线程来创建 JVM 并调用主方法

    {

        JavaMainArgs args;

        int rslt;

        args.argc = argc;

        args.argv = argv;

        args.mode = mode;

        args.what = what;

        args.ifn = *ifn;

        rslt = ContinueInNewThread0(JavaMain, threadStackSize, (void*)&args);

        // 如果调用者认为存在错误，我们直接返回该错误值，否则返回调用者的返回值

        return (ret != 0) ? ret : rslt;

    }

}