本文uboot代码版本： 2016.05
跑完spl之后，如果选择了引导uboot启动，最后会进入board_init_r函数，该函数中的数组init_sequence_r中的最后一个元素run_main_loop函数包含我们要介绍的main_loop函数。
位于common/board_r.c下的board_init_r函数， 会按顺序调用数组init_seqence_r里面的函数
void board_init_r(gd_t *new_gd, ulong dest_addr)
{
#ifdef CONFIG_NEEDS_MANUAL_RELOC
int i;
#endif
#ifdef CONFIG_AVR32
mmu_init_r(dest_addr);
#endif
#if !defined(CONFIG_X86) && !defined(CONFIG_ARM) && !defined(CONFIG_ARM64)
gd = new_gd;
#endif
#ifdef CONFIG_NEEDS_MANUAL_RELOC
for (i = 0; i < ARRAY_SIZE(init_sequence_r); i++)
init_sequence_r[i] += gd->reloc_off;
#endif
if (initcall_run_list(init_sequence_r))
hang();
/* NOTREACHED - run_main_loop() does not return */
hang();
}
位于common/board_r.c 的数组 init_sequence_r，数组最后为run_main_loop函数
init_fnc_t init_sequence_r[] = {
initr_trace,
initr_reloc,
/* TODO: could x86/PPC have this also perhaps? */
#ifdef CONFIG_ARM
initr_caches,
/* Note: For Freescale LS2 SoCs, new MMU table is created in DDR.
* A temporary mapping of IFC high region is since removed,
* so environmental variables in NOR flash is not availble
* until board_init() is called below to remap IFC to high
* region.
*/
#endif
initr_reloc_global_data,
#if defined(CONFIG_SYS_INIT_RAM_LOCK) && defined(CONFIG_E500)
initr_unlock_ram_in_cache,
#endif
initr_barrier,
initr_malloc,
initr_console_record,
#ifdef CONFIG_SYS_NONCACHED_MEMORY
initr_noncached,
#endif
bootstage_relocate,
#ifdef CONFIG_DM
initr_dm,
#endif
initr_bootstage,
#if defined(CONFIG_ARM) || defined(CONFIG_NDS32)
board_init, /* Setup chipselects */
#endif
/*
* TODO: printing of the clock inforamtion of the board is now
* implemented as part of bdinfo command. Currently only support for
* davinci SOC's is added. Remove this check once all the board
* implement this.
*/
#ifdef CONFIG_CLOCKS
set_cpu_clk_info, /* Setup clock information */
#endif
#ifdef CONFIG_EFI_LOADER
efi_memory_init,
#endif
stdio_init_tables,
initr_serial,
initr_announce,
INIT_FUNC_WATCHDOG_RESET
#ifdef CONFIG_NEEDS_MANUAL_RELOC
initr_manual_reloc_cmdtable,
#endif
#if defined(CONFIG_PPC) || defined(CONFIG_M68K)
initr_trap,
#endif
#ifdef CONFIG_ADDR_MAP
initr_addr_map,
#endif
#if defined(CONFIG_BOARD_EARLY_INIT_R)
board_early_init_r,
#endif
INIT_FUNC_WATCHDOG_RESET
#ifdef CONFIG_LOGBUFFER
initr_logbuffer,
#endif
#ifdef CONFIG_POST
initr_post_backlog,
#endif
INIT_FUNC_WATCHDOG_RESET
#ifdef CONFIG_SYS_DELAYED_ICACHE
initr_icache_enable,
#endif
#if defined(CONFIG_PCI) && defined(CONFIG_SYS_EARLY_PCI_INIT)
/*
* Do early PCI configuration _before_ the flash gets initialised,
* because PCU ressources are crucial for flash access on some boards.
