上一篇思路有点乱，又参考了一些资料，随手记录一下。
因为最近用的Xilinx，所以以arm里面的arm7为例：
u-boot的启动过程可以分为两个阶段，分别如下：
第一阶段：
．初始化硬件：如关看门狗、设置时钟、设置SDRAM、初始化NANFLASH等
．如果u-boot的代码量较大，将其u-boot代码加载到SDRAM，即重定位到SDRAM
．设置好栈
．跳转到第二阶段代码入口
第二阶段
．初始化本阶段使用的一些硬件设备
．检测系统内存映射
．将内核从FLASH读取到RAM中
．设置“要传给内核的参数”
．调用内核
第一阶段
程序入口：由u-boot.lds（/arch/arm/cpu/u-boot.lds）的ENTRY(_start)可知，程序的入口在_start。
OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm") //输出格式为elf,32位，小端
OUTPUT_ARCH(arm)
ENTRY(_start)
SECTIONS
{
......
. = 0x00000000;
. = ALIGN(4);
.text :
{
*(.__image_copy_start)
*(.vectors)
CPUDIR/start.o (.text*)
*(.text*)
}入口_start在/arch/arm/lib/vertors.S中，
_start:
#ifdef CONFIG_SYS_DV_NOR_BOOT_CFG
.word CONFIG_SYS_DV_NOR_BOOT_CFG
#endif
ARM_VECTORS
#endif /* !defined(CONFIG_ENABLE_ARM_SOC_BOOT0_HOOK) */文件开始定义了ARM_VECTORS
/*
* A macro to allow insertion of an ARM exception vector either
* for the non-boot0 case or by a boot0-header.
*/
.macro ARM_VECTORS
b reset
ldr pc, _undefined_instruction
ldr pc, _software_interrupt
ldr pc, _prefetch_abort
ldr pc, _data_abort
ldr pc, _not_used
ldr pc, _irq
ldr pc, _fiq
.endm可以看到，从_start入口进去后，立刻跳转到reset中执行。而resert在start.S中。
来到start.S:（/arch/arm/cpu/armv7/start.s）
/*
* armboot - Startup Code for OMAP3530/ARM Cortex CPU-core
*
* Copyright (c) 2004 Texas Instruments <[email protected]>
*
* Copyright (c) 2001 Marius Gröger <[email protected]>
* Copyright (c) 2002 Alex Züpke <[email protected]>
* Copyright (c) 2002 Gary Jennejohn <[email protected]>
* Copyright (c) 2003 Richard Woodruff <[email protected]>
* Copyright (c) 2003 Kshitij <[email protected]>
* Copyright (c) 2006-2008 Syed Mohammed Khasim <[email protected]>
*
* SPDX-License-Identifier: GPL-2.0+
*/
#include <asm-offsets.h>
#include <config.h>
#include <asm/system.h>
#include <linux/linkage.h>
#include <asm/armv7.h>
/*************************************************************************
*
* Startup Code (reset vector) //真正的启动代码
*
* Do important init only if we don't start from memory!
* Setup memory and board specific bits prior to relocation.
* Relocate armboot to ram. Setup stack.
*
*************************************************************************/
.globl reset
.globl save_boot_params_ret
.type save_boot_params_ret,%function
#ifdef CONFIG_ARMV7_LPAE
.global switch_to_hypervisor_ret
#endif
//（1）单板保存一些重要参数（默认不保存）
reset:
/* Allow the board to save important registers */
b save_boot_params
save_boot_params_ret:
#ifdef CONFIG_ARMV7_LPAE
/*
* check for Hypervisor support
*/
mrc p15, 0, r0, c0, c1, 1 @ read ID_PFR1
and r0, r0, #CPUID_ARM_VIRT_MASK @ mask virtualization bits
cmp r0, #(1 << CPUID_ARM_VIRT_SHIFT)
beq switch_to_hypervisor
switch_to_hypervisor_ret:
#endif
//（2）屏蔽中断
/*
* disable interrupts (FIQ and IRQ), also set the cpu to SVC32 mode,
* except if in HYP mode already
*/
mrs r0, cpsr
and r1, r0, #0x1f @ mask mode bits
teq r1, #0x1a @ test for HYP mode
bicne r0, r0, #0x1f @ clear all mode bits
orrne r0, r0, #0x13 @ set SVC mode
orr r0, r0, #0xc0 @ disable FIQ and IRQ
msr cpsr,r0
/*
* Setup vector:
* (OMAP4 spl TEXT_BASE is not 32 byte aligned.
