linux内核vmlinux启动过程中是如何调用到__arm920_setup函数的（2） address, linux, return, 如何, 程序

yuyang911220

最后的这句话（红色部分对应）就是返回到LR所指的地方继续运行，lr中方的是什么呢？
第3句adr lr, __enable_mmu @ return (PIC) address                      3中不做好准备了么，此时程序就跳转到__enable_mmu处继续执行。
找到标号__enable_mmu 对应的段：看最后一句，
__enable_mmu:
#ifdef CONFIG_ALIGNMENT_TRAP
orr r0, r0, #CR_A
#else
bic r0, r0, #CR_A
#endif
#ifdef CONFIG_CPU_DCACHE_DISABLE
bic r0, r0, #CR_C
#endif
#ifdef CONFIG_CPU_BPREDICT_DISABLE
bic r0, r0, #CR_Z
#endif
#ifdef CONFIG_CPU_ICACHE_DISABLE
bic r0, r0, #CR_I
#endif
mov r5, #(domain_val(DOMAIN_USER, DOMAIN_MANAGER) | \
      domain_val(DOMAIN_KERNEL, DOMAIN_MANAGER) | \
      domain_val(DOMAIN_TABLE, DOMAIN_MANAGER) | \
      domain_val(DOMAIN_IO, DOMAIN_CLIENT))
mcr p15, 0, r5, c3, c0, 0 @ load domain access register
mcr p15, 0, r4, c2, c0, 0 @ load page table pointer
b __turn_mmu_on
/*
* Enable the MMU.  This completely changes the structure of the visible
* memory space.  You will not be able to trace execution through this.
* If you have an enquiry about this, *please* check the linux-arm-kernel
* mailing list archives BEFORE sending another post to the list.
*
*  r0  = cp#15 control register
*  r13 = *virtual* address to jump to upon completion
*
* other registers depend on the function called upon completion
*/
.align 5
.type __turn_mmu_on, %function
__turn_mmu_on:
mov r0, r0
mcr p15, 0, r0, c1, c0, 0 @ write control reg
mrc p15, 0, r3, c0, c0, 0 @ read id reg
mov r3, r3
mov r3, r3
mov pc, r13
红色部分的含义就是程序跳转到r13所指的地方继续运行。r3指到哪里去了呢，第1句ldr r13, __switch_data @ address to jump to after      1  中不早就准备好了么，r13指向了__switch_data处。
于是程序跳转到__switch_data处继续执行。
找到__switch_data标号处：
__switch_data:
.long __mmap_switched
.long __data_loc @ r4
.long __data_start @ r5
.long __bss_start @ r6
.long _end @ r7
.long processor_id @ r4
.long __machine_arch_type @ r5
.long cr_alignment @ r6
.long init_thread_union + THREAD_START_SP @ sp
/*
* The following fragment of code is executed with the MMU on in MMU mode,
* and uses absolute addresses; this is not position independent.
*
*  r0  = cp#15 control register
*  r1  = machine ID
*  r9  = processor ID
*/
.type __mmap_switched, %function
__mmap_switched:
adr r3, __switch_data + 4
ldmia r3!, {r4, r5, r6, r7}
cmp r4, r5 @ Copy data segment if needed
1: cmpne r5, r6
ldrne fp, [r4], #4
strne fp, [r5], #4
bne 1b
mov fp, #0 @ Clear BSS (and zero fp)
1: cmp r6, r7
strcc fp, [r6],#4
bcc 1b
ldmia r3, {r4, r5, r6, sp}
str r9, [r4] @ Save processor ID
str r1, [r5] @ Save machine type
bic r4, r0, #CR_A @ Clear 'A' bit
stmia r6, {r0, r4} @ Save control register values
b start_kernel
发现程序在执行__mmap_switched后最终调用到了start_kernel函数，开始了C语言的阶段。
大体调用过程应该是这个样子的，希望对你们理解内核的启动过程有所帮助！个别地方描述的有点不准确，希望多多指正，共同探讨，现在才感觉到把自己的思想描述出来是多么困难的一件事了，