ATF点滴
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
3、寄存器的保存和恢复的使用场景
在TEE/REE双系统切换的时候，会先保存当前系统的general registers、system registers，然后再恢复目标系统的general registers、system registers. 具体的操作流程如下图所示