* Continue to use ROM code vector only in OMAP4 spl)
*/
#if !(defined(CONFIG_OMAP44XX) && defined(CONFIG_SPL_BUILD))
/* Set V=0 in CP15 SCTLR register - for VBAR to point to vector */
mrc p15, 0, r0, c1, c0, 0 @ Read CP15 SCTLR Register
bic r0, #CR_V @ V = 0
mcr p15, 0, r0, c1, c0, 0 @ Write CP15 SCTLR Register
/* Set vector address in CP15 VBAR register */
ldr r0, =_start
mcr p15, 0, r0, c12, c0, 0 @Set VBAR
#endif
//（3）底层相关初始化，然后跳转到_main函数执行。
/* the mask ROM code should have PLL and others stable */
#ifndef CONFIG_SKIP_LOWLEVEL_INIT
bl cpu_init_cp15
#ifndef CONFIG_SKIP_LOWLEVEL_INIT_ONLY
bl cpu_init_crit
#endif
#endif
bl _main
/*------------------------------------------------------------------------------*/
ENTRY(c_runtime_cpu_setup)
/*
* If I-cache is enabled invalidate it
*/
#ifndef CONFIG_SYS_ICACHE_OFF
mcr p15, 0, r0, c7, c5, 0 @ invalidate icache
mcr p15, 0, r0, c7, c10, 4 @ DSB
mcr p15, 0, r0, c7, c5, 4 @ ISB
#endif
bx lr
ENDPROC(c_runtime_cpu_setup)
/*************************************************************************
*
* void save_boot_params(u32 r0, u32 r1, u32 r2, u32 r3)
* __attribute__((weak));
*
* Stack pointer is not yet initialized at this moment
* Don't save anything to stack even if compiled with -O0
*
*************************************************************************/
ENTRY(save_boot_params)
b save_boot_params_ret @ back to my caller
ENDPROC(save_boot_params)
.weak save_boot_params
#ifdef CONFIG_ARMV7_LPAE
ENTRY(switch_to_hypervisor)
b switch_to_hypervisor_ret
ENDPROC(switch_to_hypervisor)
.weak switch_to_hypervisor
#endif
/*************************************************************************
*
* cpu_init_cp15
*
* Setup CP15 registers (cache, MMU, TLBs). The I-cache is turned on unless
* CONFIG_SYS_ICACHE_OFF is defined.
*
*************************************************************************/
ENTRY(cpu_init_cp15)
/*
* Invalidate L1 I/D
*/
mov r0, #0 @ set up for MCR
mcr p15, 0, r0, c8, c7, 0 @ invalidate TLBs
mcr p15, 0, r0, c7, c5, 0 @ invalidate icache
mcr p15, 0, r0, c7, c5, 6 @ invalidate BP array
mcr p15, 0, r0, c7, c10, 4 @ DSB
mcr p15, 0, r0, c7, c5, 4 @ ISB
/*
* disable MMU stuff and caches
*/
mrc p15, 0, r0, c1, c0, 0
bic r0, r0, #0x00002000 @ clear bits 13 (--V-)
bic r0, r0, #0x00000007 @ clear bits 2:0 (-CAM)
orr r0, r0, #0x00000002 @ set bit 1 (--A-) Align
orr r0, r0, #0x00000800 @ set bit 11 (Z---) BTB
#ifdef CONFIG_SYS_ICACHE_OFF
bic r0, r0, #0x00001000 @ clear bit 12 (I) I-cache
#else
orr r0, r0, #0x00001000 @ set bit 12 (I) I-cache
#endif
mcr p15, 0, r0, c1, c0, 0
#ifdef CONFIG_ARM_ERRATA_716044
mrc p15, 0, r0, c1, c0, 0 @ read system control register
orr r0, r0, #1 << 11 @ set bit #11
mcr p15, 0, r0, c1, c0, 0 @ write system control register
#endif
#if (defined(CONFIG_ARM_ERRATA_742230) || defined(CONFIG_ARM_ERRATA_794072))
mrc p15, 0, r0, c15, c0, 1 @ read diagnostic register
orr r0, r0, #1 << 4 @ set bit #4
mcr p15, 0, r0, c15, c0, 1 @ write diagnostic register
#endif
#ifdef CONFIG_ARM_ERRATA_743622
mrc p15, 0, r0, c15, c0, 1 @ read diagnostic register
orr r0, r0, #1 << 6 @ set bit #6
mcr p15, 0, r0, c15, c0, 1 @ write diagnostic register
#endif
#ifdef CONFIG_ARM_ERRATA_751472
mrc p15, 0, r0, c15, c0, 1 @ read diagnostic register
orr r0, r0, #1 << 11 @ set bit #11
mcr p15, 0, r0, c15, c0, 1 @ write diagnostic register
#endif
#ifdef CONFIG_ARM_ERRATA_761320
mrc p15, 0, r0, c15, c0, 1 @ read diagnostic register
orr r0, r0, #1 << 21 @ set bit #21
mcr p15, 0, r0, c15, c0, 1 @ write diagnostic register
#endif
#ifdef CONFIG_ARM_ERRATA_845369
mrc p15, 0, r0, c15, c0, 1 @ read diagnostic register
orr r0, r0, #1 << 22 @ set bit #22
mcr p15, 0, r0, c15, c0, 1 @ write diagnostic register
#endif
