西北工业大学操作系统实验实验报告一、实验目的掌握在GeekOS系统用户态模式下加载并运行可执行程序的方法。
二、实验要求1. 按照实验讲义P127页中的设计要求，实现在用户态模式下加载并运行可执行程序的代码，给出关键函数的代码以及实验结果。
三、实验过程及结果答：核心函数代码如下：================== user.c ===============//产生一个进程（用户态）int Spawn(const char *program, const char *command, struct Kernel_Thread **pThread) {//TODO("Spawn a process by reading an executable from a filesystem");int rc;char *exeFileData = 0;ulong_t exeFileLength;struct User_Context *userContext = 0;struct Kernel_Thread *process = 0;struct Exe_Format exeFormat;if ((rc = Read_Fully(program, (void**) &exeFileData, &exeFileLength)) != 0 ){Print("Failed to Read File %s!\n", program);goto fail;}if((rc = Parse_ELF_Executable(exeFileData, exeFileLength, &exeFormat)) != 0 ){Print("Failed to Parse ELF File!\n");goto fail;}if((rc = Load_User_Program(exeFileData, exeFileLength, &exeFormat, command, &userContext)) != 0){Print("Failed to Load User Program!\n");goto fail;}//在堆分配方式下释放内存并再次初始化exeFileDataFree(exeFileData);exeFileData = 0;/* 开始用户进程,调用Start_User_Thread函数创建一个进程并使其进入准备运行队列*/ process = Start_User_Thread(userContext, false);if (process != 0) {KASSERT(process->refCount == 2);/* 返回核心进程的指针*/*pThread = process;rc = process->pid;//记录当前进程的ID}elserc = ENOMEM;return rc;fail: //如果新进程创建失败则注销User_Context对象if (exeFileData != 0)Free(exeFileData);//释放内存if (userContext != 0)Destroy_User_Context(userContext);//销毁进程对象return rc;}-------------------------------------//切换至用户上下文void Switch_To_User_Context(struct Kernel_Thread* kthread, struct Interrupt_State* state){static struct User_Context* s_currentUserContext; /* last user context used *///extern int userDebug;struct User_Context* userContext = kthread->userContext;KASSERT(!Interrupts_Enabled());if (userContext == 0) { //userContext为0表示此进程为核心态进程就不用切换地址空间return;}if (userContext != s_currentUserContext) {ulong_t esp0;//if (userDebug) Print("A[%p]\n", kthread);Switch_To_Address_Space(userContext);//为用户态进程时则切换地址空间esp0 = ((ulong_t) kthread->stackPage) + PAGE_SIZE;//if (userDebug)// Print("S[%lx]\n", esp0);/* 新进程的核心栈. */Set_Kernel_Stack_Pointer(esp0);//设置内核堆栈指针/* New user context is active */s_currentUserContext = userContext;}}================== elf.c ====================int Parse_ELF_Executable(char *exeFileData, ulong_t exeFileLength, struct Exe_Format *exeFormat){int i;elfHeader *head=(elfHeader*)exeFileData;programHeader *proHeader=(programHeader *)(exeFileData+head->phoff);KASSERT(exeFileData!=NULL);KASSERT(exeFileLength>head->ehsize+head->phentsize*head->phnum);KASSERT(head->entry%4==0);exeFormat->numSegments=head->phnum;exeFormat->entryAddr=head->entry;for(i=0;i<head->phnum;i++){exeFormat->segmentList[i].offsetInFile=proHeader->offset;exeFormat->segmentList[i].lengthInFile=proHeader->fileSize;exeFormat->segmentList[i].startAddress=proHeader->vaddr;exeFormat->segmentList[i].sizeInMemory=proHeader->memSize;exeFormat->segmentList[i].protFlags=proHeader->flags;proHeader++;}return 0;}=================== userseg.c ===================//需在此文件各函数前增加一个函数，此函数的功能是按给定的大小创建一个用户级进程上下文，具体实现如下：//函数功能:按给定的大小创建一个用户级进程上下文static struct User_Context* Create_User_Context(ulong_t size){struct User_Context * UserContext;size = Round_Up_To_Page(size);UserContext = (struct User_Context *)Malloc(sizeof(struct User_Context));if (UserContext != 0)UserContext->memory = Malloc(size);//为核心态进程elsegoto fail;//内存为空if (0 == UserContext->memory)goto fail;memset(UserContext->memory, '\0', size);UserContext->size = size;//以下为用户态进程创建LDT(段描述符表)//新建一个LDT描述符UserContext->ldtDescriptor = Allocate_Segment_Descriptor();if (0 == UserContext->ldtDescriptor)goto fail;//初始化段描述符Init_LDT_Descriptor(UserContext->ldtDescriptor, UserContext->ldt, NUM_USER_LDT_ENTRIES);//新建一个LDT选择子UserContext->ldtSelector = Selector(KERNEL_PRIVILEGE, true, Get_Descriptor_Index(UserContext->ldtDescriptor));//新建一个文本段描述符Init_Code_Segment_Descriptor(&UserContext->ldt[0],(ulong_t) UserContext->memory,size / PAGE_SIZE,USER_PRIVILEGE);//新建一个数据段Init_Data_Segment_Descriptor(&UserContext->ldt[1],(ulong_t) UserContext->memory,size / PAGE_SIZE,USER_PRIVILEGE);//新建数据段和文本段选择子UserContext->csSelector = Selector(USER_PRIVILEGE, false, 0);UserContext->dsSelector = Selector(USER_PRIVILEGE, false, 1);//将引用数清0UserContext->refCount = 0;return UserContext;fail:if (UserContext != 0){if (UserContext->memory != 0){Free(UserContext->memory);}Free(UserContext);}return 0;}--------------------------------------------//摧毁用户上下文void Destroy_User_Context(struct User_Context* userContext){//TODO("Destroy a User_Context");//释放占用的LDTFree_Segment_Descriptor(userContext->ldtDescriptor);userContext->ldtDescriptor=0;//释放内存空间Free(userContext->memory);userContext->memory=0;//释放userContext本身占用的内存Free(userContext);userContext=0;}----------------------------------------------int Load_User_Program(char *exeFileData,ulong_t exeFileLength,struct Exe_Format *exeFormat,const char *command,struct User_Context **pUserContext){//TODO("Load a user executable into a user memory space using segmentation");int i;ulong_t maxva = 0;//要分配的最大内存空间unsigned numArgs;//进程数目ulong_t argBlockSize;//参数块的大小ulong_t size, argBlockAddr;//参数块地址struct User_Context *userContext = 0;//计算用户态进程所需的最大内存空间for (i = 0; i < exeFormat->numSegments; ++i) {//elf.hstruct Exe_Segment *segment = &exeFormat->segmentList[i];ulong_t topva = segment->startAddress + segment->sizeInMemory; /* FIXME: range check */if (topva > maxva)maxva = topva;}Get_Argument_Block_Size(command, &numArgs, &argBlockSize);//获取参数块信息size = Round_Up_To_Page(maxva) + DEFAULT_USER_STACK_SIZE;argBlockAddr = size;size += argBlockSize;userContext = Create_User_Context(size);//按相应大小创建一个进程if (userContext == 0)//如果为核心态进程return -1;for (i = 0; i < exeFormat->numSegments; ++i) {struct Exe_Segment *segment = &exeFormat->segmentList[i];//根据段信息将用户程序中的各段内容复制到分配的用户内存空间memcpy(userContext->memory + segment->startAddress, exeFileData + segment->offsetInFile,segment->lengthInFile);}//格式化参数块Format_Argument_Block(userContext->memory + argBlockAddr, numArgs, argBlockAddr, command);//初始化数据段，堆栈段及代码段信息userContext->entryAddr = exeFormat->entryAddr;userContext->argBlockAddr = argBlockAddr;userContext->stackPointerAddr = argBlockAddr;//将初始化完毕的User_Context赋给*pUserContext*pUserContext = userContext;return 0;//成功}----------------------------------------------//将用户态的进程复制到内核缓冲区bool Copy_From_User(void* destInKernel, ulong_t srcInUser, ulong_t bufSize){struct User_Context * UserContext = g_currentThread->userContext;//--: check if memory if validatedif (!Validate_User_Memory(UserContext,srcInUser, bufSize))return false;memcpy(destInKernel, UserContext->memory + srcInUser, bufSize);return true;}-----------------------------------------//将内核态的进程复制到用户态bool Copy_To_User(ulong_t destInUser, void* srcInKernel, ulong_t bufSize){struct User_Context * UserContext = g_currentThread->userContext;if (!Validate_User_Memory(UserContext, destInUser, bufSize))return false;memcpy(UserContext->memory + destInUser, srcInKernel, bufSize);return true;}----------------------------------------//切换到用户地址空间void Switch_To_Address_Space(struct User_Context *userContext){ushort_t ldtSelector= userContext->ldtSelector;/* Switch to the LDT of the new user context */__asm__ __volatile__ ("lldt %0"::"a"(ldtSelector));}================= kthread.c ===============添加头文件#include <geekos/user.h>----------------------------------//创建一个用户进程/*static*/ void Setup_User_Thread(struct Kernel_Thread* kthread, struct User_Context* userContext){ulong_t eflags = EFLAGS_IF;unsigned csSelector=userContext->csSelector;//CS选择子unsigned dsSelector=userContext->dsSelector;//DS选择子Attach_User_Context(kthread, userContext);//初始化用户态进程堆栈，使之看上去像刚被中断运行一样//分别调用Push函数将以下数据压入堆栈Push(kthread, dsSelector); //数据选择子Push(kthread, userContext->stackPointerAddr); //堆栈指针Push(kthread, eflags); //EflagsPush(kthread, csSelector); //文本选择子Push(kthread, userContext->entryAddr); //程序计数器Push(kthread, 