_main 函数中,调用完 relocate_code 函数,即执行了uboot重定位后,开始执行relocate_vectors 函数。
本文学习 relocate_vectors 函数,uboot的重定位中断向量表。
_main 函数在 uboot的 /arch/arm/lib/crt0.S 文件中。如下:
b relocate_code
here:
/*
* now relocate vectors
*/
bl relocate_vectors
函数 relocate_vectors 用于重定位向量表,此函数定义在文件 relocate.S 中。
代码如下:
27 ENTRY(relocate_vectors)
28
29 #ifdef CONFIG_CPU_V7M
30 /*
31 * On ARMv7-M we only have to write the new vector address
32 * to VTOR register.
33 */
34 ldr r0, [r9, #GD_RELOCADDR] /* r0 = gd->relocaddr */
35 ldr r1, =V7M_SCB_BASE
36 str r0, [r1, V7M_SCB_VTOR]
37 #else
38 #ifdef CONFIG_HAS_VBAR
39 /*
40 * If the ARM processor has the security extensions,
41 * use VBAR to relocate the exception vectors.
42 */
43 ldr r0, [r9, #GD_RELOCADDR] /* r0 = gd->relocaddr */
44 mcr p15, 0, r0, c12, c0, 0 /* Set VBAR */
45 #else
46 /*
47 * Copy the relocated exception vectors to the
48 * correct address
49 * CP15 c1 V bit gives us the location of the vectors:
50 * 0x00000000 or 0xFFFF0000.
51 */
52 ldr r0, [r9, #GD_RELOCADDR] /* r0 = gd->relocaddr */
53 mrc p15, 0, r2, c1, c0, 0 /* V bit (bit[13]) in CP15 c1 */
54 ands r2, r2, #(1 << 13)
55 ldreq r1, =0x00000000 /* If V=0 */
56 ldrne r1, =0xFFFF0000 /* If V=1 */
57 ldmia r0!, {r2-r8,r10}
58 stmia r1!, {r2-r8,r10}
59 ldmia r0!, {r2-r8,r10}
60 stmia r1!, {r2-r8,r10}
61 #endif
62 #endif
63 bx lr
64
65 ENDPROC(relocate_vectors)
relocate_vectors 函数可以看出,对于 IMX6ULL芯片而言,因为属于 Cortex-A7架构,所以,这个函数中只执行了两行:
#ifdef CONFIG_HAS_VBAR
39 /*
40 * If the ARM processor has the security extensions,
41 * use VBAR to relocate the exception vectors.
42 */
43 ldr r0, [r9, #GD_RELOCADDR] /* r0 = gd->relocaddr */
44 mcr p15, 0, r0, c12, c0, 0 /* Set VBAR */
relocate_vectors 函数主要做的事:设置 VBAR寄存器为重定位后的中断向量表起始地址。