文章目錄

• • • • 1、先看kernel調用userspace所需的的參數
      • 2、先看kernel mode切換user mode的寄存器行為

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我們以optee為例，看下kernel space調用user space時有哪些硬件行為

1、先看kernel調用userspace所需的的參數

• 函數入庫
• session
• 函數參數
• cmd
• usr_stack //該應用程序的棧地址
• enrty_func
• is_32bit //該參數只是在kernel中使用
• panicked
• panic_code

res = thread_enter_user_mode(func, tee_svc_kaddr_to_uref(session),(vaddr_t)usr_params, cmd, usr_stack,utc->entry_func, utc->is_32bit,&utc->ctx.panicked, &utc->ctx.panic_code);uint32_t thread_enter_user_mode(unsigned long a0, unsigned long a1,unsigned long a2, unsigned long a3, unsigned long user_sp,unsigned long entry_func, bool is_32bit,uint32_t *exit_status0, uint32_t *exit_status1) {uint32_t spsr;tee_ta_update_session_utime_resume();if (!get_spsr(is_32bit, entry_func, &spsr)) {*exit_status0 = 1; /* panic */*exit_status1 = 0xbadbadba;return 0;}return __thread_enter_user_mode(a0, a1, a2, a3, user_sp, entry_func,spsr, exit_status0, exit_status1); }

2、先看kernel mode切換user mode的寄存器行為

將usr_stack地址，同時寫入到了x13(R13/sp_usr)、和SP_EL0， 也就是在此處，程序并不需要知道你的userspace是32位或64位

FUNC __thread_enter_user_mode , :ldr x8, [sp]/** Create the and fill in the struct thread_user_mode_rec*/sub sp, sp, #THREAD_USER_MODE_REC_SIZEstore_xregs sp, THREAD_USER_MODE_REC_EXIT_STATUS0_PTR, 7, 8store_xregs sp, THREAD_USER_MODE_REC_X19, 19, 30/** Switch to SP_EL1* Disable exceptions* Save kern sp in x19*/msr daifset, #DAIFBIT_ALLmov x19, spmsr spsel, #1/** Save the kernel stack pointer in the thread context*//* get pointer to current thread context */get_thread_ctx sp, 21, 20, 22/** Save kernel stack pointer to ensure that el0_svc() uses* correct stack pointer*/str x19, [x21, #THREAD_CTX_KERN_SP]/** Initialize SPSR, ELR_EL1, and SP_EL0 to enter user mode*/msr spsr_el1, x6/* Set user sp */mov x13, x4 /* Used when running TA in Aarch32 */msr sp_el0, x4 /* Used when running TA in Aarch64 *//* Set user function */msr elr_el1, x5/* Set frame pointer (user stack can't be unwound past this point) */mov x29, #0/* Jump into user mode */store_xregs sp, THREAD_CORE_LOCAL_X0, 0, 1b eret_to_el0 END_FUNC __thread_enter_user_mode

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