uboot 自拷贝运行流程关键代码理解

_main ; CODE XREF: save_boot_params_ret+38↑p

.text_rest:80000FA0 MOV R0, #0x84000000

.text_rest:80000FA4 BIC R0, R0, #7 ; top

.text_rest:80000FA8 MOV SP, R0

.text_rest:80000FAC BL board_init_f_alloc_reserve

.text_rest:80000FB0 MOV SP, R0

.text_rest:80000FB4 MOV R9, R0

.text_rest:80000FB8 BL board_init_f_init_reserve

.text_rest:80000FBC MOV R0, #0 ; boot_flags

.text_rest:80000FC0 BL board_init_f

.text_rest:80000FC4 LDR R0, [R9,#0x48]

.text_rest:80000FC8 BIC R0, R0, #7

.text_rest:80000FCC MOV SP, R0

.text_rest:80000FD0 LDR R9, [R9]

.text_rest:80000FD4 SUB R9, R9, #0xD8

.text_rest:80000FD8 ADR LR, here ;获取标号here的绝对运行pc值 80000FEC

.text_rest:80000FDC LDR R0, [R9,#0x4C] ;取重定向的固定偏移量 比如10000000

.text_rest:80000FE0 ADD LR, LR, R0 ;加上

.text_rest:80000FE4 LDR R0, [R9,#0x38]

.text_rest:80000FE8 B relocate_code

.text_rest:80000FE8 ; End of function _main

.text_rest:80000FE8 这个地方要注意，上面的代码是在80000xxx位置跑的，而下面的代码却在 90000xxx 的位置跑

关键就在 relocate_code，relocate_code这个函数把从80000000开始的代码拷贝到了90000000

开始的位置，当然也包括现在描述的这个部分。并且对 LDR PC, =xxx 这样的指令做了重新偏移映射

LR在 relocate_code 之前已经计算好是 90000xxx的位置，BX LR 就跳到新地址去运行了。

.text_rest:80000FEC

.text_rest:80000FEC ; =============== S U B R O U T I N E =======================================

.text_rest:80000FEC

.text_rest:80000FEC

.text_rest:80000FEC here ; DATA XREF: _main+38↑o

.text_rest:80000FEC BL relocate_vectors

.text_rest:80000FF0 BL c_runtime_cpu_setup

.text_rest:80000FF4 LDR R0, =__rel_dyn_start

.text_rest:80000FF8 LDR R3, =__bss_end

.text_rest:80000FFC MOV R1, #0

.text_rest:80001000 SUBS R2, R3, R0

.text_rest:80001004 BL memset

.text_rest:80001008 BL coloured_LED_init

.text_rest:8000100C BL red_led_on

.text_rest:80001010 MOV R0, R9 ; new_gd

.text_rest:80001014 LDR R1, [R9,#0x38] ; dest_addr

.text_rest:80001018 LDR PC, =board_init_r

.text_rest:80001018 ; End of function here

.text_rest:80001018

.text_rest:80001018 ; ---------------------------------------------------------------------------

.text_rest:8000101C off_8000101C DCD __rel_dyn_start ; DATA XREF: here+8↑r

.text_rest:80001020 off_80001020 DCD __bss_end ; DATA XREF: here+C↑r

.text_rest:80001024 off_80001024 DCD board_init_r ; DATA XREF: here+2C↑r

relocate_code ; CODE XREF: _main+48↑j

.text_rest:800014D8 LDR R1, =__image_copy_start

.text_rest:800014DC SUBS R4, R0, R1

.text_rest:800014E0 BEQ relocate_done

.text_rest:800014E4 LDR R2, =__rel_dyn_start

.text_rest:800014E8

.text_rest:800014E8 copy_loop ; CODE XREF: relocate_code+1C↓j

.text_rest:800014E8 LDM R1!, {R10,R11}

.text_rest:800014EC STM R0!, {R10,R11}

.text_rest:800014F0 CMP R1, R2

.text_rest:800014F4 BCC copy_loop

.text_rest:800014F8 LDR R2, =__rel_dyn_start

.text_rest:800014FC LDR R3, =(seqNumFlag+0x38DC)

.text_rest:80001500

.text_rest:80001500 fixloop ; CODE XREF: relocate_code+4C↓j

.text_rest:80001500 LDM R2!, {R0,R1}

.text_rest:80001504 AND R1, R1, #0xFF

.text_rest:80001508 CMP R1, #0x17

.text_rest:8000150C BNE fixnext

.text_rest:80001510 ADD R0, R0, R4

.text_rest:80001514 LDR R1, [R0]

.text_rest:80001518 ADD R1, R1, R4

.text_rest:8000151C STR R1, [R0]

.text_rest:80001520

.text_rest:80001520 fixnext ; CODE XREF: relocate_code+34↑j

.text_rest:80001520 CMP R2, R3

.text_rest:80001524 BCC fixloop

.text_rest:80001528

.text_rest:80001528 relocate_done ; CODE XREF: relocate_code+8↑j

.text_rest:80001528 BX LR

.text_rest:80001528 ; End of function relocate_code