/* See COPYRIGHT for copyright information. */ #include <inc/x86.h> #include <inc/mmu.h> #include <inc/error.h> #include <inc/string.h> #include <inc/assert.h> #include <inc/elf.h> #include <kern/env.h> #include <kern/pmap.h> #include <kern/trap.h> #include <kern/monitor.h> #include <kern/sched.h> #include <kern/cpu.h> #include <kern/spinlock.h> struct Env *envs = NULL; // All environments static struct Env *env_free_list; // Free environment list // (linked by Env->env_link) #define ENVGENSHIFT 12 // >= LOGNENV // Global descriptor table. // // Set up global descriptor table (GDT) with separate segments for // kernel mode and user mode. Segments serve many purposes on the x86. // We don't use any of their memory-mapping capabilities, but we need // them to switch privilege levels. // // The kernel and user segments are identical except for the DPL. // To load the SS register, the CPL must equal the DPL. Thus, // we must duplicate the segments for the user and the kernel. // // In particular, the last argument to the SEG macro used in the // definition of gdt specifies the Descriptor Privilege Level (DPL) // of that descriptor: 0 for kernel and 3 for user. // struct Segdesc gdt[NCPU + 5] = { // 0x0 - unused (always faults -- for trapping NULL far pointers) SEG_NULL, // 0x8 - kernel code segment [GD_KT >> 3] = SEG(STA_X | STA_R, 0x0, 0xffffffff, 0), // 0x10 - kernel data segment [GD_KD >> 3] = SEG(STA_W, 0x0, 0xffffffff, 0), // 0x18 - user code segment [GD_UT >> 3] = SEG(STA_X | STA_R, 0x0, 0xffffffff, 3), // 0x20 - user data segment [GD_UD >> 3] = SEG(STA_W, 0x0, 0xffffffff, 3), // Per-CPU TSS descriptors (starting from GD_TSS0) are initialized // in trap_init_percpu() // [GD_TSS0 >> 3] = SEG_NULL }; struct Pseudodesc gdt_pd = { sizeof(gdt) - 1, (unsigned long) gdt }; // // Converts an envid to an env pointer. // If checkperm is set, the specified environment must be either the // current environment or an immediate child of the current environment. // // RETURNS // 0 on success, -E_BAD_ENV on error. // On success, sets *env_store to the environment. // On error, sets *env_store to NULL. // int envid2env(envid_t envid, struct Env **env_store, bool checkperm) { struct Env *e; // If envid is zero, return the current environment. if (envid == 0) { *env_store = curenv; return 0; } // Look up the Env structure via the index part of the envid, // then check the env_id field in that struct Env // to ensure that the envid is not stale // (i.e., does not refer to a _previous_ environment // that used the same slot in the envs[] array). e = &envs[ENVX(envid)]; if (e->env_status == ENV_FREE || e->env_id != envid) { *env_store = 0; return -E_BAD_ENV; } // Check that the calling environment has legitimate permission // to manipulate the specified environment. // If checkperm is set, the specified environment // must be either the current environment // or an immediate child of the current environment. if (checkperm && e != curenv && e->env_parent_id != curenv->env_id) { *env_store = 0; return -E_BAD_ENV; } *env_store = e; return 0; } // Mark all environments in 'envs' as free, set their env_ids to 0, // and insert them into the env_free_list. // Make sure the environments are in the free list in the same order // they are in the envs array (i.e., so that the first call to // env_alloc() returns envs[0]). // void env_init(void) { // Set up envs array // LAB 3: Your code here. for (int i = NENV - 1; i >= 0; i--) { envs[i].env_id = 0; envs[i].env_link = env_free_list; env_free_list = envs + i; } // Per-CPU part of the initialization env_init_percpu(); } // Load GDT and segment descriptors. void env_init_percpu(void) { lgdt(&gdt_pd); // The kernel never uses GS or FS, so we leave those set to // the user data segment. asm volatile("movw %%ax,%%gs" : : "a" (GD_UD|3)); asm volatile("movw %%ax,%%fs" : : "a" (GD_UD|3)); // The kernel does use ES, DS, and SS. We'll change between // the kernel and user data segments as needed. asm volatile("movw %%ax,%%es" : : "a" (GD_KD)); asm volatile("movw %%ax,%%ds" : : "a" (GD_KD)); asm volatile("movw %%ax,%%ss" : : "a" (GD_KD)); // Load the kernel text segment into CS. asm volatile("ljmp %0,$1f\n 1:\n" : : "i" (GD_KT)); // For good measure, clear the local descriptor table (LDT), // since we don't use it. lldt(0); } // // Initialize the kernel virtual memory layout for environment e. // Allocate a page directory, set e->env_pgdir accordingly, // and initialize the kernel portion of the new environment's address space. // Do NOT (yet) map anything into the user portion // of the environment's virtual address space. // // Returns 0 on success, < 0 on error. Errors include: // -E_NO_MEM if page directory or table could not be allocated. // static int env_setup_vm(struct Env *e) { int i; struct PageInfo *p = NULL; // Allocate a page for the page directory if (!