0); //错误代码(0)Push(kthread, 0); //中断号(0)//初始化通用寄存单元，将ESI用户传递参数块地址Push(kthread, 0); /* eax */Push(kthread, 0); /* ebx */Push(kthread, 0); /* edx */Push(kthread, 0); /* edx */Push(kthread, userContext->argBlockAddr); /* esi */Push(kthread, 0); /* edi */Push(kthread, 0); /* ebp *///初始化数据段寄存单元Push(kthread, dsSelector); /* ds */Push(kthread, dsSelector); /* es */Push(kthread, dsSelector); /* fs */Push(kthread, dsSelector); /* gs */}//开始用户进程struct Kernel_Thread* Start_User_Thread(struct User_Context* userContext, bool detached) {struct Kernel_Thread* kthread = Create_Thread(PRIORITY_USER, detached);if (kthread != 0){Setup_User_Thread(kthread, userContext);Make_Runnable_Atomic(kthread);}return kthread;}================ syscall.c =================//需在此文件别的函数前增加一个函数，函数名为Copy_User_String，它被函数Sys_PrintString调用，具体实现如下：static int Copy_User_String(ulong_t uaddr, ulong_t len, ulong_t maxLen, char **pStr) { int rc = 0;char *str;if (len > maxLen){ //超过最大长度return EINV ALID;}str = (char*) Malloc(len+1); //为字符串分配空间if (0 == str){rc = ENOMEM;goto fail;}if (!Copy_From_User(str, uaddr, len)){ //从用户空间中复制数据rc = EINV ALID;Free(str);goto fail;}str[len] = '\0';//成功*pStr = str;fail:return rc;}-----------------------------------------static int Sys_Exit(struct Interrupt_State* state){Exit(state->ebx);}-----------------------------------------static int Sys_PrintString(struct Interrupt_State* state){int rc = 0;//返回值uint_t length = state->ecx;//字符串长度uchar_t* buf = 0;if (length > 0) {if ((rc = Copy_User_String(state->ebx, length, 1023, (char**) &buf)) != 0) goto done;Put_Buf(buf, length);}done:if (buf != 0)Free(buf);return rc;}----------------------------------------------static int Sys_GetKey(struct Interrupt_State* state){return Wait_For_Key(); //返回按键码keyboard.c/Wait_For_Key()}---------------------------------------------static int Sys_SetAttr(struct Interrupt_State* state){Set_Current_Attr((uchar_t) state->ebx);return 0;}---------------------------------------------static int Sys_GetCursor(struct Interrupt_State* state){int row, col;Get_Cursor(&row, &col);if (!Copy_To_User(state->ebx, &row, sizeof(int)) ||!Copy_To_User(state->ecx, &col, sizeof(int)))return -1;return 0;}-----------------------------------------------static int Sys_PutCursor(struct Interrupt_State* state){return Put_Cursor(state->ebx, state->ecx) ? 0 : -1;}-----------------------------------------------static int Sys_Spawn(struct Interrupt_State* state){int rc; //函数返回值char *program = 0; //进程名称char *command = 0; //用户命令struct Kernel_Thread *process;if ((rc = Copy_User_String(state->ebx, state->ecx, VFS_MAX_PATH_LEN, &program)) != 0){goto fail;}if(rc = Copy_User_String(state->edx, state->esi, 1023, &command)) != 0){//从用户空间复制用户命令goto fail;}Enable_Interrupts(); //开中断rc = Spawn(program, command, &process);//得到进程名称和用户命令后便可生成一个新进程if (rc == 0) {//若成功则返回新进程ID号KASSERT(process != 0);rc = process->pid;}Disable_Interrupts();//关中断fail://返回小于0的错误代码if (program != 0)Free(program);if (command != 0)Free(command);return rc;}-----------------------------------------static int Sys_Wait(struct Interrupt_State* state){ //TODO("Wait system call");int exitCode;struct Kernel_Thread *kthread = Lookup_Thread(state->ebx);if (kthread == 0)return -12;Enable_Interrupts();exitCode = Join(kthread);Disable_Interrupts();return exitCode;}---------------------------------------static int Sys_GetPID(struct Interrupt_State* state){ //TODO("GetPID system call");return g_currentThread->pid;}================= main.c ==================static void Spawn_Init_Process(void){ //TODO("Spawn the init process");struct Kernel_Thread *pThread;Spawn("/c/shell.exe","/c/shell.exe",&pThread);}实验结果如图所示：原理：Geekos 提供了一个简单的shell，保存在PFAT文件系统内，所以geekos 系统启动后，启动shell程序/c/shell.exe运行，将/c/shell.exe作为可执行文件传递给spawn函数的program参数，创建第一个用户态进程，然后由它来创建其他进程。
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