本文分析基于Linux 0.11內核,轉載請標明出處, http://blog.csdn.net/yming0221/archive/2011/06/01/6459119.aspx
在main.c的程序中,當設備初始化完畢后,程序將從內核模式切換到用戶模式,也就是所說的任務0,執行fork()函數(該函數使用內嵌的匯
編,防止函數調用弄亂堆棧,造成寫時復制COPY_ON_WRITE)切換到用戶堆棧并執行任務0使用iret指令,首先將有關的值壓入堆棧,然后執
行iret指令。將剛剛壓入對堆棧的數據根據標志位彈入相應的寄存器。
執行iret前的堆棧如下:
一下這段話引用自 http://faydoc.tripod.com/cpu/iret.htm
In Protected Mode, the action of the IRET instruction depends on the settings of the NT (nested task) and VM flags in the EFLAGS register and the VM flag in the EFLAGS image stored on the current stack. Depending on the setting of these flags, the processor performs the following types of interrupt returns:
- Return from virtual-8086 mode.
- Return to virtual-8086 mode.
- Intra-privilege level return.
- Inter-privilege level return.
- Return from nested task (task switch).
If the NT flag (EFLAGS register) is cleared, the IRET instruction performs a far return from the interrupt procedure, without a task switch. The code segment being returned to must be equally or less privileged than the interrupt handler routine (as indicated by the RPL field of the code segment selector popped from the stack). As with a real-address mode interrupt return, the IRET instruction pops the return instruction pointer, return code segment selector, and EFLAGS image from the stack to the EIP, CS, and EFLAGS registers, respectively, and then resumes execution of the interrupted program or procedure. If the return is to another privilege level, the IRET instruction also pops the stack pointer and SS from the stack, before resuming program execution. If the return is to virtual-8086 mode, the processor also pops the data segment registers from the stack.
-----------------------------------
由于在sched_init()中已經設置了標志寄存器中的vm標志為0,所以iret掉用后不會發生任務切換,而是繼續執行EIP指向的指令故繼續執行
1標號的代碼,開始執行任務0,任務0的堆棧段選擇符為0x17,在sched_init()中已設置了任務0 的任務描述符和局部描述符為INIT_TASK
更多文章、技術交流、商務合作、聯系博主
微信掃碼或搜索:z360901061

微信掃一掃加我為好友
QQ號聯系: 360901061
您的支持是博主寫作最大的動力,如果您喜歡我的文章,感覺我的文章對您有幫助,請用微信掃描下面二維碼支持博主2元、5元、10元、20元等您想捐的金額吧,狠狠點擊下面給點支持吧,站長非常感激您!手機微信長按不能支付解決辦法:請將微信支付二維碼保存到相冊,切換到微信,然后點擊微信右上角掃一掃功能,選擇支付二維碼完成支付。
【本文對您有幫助就好】元