mov r5, lr @ Store my Caller
mrc p15, 0, r1, c0, c0, 0 @ r1 has Read Main ID Register (MIDR)
mov r3, r1, lsr #20 @ get variant field
and r3, r3, #0xf @ r3 has CPU variant
and r4, r1, #0xf @ r4 has CPU revision
mov r2, r3, lsl #4 @ shift variant field for combined value
orr r2, r4, r2 @ r2 has combined CPU variant + revision
#ifdef CONFIG_ARM_ERRATA_798870
cmp r2, #0x30 @ Applies to lower than R3p0
bge skip_errata_798870 @ skip if not affected rev
cmp r2, #0x20 @ Applies to including and above R2p0
blt skip_errata_798870 @ skip if not affected rev
mrc p15, 1, r0, c15, c0, 0 @ read l2 aux ctrl reg
orr r0, r0, #1 << 7 @ Enable hazard-detect timeout
push {r1-r5} @ Save the cpu info registers
bl v7_arch_cp15_set_l2aux_ctrl
isb @ Recommended ISB after l2actlr update
pop {r1-r5} @ Restore the cpu info - fall through
skip_errata_798870:
#endif
#ifdef CONFIG_ARM_ERRATA_801819
cmp r2, #0x24 @ Applies to lt including R2p4
bgt skip_errata_801819 @ skip if not affected rev
cmp r2, #0x20 @ Applies to including and above R2p0
blt skip_errata_801819 @ skip if not affected rev
mrc p15, 0, r0, c0, c0, 6 @ pick up REVIDR reg
and r0, r0, #1 << 3 @ check REVIDR[3]
cmp r0, #1 << 3
beq skip_errata_801819 @ skip erratum if REVIDR[3] is set
mrc p15, 0, r0, c1, c0, 1 @ read auxilary control register
orr r0, r0, #3 << 27 @ Disables streaming. All write-allocate
@ lines allocate in the L1 or L2 cache.
orr r0, r0, #3 << 25 @ Disables streaming. All write-allocate
@ lines allocate in the L1 cache.
push {r1-r5} @ Save the cpu info registers
bl v7_arch_cp15_set_acr
pop {r1-r5} @ Restore the cpu info - fall through
skip_errata_801819:
#endif
#ifdef CONFIG_ARM_ERRATA_454179
cmp r2, #0x21 @ Only on < r2p1
bge skip_errata_454179
mrc p15, 0, r0, c1, c0, 1 @ Read ACR
orr r0, r0, #(0x3 << 6) @ Set DBSM(BIT7) and IBE(BIT6) bits
push {r1-r5} @ Save the cpu info registers
bl v7_arch_cp15_set_acr
pop {r1-r5} @ Restore the cpu info - fall through
skip_errata_454179:
#endif
#ifdef CONFIG_ARM_ERRATA_430973
cmp r2, #0x21 @ Only on < r2p1
bge skip_errata_430973
mrc p15, 0, r0, c1, c0, 1 @ Read ACR
orr r0, r0, #(0x1 << 6) @ Set IBE bit
push {r1-r5} @ Save the cpu info registers
bl v7_arch_cp15_set_acr
pop {r1-r5} @ Restore the cpu info - fall through
skip_errata_430973:
#endif
#ifdef CONFIG_ARM_ERRATA_621766
cmp r2, #0x21 @ Only on < r2p1
bge skip_errata_621766
mrc p15, 0, r0, c1, c0, 1 @ Read ACR
orr r0, r0, #(0x1 << 5) @ Set L1NEON bit
push {r1-r5} @ Save the cpu info registers
bl v7_arch_cp15_set_acr
pop {r1-r5} @ Restore the cpu info - fall through
skip_errata_621766:
#endif
#ifdef CONFIG_ARM_ERRATA_725233
cmp r2, #0x21 @ Only on < r2p1 (Cortex A8)
bge skip_errata_725233
mrc p15, 1, r0, c9, c0, 2 @ Read L2ACR
orr r0, r0, #(0x1 << 27) @ L2 PLD data forwarding disable
push {r1-r5} @ Save the cpu info registers
bl v7_arch_cp15_set_l2aux_ctrl
pop {r1-r5} @ Restore the cpu info - fall through
skip_errata_725233:
#endif
#ifdef CONFIG_ARM_ERRATA_852421
mrc p15, 0, r0, c15, c0, 1 @ read diagnostic register
orr r0, r0, #1 << 24 @ set bit #24
mcr p15, 0, r0, c15, c0, 1 @ write diagnostic register
#endif
#ifdef CONFIG_ARM_ERRATA_852423
mrc p15, 0, r0, c15, c0, 1 @ read diagnostic register
orr r0, r0, #1 << 12 @ set bit #12
mcr p15, 0, r0, c15, c0, 1 @ write diagnostic register
#endif
mov pc, r5 @ back to my caller
ENDPROC(cpu_init_cp15)
#if !defined(CONFIG_SKIP_LOWLEVEL_INIT) && \
!defined(CONFIG_SKIP_LOWLEVEL_INIT_ONLY)
/*************************************************************************
*
* CPU_init_critical registers
*
* setup important registers
* setup memory timing
*
*************************************************************************/
ENTRY(cpu_init_crit)
/*
* Jump to board specific initialization...