(p = page_alloc(ALLOC_ZERO))) return -E_NO_MEM; // Now, set e->env_pgdir and initialize the page directory. // // Hint: // - The VA space of all envs is identical above UTOP // (except at UVPT, which we've set below). // See inc/memlayout.h for permissions and layout. // Can you use kern_pgdir as a template? Hint: Yes. // (Make sure you got the permissions right in Lab 2.) // - The initial VA below UTOP is empty. // - You do not need to make any more calls to page_alloc. // - Note: In general, pp_ref is not maintained for // physical pages mapped only above UTOP, but env_pgdir // is an exception -- you need to increment env_pgdir's // pp_ref for env_free to work correctly. // - The functions in kern/pmap.h are handy. // LAB 3: Your code here. p->pp_ref++; e->env_pgdir = (pde_t *)page2kva(p); // we can copy kern part of PDEs from kern_pgdir // no need to allocate more physical memory and map again for (int start = PDX(UTOP); start < NPDENTRIES; start ++) { e->env_pgdir[start] = kern_pgdir[start]; } // UVPT maps the env's own page table read-only. // Permissions: kernel R, user R // need to update, if we keep the copy from kern_pgdir, // it will point to kern_pgdir itself, not env_pgdir e->env_pgdir[PDX(UVPT)] = PADDR(e->env_pgdir) | PTE_P | PTE_U; return 0; } // // Allocates and initializes a new environment. // On success, the new environment is stored in *newenv_store. // // Returns 0 on success, < 0 on failure. Errors include: // -E_NO_FREE_ENV if all NENV environments are allocated // -E_NO_MEM on memory exhaustion // int env_alloc(struct Env **newenv_store, envid_t parent_id) { int32_t generation; int r; struct Env *e; if (!(e = env_free_list)) return -E_NO_FREE_ENV; // Allocate and set up the page directory for this environment. if ((r = env_setup_vm(e)) < 0) return r; // Generate an env_id for this environment. generation = (e->env_id + (1 << ENVGENSHIFT)) & ~(NENV - 1); if (generation <= 0) // Don't create a negative env_id. generation = 1 << ENVGENSHIFT; e->env_id = generation | (e - envs); // Set the basic status variables. e->env_parent_id = parent_id; e->env_type = ENV_TYPE_USER; e->env_status = ENV_RUNNABLE; e->env_runs = 0; // Clear out all the saved register state, // to prevent the register values // of a prior environment inhabiting this Env structure // from "leaking" into our new environment. memset(&e->env_tf, 0, sizeof(e->env_tf)); // Set up appropriate initial values for the segment registers. // GD_UD is the user data segment selector in the GDT, and // GD_UT is the user text segment selector (see inc/memlayout.h). // The low 2 bits of each segment register contains the // Requestor Privilege Level (RPL); 3 means user mode. When // we switch privilege levels, the hardware does various // checks involving the RPL and the Descriptor Privilege Level // (DPL) stored in the descriptors themselves. e->env_tf.tf_ds = GD_UD | 3; e->env_tf.tf_es = GD_UD | 3; e->env_tf.tf_ss = GD_UD | 3; e->env_tf.tf_esp = USTACKTOP; e->env_tf.tf_cs = GD_UT | 3; // You will set e->env_tf.tf_eip later. // Enable interrupts while in user mode. // LAB 4: Your code here. e->env_tf.tf_eflags |= FL_IF; // Clear the page fault handler until user installs one. e->env_pgfault_upcall = 0; // Also clear the IPC receiving flag. e->env_ipc_recving = 0; // commit the allocation env_free_list = e->env_link; *newenv_store = e; // slient this line // cprintf("[%08x] new env %08x\n", curenv ? curenv->env_id : 0, e->env_id); return 0; } // // Allocate len bytes of physical memory for environment env, // and map it at virtual address va in the environment's address space. // Does not zero or otherwise initialize the mapped pages in any way. // Pages should be