九、uboot 代码流程分析---relloc_code

　　执行完 board_init_f 后，重新跳转回 _main 中执行。

10.1 relloc_code 前

10.1.1 gd 设置

　　在调用board_init_f()完成板卡与全局结构体变量 gd 的初始化后将其拷贝到在代码段下重新分配的全局结构体中。接下来进行sp的重新设置，将r9指向重新分配的全局变量gd，然后进行代码的重定位。

    /* 将 sp 指针指向全局gd的gd->start_addr_sp，即栈底 */
    ldr    r0, [r9, #GD_START_ADDR_SP]    /* sp = gd->start_addr_sp */
    bic    r0, r0, #    /* 8-byte alignment for ABI compliance */
    mov    sp, r0
    ldr    r9, [r9, #GD_BD]        /* r9 = gd->bd */
    sub    r9, r9, #GD_SIZE        /* new GD is below bd */

10.1.2 relocate_vectors

　　当执行未 GD 的设置后，跳转到 relocate_vectors 中去执行向量初始化

 adr    lr, here

 here:
 /*
  * now relocate vectors
  */

     bl    relocate_vectors

　　relocate_vectors 主要是进行异常向量表的重定位，将异常向量表拷贝到正确的地址中去，relocate.S (arch\arm\lib)

 ENTRY(relocate_vectors)
     /*
      * Copy the relocated exception vectors to the
      * correct address
      * CP15 c1 V bit gives us the location of the vectors:
      * 0x00000000 or 0xFFFF0000.
      */
     ldr    r0, [r9, #GD_RELOCADDR]    /* r0 = gd->relocaddr */
     mrc    p15, , r2, c1, c0,     /* V bit (bit[13]) in CP15 c1 */
     ands    r2, r2, #( << )
     ldreq    r1, =0x00000000        /* If V=0 */
     ldrne    r1, =0xFFFF0000        /* If V=1 */
     ldmia    r0!, {r2-r8,r10}
     stmia    r1!, {r2-r8,r10}
     ldmia    r0!, {r2-r8,r10}
     stmia    r1!, {r2-r8,r10}
     bx    lr

 ENDPROC(relocate_vectors)

10.1.3  relocate_code

　　紧接着设置重定位的开始和结束地址。设置完成后跳转到 relocate_code（relocate.S） 中执行

     ldr    r0, [r9, #GD_RELOC_OFF]        /* r0 = gd->reloc_off */
     add    lr, lr, r0
     ldr    r0, [r9, #GD_RELOCADDR]        /* r0 = gd->relocaddr */
     b    relocate_code

　　拷贝代码段和动态连接段

 ENTRY(relocate_code)
     ldr    r1, =__image_copy_start    /* r1 <- SRC &__image_copy_start */
     subs    r4, r0, r1        /* r4 <- relocation offset */
     beq    relocate_done        /* skip relocation */
     ldr    r2, =__image_copy_end    /* r2 <- SRC &__image_copy_end */

     /* 拷贝代码到 SDRAM 中去，.__image_copy_start = 0； */
 copy_loop:
     ldmia    r1!, {r10-r11}        /* copy from source address [r1]    */
     stmia    r0!, {r10-r11}        /* copy to   target address [r0]    */
     cmp    r1, r2            /* until source end address [r2]    */
     blo    copy_loop

     /*
      * fix .rel.dyn relocations
      * 重定位 .rel.dyn 段
      */
     ldr    r2, =__rel_dyn_start    /* r2 <- SRC &__rel_dyn_start */
     ldr    r3, =__rel_dyn_end    /* r3 <- SRC &__rel_dyn_end */
 fixloop:
     ldmia    r2!, {r0-r1}        /* (r0,r1) <- (SRC location,fixup) */
     and    r1, r1, #0xff
     cmp    r1, #R_ARM_RELATIVE
     bne    fixnext

     /* relative fix: increase location by offset */
     add    r0, r0, r4
     ldr    r1, [r0]
     add    r1, r1, r4
     str    r1, [r0]
 fixnext:
     cmp    r2, r3
     blo    fixloop

 relocate_done:

     /* ARMv4- don't know bx lr but the assembler fails to see that */

 #ifdef __ARM_ARCH_4__
     mov    pc, lr
 #else
     bx    lr
 #endif

 ENDPROC(relocate_code)

10.1.4 relocate_code 后

　　运行C环境，清理 BSS，执行点灯等操作，然后跳转到 board_init_r 中执行第二阶段初始化

 /* Set up final (full) environment */

     bl    c_runtime_cpu_setup    /* we still call old routine here */
 #endif
 #if !defined(CONFIG_SPL_BUILD) || defined(CONFIG_SPL_FRAMEWORK)
     ldr    r0, =__bss_start    /* this is auto-relocated! */

     /* 清理 BSS */
 #ifdef CONFIG_USE_ARCH_MEMSET
     ldr    r3, =__bss_end        /* this is auto-relocated! */
     mov    r1, #0x00000000        /* prepare zero to clear BSS */

     subs    r2, r3, r0        /* r2 = memset len */
     bl    memset
 #endif

 #if ! defined(CONFIG_SPL_BUILD)
     bl coloured_LED_init
     bl red_led_on
 #endif
     /* call board_init_r(gd_t *id, ulong dest_addr) */
     mov     r0, r9                  /* gd_t */
     ldr    r1, [r9, #GD_RELOCADDR]    /* dest_addr */
     /* call board_init_r */
     ldr    pc, =board_init_r    /* this is auto-relocated! */
     /* we should not return here. */
 #endif