* The Mask ROM will have already initialized
* basic memory. Go here to bump up clock rate and handle
* wake up conditions.
*/
b lowlevel_init @ go setup pll,mux,memory
ENDPROC(cpu_init_crit)
#endif
板级操作
_main函数在/arch/arm/lib/crt0.S中，顺序执行如下操作
ENTRY(_main)
/*
* Set up initial C runtime environment and call board_init_f(0).
*/
#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
ldr r0, =(CONFIG_SPL_STACK)
#else
ldr r0, =(CONFIG_SYS_INIT_SP_ADDR)
#endif
bic r0, r0, #7 /* 8-byte alignment for ABI compliance */
mov sp, r0
bl board_init_f_alloc_reserve
mov sp, r0
/* set up gd here, outside any C code */
mov r9, r0
bl board_init_f_init_reserve
mov r0, #0
bl board_init_f
......
ldr r0, [r9, #GD_RELOCADDR] /* r0 = gd->relocaddr */
b relocate_code
......
#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 */
#if CONFIG_IS_ENABLED(SYS_THUMB_BUILD)
ldr lr, =board_init_r /* this is auto-relocated! */
bx lr
#else
ldr pc, =board_init_r /* this is auto-relocated! */
#endif
/* we should not return here. */
#endif
．board_init_f：\common\board_f.c -> 通过initcall_run_list(init_sequence_f)执行一系列前半部分板级的初始化函数
．relocate_code：\arch\arm\lib\relocate.S -> 重定位u-boot代码，包括复制u-boot代码到SDRAM的过程
．board_init_r：\common\board_r.c -> 通过initcall_run_list(init_sequence_r)执行一系列后半部分的板级初始化函数，并最终调用run_main_loop函数 -> main_loop函数后不再返回，从而完成u-boot第一阶段的启动过程。
以上部分主要是汇编编写。
第二阶段
然后进入main_loop函数中：（common/main.c）
/* We come here after U-Boot is initialised and ready to process commands */
//u-boot启动之后，准备处理命令
void main_loop(void)
{
const char *s;
bootstage_mark_name(BOOTSTAGE_ID_MAIN_LOOP, "main_loop");
#ifdef CONFIG_VERSION_VARIABLE
env_set("ver", version_string); /* set version variable */
#endif /* CONFIG_VERSION_VARIABLE */
cli_init();
run_preboot_environment_command();
#if defined(CONFIG_UPDATE_TFTP)
update_tftp(0UL, NULL, NULL);
#endif /* CONFIG_UPDATE_TFTP */
s = bootdelay_process();
if (cli_process_fdt(&s))
cli_secure_boot_cmd(s);
autoboot_command(s);
cli_loop();
panic("No CLI available");
}其中bootdelay_process函数是为了获取各种bootcmd环境变量：函数位置在本级目录autoboot.c
const char *bootdelay_process(void)
{
char *s;
int bootdelay;
#ifdef CONFIG_BOOTCOUNT_LIMIT
unsigned long bootcount = 0;
unsigned long bootlimit = 0;
#endif /* CONFIG_BOOTCOUNT_LIMIT */
#ifdef CONFIG_BOOTCOUNT_LIMIT
bootcount = bootcount_load();
bootcount++;
bootcount_store(bootcount);
env_set_ulong("bootcount", bootcount);
bootlimit = env_get_ulong("bootlimit", 10, 0);
#endif /* CONFIG_BOOTCOUNT_LIMIT */
s = env_get("bootdelay");
bootdelay = s ? (int)simple_strtol(s, NULL, 10) : CONFIG_BOOTDELAY;
#ifdef CONFIG_OF_CONTROL
bootdelay = fdtdec_get_config_int(gd->fdt_blob, "bootdelay",
bootdelay);
#endif
debug("### main_loop entered: bootdelay=%d\n\n", bootdelay);
#if defined(CONFIG_MENU_SHOW)
bootdelay = menu_show(bootdelay);
#endif
bootretry_init_cmd_timeout();
#ifdef CONFIG_POST
if (gd->flags & GD_FLG_POSTFAIL) {
s = env_get("failbootcmd");
} else
#endif /* CONFIG_POST */
#ifdef CONFIG_BOOTCOUNT_LIMIT
if (bootlimit && (bootcount > bootlimit)) {
printf("Warning: Bootlimit (%u) exceeded. Using altbootcmd.\n",
(unsigned)bootlimit);
s = env_get("altbootcmd");
} else
