/*
 * void relocate_code(addr_moni)
 *
 * This function relocates the monitor code.
 * x0 holds the destination address.
 */
ENTRY(relocate_code)
	stp	x29, x30, [sp, #-32]!	/* create a stack frame */
	mov	x29, sp
	str	x0, [sp, #16]
	/*
	 * Copy u-boot from flash to RAM
	 * __image_copy_start = _TEXT_BASE = CONFIG_SYS_TEXT_BASE = 0x80000, 初始加载地址
	 */
	adrp	x1, __image_copy_start		/* x1 <- address bits [31:12] */
	add	x1, x1, :lo12:__image_copy_start/* x1 <- address bits [11:00] */
	subs	x9, x0, x1			/* x9 <- Run to copy offset, X9 = 重定位前后地址的offset */
	b.eq	relocate_done			/* skip relocation */
	/*
	 * Don't ldr x1, __image_copy_start here, since if the code is already
	 * running at an address other than it was linked to, that instruction
	 * will load the relocated value of __image_copy_start. To
	 * correctly apply relocations, we need to know the linked value.
	 *
	 * Linked &__image_copy_start, which we know was at
	 * CONFIG_SYS_TEXT_BASE, which is stored in _TEXT_BASE, as a non-
	 * relocated value, since it isn't a symbol reference.
	 */
	ldr	x1, _TEXT_BASE		/* x1 <- Linked &__image_copy_start */
	subs	x9, x0, x1		/* x9 <- Link to copy offset, X9 = 重定位前后地址的offset */

	adrp	x1, __image_copy_start		/* x1 <- address bits [31:12] */
	add	x1, x1, :lo12:__image_copy_start/* x1 <- address bits [11:00] */
	adrp	x2, __image_copy_end		/* x2 <- address bits [31:12] */
	add	x2, x2, :lo12:__image_copy_end	/* x2 <- address bits [11:00] */
copy_loop:
	ldp	x10, x11, [x1], #16	/* copy from source address [x1] */
	stp	x10, x11, [x0], #16	/* copy to   target address [x0] */
	cmp	x1, x2			/* until source end address [x2] */
	b.lo	copy_loop
	str	x0, [sp, #24]
	
	/* 上面代码完成__image_copy_start、__image_copy_end之间的代码拷贝，包括text和data段 */
	
	/*
	 * Fix .rela.dyn relocations
	 * rela.dyn里1个LABEL结构是：
	 * 8 Bytes 地址
	 * 8 Bytes 标记
	 * 8 Bytes addend
	 */
	adrp	x2, __rel_dyn_start		/* x2 <- address bits [31:12] */
	add	x2, x2, :lo12:__rel_dyn_start	/* x2 <- address bits [11:00] */
	adrp	x3, __rel_dyn_end		/* x3 <- address bits [31:12] */
	add	x3, x3, :lo12:__rel_dyn_end	/* x3 <- address bits [11:00] */
fixloop:
	ldp	x0, x1, [x2], #16	/* (x0,x1) <- (SRC location, fixup)， X0是label地址，X1存标记 */
	ldr	x4, [x2], #8		/* x4 <- label地址里的值 */
	and	x1, x1, #0xffffffff
	cmp	x1, #R_AARCH64_RELATIVE
	bne	fixnext

	/* relative fix: store addend plus offset at dest location */
	add	x0, x0, x9       
	add	x4, x4, x9
	str	x4, [x0]       /* label值 + offset =  lable里的值(全局变量地址) +offset */
fixnext:
	cmp	x2, x3
	b.lo	fixloop

relocate_done:
	switch_el x1, 3f, 2f, 1f
	bl	hang
3:	mrs	x0, sctlr_el3
	b	0f
2:	mrs	x0, sctlr_el2
	b	0f
1:	mrs	x0, sctlr_el1
0:	tbz	w0, #2, 5f	/* skip flushing cache if disabled */
	tbz	w0, #12, 4f	/* skip invalidating i-cache if disabled */
	ic	iallu		/* i-cache invalidate all */
	isb	sy
4:	ldp	x0, x1, [sp, #16]
	bl	__asm_flush_dcache_range
	bl     __asm_flush_l3_dcache
5:	ldp	x29, x30, [sp],#32
	ret
ENDPROC(relocate_code)

3.5 board_init_r()

3.5.1 init_sequence_r

relocate之后的初始化及主函数，执行init_sequence_r[]里的函数指针。

• initr_trace，初始化并使能u-boot的tracing system，涉及的配置项有CONFIG_TRACE。
• initr_reloc，设置relocation完成的标志。
• initr_caches，使能dcache、icache等，涉及的配置项有CONFIG_ARM。
• initr_reloc_global_data(), 重定位gd相关内容，gd->env_addr，gd->fdt_blob，efi相关初始化
• initr_malloc，malloc有关的初始化
• log_init, log相关初始化
• initr_dm， relocate之后，重新初始化DM，涉及的配置项有CONFIG_DM
• board_init，具体的板级初始化，需要由board代码根据需要实现，涉及的配置项有CONFIG_ARM。
• set_cpu_clk_info，Initialize clock framework，涉及的配置项有CONFIG_CLOCKS。
• efi_memory_init， efi相关初始化
• initr_binman() ?
• initr_dm_devices, CONFIG_TIMER_EARLY决定是否初始化timer
• stdio_init_tables
• serial_initialize
• initr_announce， 打印
• board_early_init_r， CONFIG_BOARD_EARLY_INIT_R控制是否调用，板级实现
• arch_early_init_r，由arch代码实现，涉及的配置项有CONFIG_ARCH_EARLY_INIT_R。
• power_init_board，板级的power init代码，由板级代码实现，例如hold住power。
• initr_flash,initr_nand，initr_onenand，initr_mmc，根据各宏调用各存储设备初始化
• initr_env， 环境变量相关初始化
• initr_secondary_cpu，其他core初始化
• stdio_add_devices，各种输入输出设备的初始化，如LCD driver等
• initr_jumptable ?
• console_init_r
• arch_misc_init, 受CONFIG_ARCH_MISC_INIT控制的arch杂项
• misc_init_r， 受CONFIG_MISC_INIT_R控制
• interrupt_init， 使能中断
• initr_status_led，状态指示LED的初始化，涉及的配置项有CONFIG_STATUS_LED、STATUS_LED_BOOT。
• initr_ethaddr，Ethernet的初始化，涉及的配置项有CONFIG_CMD_NET。
• board_late_init， 由板级代码实现，涉及的配置项有CONFIG_BOARD_LATE_INIT
• initr_net。网络初始化，CONFIG_CMD_NET
• run_main_loop/main_loop，主循环

3.5.2 main_loop

参考

http://www.wowotech.net/u-boot/boot_flow_1.html
https://blog.csdn.net/skyflying2012/article/details/37660265
https://blog.csdn.net/ooonebook/article/details/53047992