TEE/REE系统切换时ATF的寄存器的保存和恢复

程序员文章站 2022-07-13 16:11:59

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ATF点滴

1、设置运行时栈SP
2、寄存器的保存和恢复的实现
3、寄存器的保存和恢复的使用场景

1、设置运行时栈SP

bl31_entrypoint—>el3_entrypoint_common---->plat_set_my_stack—>platform_set_stack—>platform_get_stack

动态找到该cpu的栈地址

func platform_set_stack
	mov x9, x30 // lr
	bl  platform_get_stack
	mov sp, x0
	ret x9
endfunc platform_set_stack

/*
 * This macro calculates the base address of the current CPU's MP stack
 * using the plat_my_core_pos() index, the name of the stack storage
 * and the size of each stack
 * Out: X0 = physical address of stack base
 * Clobber: X30, X1, X2
 */
.macro get_my_mp_stack _name, _size
bl  plat_my_core_pos
ldr x2, =(\_name + \_size)
mov x1, #\_size
madd x

补充madd指令小知识
MADD Rd, Rn, Rm, Ra => Rd = Ra + Rn*Rm

2、寄存器的保存和恢复的实现

在tee/ree系统切换时，需要保存和恢复一些寄存器，这些寄存器包含：

general registers
system registers
fp registers
EL3_register

函数的实现
例如general registers的保存和恢复，如X0其实是保存在了当前sp + CTX_GPREGS_OFFSET + CTX_GPREG_X0处，也就是保存在了栈中

func save_gp_registers
	stp	x0, x1, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X0]
	stp	x2, x3, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X2]
	stp	x4, x5, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X4]
	stp	x6, x7, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X6]
	stp	x8, x9, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X8]
	stp	x10, x11, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X10]
	stp	x12, x13, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X12]
	stp	x14, x15, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X14]
	stp	x16, x17, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X16]
	stp	x18, x19, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X18]
	stp	x20, x21, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X20]
	stp	x22, x23, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X22]
	stp	x24, x25, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X24]
	stp	x26, x27, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X26]
	stp	x28, x29, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X28]
	mrs	x18, sp_el0
	str	x18, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_SP_EL0]
	ret
endfunc save_gp_registers
func restore_gp_registers_callee_eret
	ldp	x4, x5, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X4]
	ldp	x6, x7, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X6]
	ldp	x8, x9, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X8]
	ldp	x10, x11, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X10]
	ldp	x12, x13, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X12]
	ldp	x14, x15, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X14]
	ldp	x18, x19, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X18]
	ldp	x20, x21, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X20]
	ldp	x22, x23, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X22]
	ldp	x24, x25, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X24]
	ldp	x26, x27, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X26]
	ldp	x28, x29, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X28]
	ldp	 x30, x17, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_LR]
	msr	sp_el0, x17
	ldp	x16, x17, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X16]
	eret
endfunc	restore_gp_registers_callee_eret