#endif /* CONFIG_BOOTCOUNT_LIMIT */
s = env_get("bootcmd");
process_fdt_options(gd->fdt_blob);
stored_bootdelay = bootdelay;
return s;
}该函数首先是获取了bootdelay，将其作为按键触发时间限制。函数最后，s时获得了bootcmd变量的数据，然后将其返回。
返回到main_loop函数。接下去执行autoboot_command函数：（文件位置：本级目录autoboot.c）
void autoboot_command(const char *s)
{
debug("### main_loop: bootcmd=\"%s\"\n", s ? s : "<UNDEFINED>");
if (stored_bootdelay != -1 && s && !abortboot(stored_bootdelay)) {
#if defined(CONFIG_AUTOBOOT_KEYED) && !defined(CONFIG_AUTOBOOT_KEYED_CTRLC)
int prev = disable_ctrlc(1); /* disable Control C checking */
#endif
run_command_list(s, -1, 0);
#if defined(CONFIG_AUTOBOOT_KEYED) && !defined(CONFIG_AUTOBOOT_KEYED_CTRLC)
disable_ctrlc(prev); /* restore Control C checking */
#endif
}
#ifdef CONFIG_MENUKEY
if (menukey == CONFIG_MENUKEY) {
s = env_get("menucmd");
if (s)
run_command_list(s, -1, 0);
}
#endif /* CONFIG_MENUKEY */
}该函数首先判断bootdelay,利用if判断：if (stored_bootdelay != -1 && s && !abortboot(stored_bootdelay))，判断中又调用了abortboot函数。
static int abortboot(int bootdelay)
{
int abort = 0;
if (bootdelay >= 0)
abort = __abortboot(bootdelay);
#ifdef CONFIG_SILENT_CONSOLE
if (abort)
gd->flags &= ~GD_FLG_SILENT;
#endif
return abort;
}如果bootdelay大于等于0，跳到__abortboot函数：
static int __abortboot(int bootdelay)
{
int abort = 0;
unsigned long ts;
#ifdef CONFIG_MENUPROMPT
printf(CONFIG_MENUPROMPT);
#else
printf("Hit any key to stop autoboot: %2d ", bootdelay);
#endif
/*
* Check if key already pressed
*/
if (tstc()) { /* we got a key press */
(void) getc(); /* consume input */
puts("\b\b\b 0");
abort = 1; /* don't auto boot */
}
while ((bootdelay > 0) && (!abort)) {
--bootdelay;
/* delay 1000 ms */
ts = get_timer(0);
do {
if (tstc()) { /* we got a key press */
abort = 1; /* don't auto boot */
bootdelay = 0; /* no more delay */
# ifdef CONFIG_MENUKEY
menukey = getc();
# else
(void) getc(); /* consume input */
# endif
break;
}
udelay(10000);
} while (!abort && get_timer(ts) < 1000);
printf("\b\b\b%2d ", bootdelay);
}
putc('\n');
return abort;
}这里判断如果bootdelay是大于0的，也就定义了bootdelay的时间，那么打印Hit any key to stop autoboot:，提示按下任意键即可终止自动启动，然后函数检测有无按键按下，如果有按键按下，则don't auto boot，并将abort置1，bootdelay置0.
最后函数返回abort。
然后回到autoboot_command函数的判断式中，如果按键没有按下，也就是abort函数返回0，判断式条件成立，将禁用ctrl+c按键，并调用run_command_list函数，该函数执行从环境变量读取的bootcmd的值，也就是s。
该函数在cli.c文件中：
int run_command_list(const char *cmd, int len, int flag)
{
int need_buff = 1;
char *buff = (char *)cmd; /* cast away const */
int rcode = 0;
if (len == -1) {
len = strlen(cmd);
#ifdef CONFIG_HUSH_PARSER
/* hush will never change our string */
need_buff = 0;
#else
/* the built-in parser will change our string if it sees \n */
need_buff = strchr(cmd, '\n') != NULL;
#endif
}
if (need_buff) {
buff = malloc(len + 1);
if (!buff)
return 1;
memcpy(buff, cmd, len);
buff[len] = '\0';
}
#ifdef CONFIG_HUSH_PARSER
rcode = parse_string_outer(buff, FLAG_PARSE_SEMICOLON);
#else
/*
* This function will overwrite any \n it sees with a \0, which
* is why it can't work with a const char *. Here we are making
* using of internal knowledge of this function, to avoid always
* doing a malloc() which is actually required only in a case that
* is pretty rare.