writable by user and kernel. // Panic if any allocation attempt fails. // static void region_alloc(struct Env *e, void *va, size_t len) { // LAB 3: Your code here. // (But only if you need it for load_icode.) // // Hint: It is easier to use region_alloc if the caller can pass // 'va' and 'len' values that are not page-aligned. // You should round va down, and round (va + len) up. // (Watch out for corner-cases!) // page that contains va & va + len uint32_t start = (uint32_t)ROUNDDOWN(va, PGSIZE); uint32_t end = (uint32_t)ROUNDUP(va + len, PGSIZE); for (uint32_t va = start; va < end; va += PGSIZE) { pte_t *pgtbl = pgdir_walk(e->env_pgdir, (const void *)va, 1); struct PageInfo *pg_info = NULL; if (pgtbl && !(*pgtbl & PTE_P)) // for already-mapped page, we don't init it in any way pg_info = page_alloc(ALLOC_ZERO); if (pg_info == NULL) panic("page_alloc: %e", -E_NO_MEM); // previously I only did the update of page table entry // but I ignored the reference count of physical pages, // so when a process fork child processes, the page that // contains the code & data will be freed and then re-alloc, // which will cause undefined behaviors among processes running page_insert(e->env_pgdir, pg_info, (void *)va, PTE_U | PTE_W); } } // // Set up the initial program binary, stack, and processor flags // for a user process. // This function is ONLY called during kernel initialization, // before running the first user-mode environment. // // This function loads all loadable segments from the ELF binary image // into the environment's user memory, starting at the appropriate // virtual addresses indicated in the ELF program header. // At the same time it clears to zero any portions of these segments // that are marked in the program header as being mapped // but not actually present in the ELF file - i.e., the program's bss section. // // All this is very similar to what our boot loader does, except the boot // loader also needs to read the code from disk. Take a look at // boot/main.c to get ideas. // // Finally, this function maps one page for the program's initial stack. // // load_icode panics if it encounters problems. // - How might load_icode fail? What might be wrong with the given input? // static void load_icode(struct Env *e, uint8_t *binary) { // Hints: // Load each program segment into virtual memory // at the address specified in the ELF segment header. // You should only load segments with ph->p_type == ELF_PROG_LOAD. // Each segment's virtual address can be found in ph->p_va // and its size in memory can be found in ph->p_memsz. // The ph->p_filesz bytes from the ELF binary, starting at // 'binary + ph->p_offset', should be copied to virtual address // ph->p_va. Any remaining memory bytes should be cleared to zero. // (The ELF header should have ph->p_filesz <= ph->p_memsz.) // Use functions from the previous lab to allocate and map pages. // // All page protection bits should be user read/write for now. // ELF segments are not necessarily page-aligned, but you can // assume for this function that no two segments will touch // the same virtual page. // // You may find a function like region_alloc useful. // // Loading the segments is much simpler if you can move data // directly into the virtual addresses stored in the ELF binary. // So which page directory should be in force during // this function? // // You must also do something with the program's entry point, // to make sure that the environment starts executing there. // What? (See env_run() and env_pop_tf() below.) // LAB 3: Your code here. struct Elf *elf_header = (struct Elf *)binary; if (elf_header->e_magic != ELF_MAGIC) panic("invalid elf file"); struct Proghdr *ph, *eph; ph = (struct Proghdr *)((uint8_t *)elf_header + elf_header->e_phoff); eph = ph + elf_header->e_phnum; for (; ph < eph; ph++) { if (ph->p_type == ELF_PROG_LOAD && ph->p_filesz <= ph->p_memsz) { region_alloc(e, (void *)ph->p_va, ph->p_memsz); lcr3(PADDR(e->env_pgdir)); memmove((void *)ph->p_va, (void*)(binary + ph->p_offset), ph->p_filesz); lcr3(PADDR(kern_pgdir)); } } e->env_tf.tf_eip = elf_header->e_entry; // Now map one page for the program's initial stack // at virtual address USTACKTOP - PGSIZE. // LAB 3: Your code here. struct PageInfo *stack_page = page_alloc(ALLOC_ZERO); if (page_insert(e->env_pgdir, stack_page, (void *)(USTACKTOP - PGSIZE), PTE_U | PTE_W) != 0) { panic("alloc user stack"); } } // // Allocates a new env with env_alloc, loads the named elf // binary into it with load_icode, and sets its env_type. // This function is ONLY called during kernel initialization, // before running the first user-mode environment. // The new env's parent ID is set to 0. // void env_create(uint8_t *binary, enum EnvType type) { // LAB 3: Your code here. // If this is the file server (type == ENV_TYPE_FS) give it I/O privileges. // LAB 5: Your code here. struct Env *new_env; if (env_alloc(&new_env, 0) != 0) panic("env_alloc"); load_icode(new_env, binary); if (type == ENV_TYPE_FS) new_env->env_tf.tf_eflags |= FL_IOPL_3; new_env->env_type = type; } // // Frees env e and all memory it uses. // void env_free(struct Env *e) { pte_t *pt; uint32_t pdeno, pteno; physaddr_t pa; // If freeing the current environment, switch to kern_pgdir // before freeing the page directory, just in case the page // gets reused. if (e == curenv) lcr3(PADDR(kern_pgdir)); // Note the environment's demise. // cprintf("[%08x] free env %08x\n", curenv ? curenv->env_id : 0, e->env_id); // Flush all mapped pages in the user portion of the address space static_assert(UTOP % PTSIZE == 0); for (pdeno = 0; pdeno < PDX(UTOP); pdeno++) { // only look at mapped page tables if (!(e->env_pgdir[pdeno] & PTE_P)) continue; // find the pa and va of the page table pa = PTE_ADDR(e->env_pgdir[pdeno]); pt = (pte_t*) KADDR(pa); // unmap all PTEs in this page table for (pteno = 0; pteno <= PTX(~0); pteno++) { if (pt[pteno] & PTE_P) page_remove(e->env_pgdir, PGADDR(pdeno, pteno, 0)); } // free the page table itself e->env_pgdir[pdeno] = 0; page_decref(pa2page(pa)); } // free the page directory pa = PADDR(e->env_pgdir); e->env_pgdir = 0; page_decref(pa2page(pa)); // return the environment to the free list e->env_status = ENV_FREE; e->env_link = env_free_list; env_free_list = e; } // // Frees environment e. // If e was the current env, then runs a new environment (and does not return // to the caller). // void env_destroy(struct Env *e) { // If e is currently running on other CPUs, we change its state to // ENV_DYING. A zombie environment will be freed the next time // it traps to the kernel. if (e->env_status == ENV_RUNNING && curenv != e) { e->env_status = ENV_DYING; return; } env_free(e); if (curenv == e) { curenv = NULL; sched_yield(); } } // // Restores the register values in the Trapframe with the 'iret' instruction. // This exits the kernel and starts executing some environment's code. // // This function does not return. // void env_pop_tf(struct Trapframe *tf) { // Record the CPU we are running on for user-space debugging curenv->env_cpunum = cpunum(); asm volatile( "\tmovl %0,%%esp\n" "\tpopal\n" "\tpopl %%es\n" "\tpopl %%ds\n" "\taddl $0x8,%%esp\n" /* skip tf_trapno and tf_errcode */ "\tiret\n" : : "g" (tf) : "memory"); panic("iret failed"); /* mostly to placate the compiler */ } // // Context switch from curenv to env e. // Note: if this is the first call to env_run, curenv is NULL. // // This function does not return. // void env_run(struct Env *e) { // Step 1: If this is a context switch (a new environment is running): // 1. Set the current environment (if any) back to // ENV_RUNNABLE if it is ENV_RUNNING (think about // what other states it can be in), // 2. Set 'curenv' to the new environment, // 3. Set its status to ENV_RUNNING, // 4. Update its 'env_runs' counter, // 5. Use lcr3() to switch to its address space. // Step 2: Use env_pop_tf() to restore the environment's // registers and drop into user mode in the // environment. // Hint: This function loads the new environment's state from // e->env_tf. Go back through the code you wrote above // and make sure you have set the relevant parts of // e->env_tf to sensible values. // LAB 3: Your code here. if (curenv != NULL && curenv != e) { if (curenv->env_status == ENV_RUNNING) curenv->env_status = ENV_RUNNABLE; } curenv = e; curenv->env_status = ENV_RUNNING; curenv->env_runs ++; lcr3(PADDR(curenv->env_pgdir)); unlock_kernel(); env_pop_tf(&(curenv->env_tf)); }
Direct OneDrive
env.c
Open the file inline when the browser can handle it, otherwise drop back to a direct download.