*/
#ifdef CONFIG_CMDLINE
rcode = cli_simple_run_command_list(buff, flag);
#else
rcode = board_run_command(buff);
#endif
#endif
if (need_buff)
free(buff);
return rcode;
}该函数通过parse_string_outer函数调用了bush_shell的命令解释器parse_stream_outer函数来解释bootcmd的命令，而环境变量bootcmd的启动命令用来设置linux必要的启动环境，board_run_command执行命令。然后加载和启动内核。那么board_run_command如何执行命令呢？
board_run_command函数通过bootcmd参数中的bootm命令找到\cmd\bootm.c中的bootm_maybe_autostart函数中的
U_BOOT_CMD(
bootm, CONFIG_SYS_MAXARGS, 1, do_bootm,
"boot application image from memory", bootm_help_text
);然后根据这个信息找到执行bootm命令的处理函数指针do_bootm,并进入do_bootm函数执行相关代码，U_BOOT_CMD在/include/command.h中定义。
do_bootm函数（/cmd/bootm.c）
/*******************************************************************/
/* bootm - boot application image from image in memory */
/*******************************************************************/
int do_bootm(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
#ifdef CONFIG_NEEDS_MANUAL_RELOC
static int relocated = 0;
if (!relocated) {
int i;
/* relocate names of sub-command table */
for (i = 0; i < ARRAY_SIZE(cmd_bootm_sub); i++)
cmd_bootm_sub[i].name += gd->reloc_off;
relocated = 1;
}
#endif
/* determine if we have a sub command */
argc--; argv++;
if (argc > 0) {
char *endp;
simple_strtoul(argv[0], &endp, 16);
/* endp pointing to NULL means that argv[0] was just a
* valid number, pass it along to the normal bootm processing
*
* If endp is ':' or '#' assume a FIT identifier so pass
* along for normal processing.
*
* Right now we assume the first arg should never be '-'
*/
if ((*endp != 0) && (*endp != ':') && (*endp != '#'))
return do_bootm_subcommand(cmdtp, flag, argc, argv);
}
return do_bootm_states(cmdtp, flag, argc, argv, BOOTM_STATE_START |
BOOTM_STATE_FINDOS | BOOTM_STATE_FINDOTHER |
BOOTM_STATE_LOADOS |
#ifdef CONFIG_SYS_BOOT_RAMDISK_HIGH
BOOTM_STATE_RAMDISK |
#endif
#if defined(CONFIG_PPC) || defined(CONFIG_MIPS)
BOOTM_STATE_OS_CMDLINE |
#endif
BOOTM_STATE_OS_PREP | BOOTM_STATE_OS_FAKE_GO |
BOOTM_STATE_OS_GO, &images, 1);
}
从do_bootm进入/common/bootm.c：do_bootm_states函数，Now run the OS！
int do_bootm_states(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[],
int states, bootm_headers_t *images, int boot_progress)
{
boot_os_fn *boot_fn;
ulong iflag = 0;
int ret = 0, need_boot_fn;
images->state |= states;
/*
* Work through the states and see how far we get. We stop on
* any error.
*/
if (states & BOOTM_STATE_START)
ret = bootm_start(cmdtp, flag, argc, argv);
if (!ret && (states & BOOTM_STATE_FINDOS))
ret = bootm_find_os(cmdtp, flag, argc, argv);
if (!ret && (states & BOOTM_STATE_FINDOTHER))
ret = bootm_find_other(cmdtp, flag, argc, argv);
/* Load the OS */
if (!ret && (states & BOOTM_STATE_LOADOS)) {
ulong load_end;
iflag = bootm_disable_interrupts();
ret = bootm_load_os(images, &load_end, 0);
if (ret == 0)
lmb_reserve(&images->lmb, images->os.load,
(load_end - images->os.load));
else if (ret && ret != BOOTM_ERR_OVERLAP)
goto err;
else if (ret == BOOTM_ERR_OVERLAP)
ret = 0;
}
/* Relocate the ramdisk */
#ifdef CONFIG_SYS_BOOT_RAMDISK_HIGH
if (!ret && (states & BOOTM_STATE_RAMDISK)) {
ulong rd_len = images->rd_end - images->rd_start;
ret = boot_ramdisk_high(&images->lmb, images->rd_start,
rd_len, &images->initrd_start, &images->initrd_end);
if (!ret) {
env_set_hex("initrd_start", images->initrd_start);
env_set_hex("initrd_end", images->initrd_end);
}
}
#endif
#if IMAGE_ENABLE_OF_LIBFDT && defined(CONFIG_LMB)
if (!ret && (states & BOOTM_STATE_FDT)) {
boot_fdt_add_mem_rsv_regions(&images->lmb, images->ft_addr);
ret = boot_relocate_fdt(&images->lmb, &images->ft_addr,
&images->ft_len);
}
#endif
/* From now on, we need the OS boot function */
if (ret)
return ret;
boot_fn = bootm_os_get_boot_func(images->os.os);
need_boot_fn = states & (BOOTM_STATE_OS_CMDLINE |
BOOTM_STATE_OS_BD_T | BOOTM_STATE_OS_PREP |
BOOTM_STATE_OS_FAKE_GO | BOOTM_STATE_OS_GO);
if (boot_fn == NULL && need_boot_fn) {
if (iflag)
enable_interrupts();
printf("ERROR: booting os '%s' (%d) is not supported\n",
genimg_get_os_name(images->os.os), images->os.os);
bootstage_error(BOOTSTAGE_ID_CHECK_BOOT_OS);
return 1;
}
/* Call various other states that are not generally used */
if (!ret && (states & BOOTM_STATE_OS_CMDLINE))
ret = boot_fn(BOOTM_STATE_OS_CMDLINE, argc, argv, images);
if (!ret && (states & BOOTM_STATE_OS_BD_T))
ret = boot_fn(BOOTM_STATE_OS_BD_T, argc, argv, images);
if (!ret && (states & BOOTM_STATE_OS_PREP)) {
#if defined(CONFIG_SILENT_CONSOLE) && !defined(CONFIG_SILENT_U_BOOT_ONLY)
if (images->os.os == IH_OS_LINUX)
fixup_silent_linux();
#endif
ret = boot_fn(BOOTM_STATE_OS_PREP, argc, argv, images);
}
#ifdef CONFIG_TRACE
/* Pretend to run the OS, then run a user command */
if (!ret && (states & BOOTM_STATE_OS_FAKE_GO)) {
char *cmd_list = env_get("fakegocmd");
ret = boot_selected_os(argc, argv, BOOTM_STATE_OS_FAKE_GO,
images, boot_fn);
if (!ret && cmd_list)
ret = run_command_list(cmd_list, -1, flag);
}
#endif
/* Check for unsupported subcommand. */
if (ret) {
puts("subcommand not supported\n");
return ret;
}
/* Now run the OS! We hope this doesn't return */
if (!ret && (states & BOOTM_STATE_OS_GO))
ret = boot_selected_os(argc, argv, BOOTM_STATE_OS_GO,
images, boot_fn);
/* Deal with any fallout */
err:
if (iflag)
enable_interrupts();
if (ret == BOOTM_ERR_UNIMPLEMENTED)
bootstage_error(BOOTSTAGE_ID_DECOMP_UNIMPL);
else if (ret == BOOTM_ERR_RESET)
do_reset(cmdtp, flag, argc, argv);
return ret;
}
其中主要函数 bootm_find_os 实现三个功能：get kernel image header， start address and length，get image parameters。大概过程是：bootm_find_os -> boot_get_kernel -> image_get_kernel
static int bootm_find_os(cmd_tbl_t *cmdtp, int flag, int argc,
char * const argv[])
{
const void *os_hdr;
bool ep_found = false;
int ret;
/* get kernel image header, start address and length */
os_hdr = boot_get_kernel(cmdtp, flag, argc, argv,
&images, &images.os.image_start, &images.os.image_len);
if (images.os.image_len == 0) {
puts("ERROR: can't get kernel image!\n");
return 1;
}
/* get image parameters */
switch (genimg_get_format(os_hdr)) {
#if defined(CONFIG_IMAGE_FORMAT_LEGACY)
case IMAGE_FORMAT_LEGACY:
images.os.type = image_get_type(os_hdr);
images.os.comp = image_get_comp(os_hdr);
images.os.os = image_get_os(os_hdr);
images.os.end = image_get_image_end(os_hdr);
images.os.load = image_get_load(os_hdr);
images.os.arch = image_get_arch(os_hdr);
break;
#endif
#if IMAGE_ENABLE_FIT
case IMAGE_FORMAT_FIT:
if (fit_image_get_type(images.fit_hdr_os,
images.fit_noffset_os,
&images.os.type)) {
puts("Can't get image type!\n");
bootstage_error(BOOTSTAGE_ID_FIT_TYPE);
return 1;
}
if (fit_image_get_comp(images.fit_hdr_os,
images.fit_noffset_os,
&images.os.comp)) {
puts("Can't get image compression!\n");
bootstage_error(BOOTSTAGE_ID_FIT_COMPRESSION);
return 1;
}
if (fit_image_get_os(images.fit_hdr_os, images.fit_noffset_os,
&images.os.os)) {
puts("Can't get image OS!\n");
bootstage_error(BOOTSTAGE_ID_FIT_OS);
return 1;
}
if (fit_image_get_arch(images.fit_hdr_os,
images.fit_noffset_os,
&images.os.arch)) {
puts("Can't get image ARCH!\n");
return 1;
}
images.os.end = fit_get_end(images.fit_hdr_os);
if (fit_image_get_load(images.fit_hdr_os, images.fit_noffset_os,
&images.os.load)) {
puts("Can't get image load address!\n");
bootstage_error(BOOTSTAGE_ID_FIT_LOADADDR);
return 1;
}
break;
#endif
#ifdef CONFIG_ANDROID_BOOT_IMAGE
case IMAGE_FORMAT_ANDROID:
images.os.type = IH_TYPE_KERNEL;
images.os.comp = IH_COMP_NONE;
images.os.os = IH_OS_LINUX;
images.os.end = android_image_get_end(os_hdr);
images.os.load = android_image_get_kload(os_hdr);
images.ep = images.os.load;
ep_found = true;
break;
#endif
default:
puts("ERROR: unknown image format type!\n");
return 1;
}
/* If we have a valid setup.bin, we will use that for entry (x86) */
if (images.os.arch == IH_ARCH_I386 ||
images.os.arch == IH_ARCH_X86_64) {
ulong len;
ret = boot_get_setup(&images, IH_ARCH_I386, &images.ep, &len);
if (ret < 0 && ret != -ENOENT) {
puts("Could not find a valid setup.bin for x86\n");
return 1;
}
/* Kernel entry point is the setup.bin */
} else if (images.legacy_hdr_valid) {
images.ep = image_get_ep(&images.legacy_hdr_os_copy);
#if IMAGE_ENABLE_FIT
} else if (images.fit_uname_os) {
int ret;
ret = fit_image_get_entry(images.fit_hdr_os,
images.fit_noffset_os, &images.ep);
if (ret) {
puts("Can't get entry point property!\n");
return 1;
}
#endif
} else if (!ep_found) {
puts("Could not find kernel entry point!\n");
return 1;
}
if (images.os.type == IH_TYPE_KERNEL_NOLOAD) {
images.os.load = images.os.image_start;
images.ep += images.os.load;
}
images.os.start = map_to_sysmem(os_hdr);
return 0;
}回到do_bootm_states往下看可以知道由boot_fn = bootm_os_get_boot_func（images->os.os）;（images->os.os是系统内核的类型，若系统位Linux，则为5。操作系统代号在/include/image.h查看）得到boot处理函数指针并赋给boot_fn。
bootm_os_get_boot_func中会用到函数指针数组boot_os，该数组利用传入的images.os.os=5的值得到boot处理函数指针do_bootm_linux返回给boot_fn 。
从do_bootm_states进入\common\bootm_os.c：boot_selected_os函数，执行boot_fn（state， argc， argv， images）;
执行boot_fn（state， argc， argv， images），因为boot_fn=do_bootm_linux，所以相当于执行do_bootm_linux（state， argc， argv， images），程序跳到\arch\arm\lib\bootm.c：
int do_bootm_linux(int flag, int argc, char * const argv[],
bootm_headers_t *images)
{
/* No need for those on ARM */
if (flag & BOOTM_STATE_OS_BD_T || flag & BOOTM_STATE_OS_CMDLINE)
return -1;
if (flag & BOOTM_STATE_OS_PREP) {
boot_prep_linux(images);
return 0;
}
if (flag & (BOOTM_STATE_OS_GO | BOOTM_STATE_OS_FAKE_GO)) {
boot_jump_linux(images, flag);
return 0;
}
boot_prep_linux(images);
boot_jump_linux(images, flag);
return 0;
}
再回到autoboot_command函数，如果有按键进行干预，那么判读式不成立，跳出执行menucmd命令：
#ifdef CONFIG_MENUKEY
if (menukey == CONFIG_MENUKEY) {
s = env_get("menucmd");
if (s)
run_command_list(s, -1, 0);
}s = getenv("menucmd");是用来获取在uboot命令行下输入的命令，menucmd就是存储命令的环境变量。然后同样运行run_command_list进行命令解释，然后跳回到main_loop函数，执行最后的cli_loop函数，也就是进入了uboot命令行模式。