*/
initr_pci,
#endif
#ifdef CONFIG_WINBOND_83C553
initr_w83c553f,
#endif
#ifdef CONFIG_ARCH_EARLY_INIT_R
arch_early_init_r,
#endif
power_init_board,
#ifndef CONFIG_SYS_NO_FLASH
initr_flash,
#endif
INIT_FUNC_WATCHDOG_RESET
#if defined(CONFIG_PPC) || defined(CONFIG_M68K) || defined(CONFIG_X86) ||
defined(CONFIG_SPARC)
/* initialize higher level parts of CPU like time base and timers */
cpu_init_r,
#endif
#ifdef CONFIG_PPC
initr_spi,
#endif
#ifdef CONFIG_CMD_NAND
initr_nand,
#endif
#ifdef CONFIG_CMD_ONENAND
initr_onenand,
#endif
#ifdef CONFIG_GENERIC_MMC
initr_mmc,
#endif
#ifdef CONFIG_HAS_DATAFLASH
initr_dataflash,
#endif
initr_env,
#ifdef CONFIG_SYS_BOOTPARAMS_LEN
initr_malloc_bootparams,
#endif
INIT_FUNC_WATCHDOG_RESET
initr_secondary_cpu,
#if defined(CONFIG_ID_EEPROM) || defined(CONFIG_SYS_I2C_MAC_OFFSET)
mac_read_from_eeprom,
#endif
INIT_FUNC_WATCHDOG_RESET
#if defined(CONFIG_PCI) && !defined(CONFIG_SYS_EARLY_PCI_INIT)
/*
* Do pci configuration
*/
initr_pci,
#endif
stdio_add_devices,
initr_jumptable,
#ifdef CONFIG_API
initr_api,
#endif
console_init_r, /* fully init console as a device */
#ifdef CONFIG_DISPLAY_BOARDINFO_LATE
show_board_info,
#endif
#ifdef CONFIG_ARCH_MISC_INIT
arch_misc_init, /* miscellaneous arch-dependent init */
#endif
#ifdef CONFIG_MISC_INIT_R
misc_init_r, /* miscellaneous platform-dependent init */
#endif
INIT_FUNC_WATCHDOG_RESET
#ifdef CONFIG_CMD_KGDB
initr_kgdb,
#endif
interrupt_init,
#if defined(CONFIG_ARM) || defined(CONFIG_AVR32)
initr_enable_interrupts,
#endif
#if defined(CONFIG_MICROBLAZE) || defined(CONFIG_AVR32) || defined(CONFIG_M68K)
timer_init, /* initialize timer */
#endif
#if defined(CONFIG_STATUS_LED)
initr_status_led,
#endif
/* PPC has a udelay(20) here dating from 2002. Why? */
#ifdef CONFIG_CMD_NET
initr_ethaddr,
#endif
#ifdef CONFIG_BOARD_LATE_INIT
board_late_init,
#endif
#if defined(CONFIG_CMD_AMBAPP)
ambapp_init_reloc,
#if defined(CONFIG_SYS_AMBAPP_PRINT_ON_STARTUP)
initr_ambapp_print,
#endif
#endif
#ifdef CONFIG_CMD_SCSI
INIT_FUNC_WATCHDOG_RESET
initr_scsi,
#endif
#ifdef CONFIG_CMD_DOC
INIT_FUNC_WATCHDOG_RESET
initr_doc,
#endif
#ifdef CONFIG_BITBANGMII
initr_bbmii,
#endif
#ifdef CONFIG_CMD_NET
INIT_FUNC_WATCHDOG_RESET
initr_net,
#endif
#ifdef CONFIG_POST
initr_post,
#endif
#if defined(CONFIG_CMD_PCMCIA) && !defined(CONFIG_CMD_IDE)
initr_pcmcia,
#endif
#if defined(CONFIG_CMD_IDE)
initr_ide,
#endif
#ifdef CONFIG_LAST_STAGE_INIT
INIT_FUNC_WATCHDOG_RESET
/*
* Some parts can be only initialized if all others (like
* Interrupts) are up and running (i.e. the PC-style ISA
* keyboard).
*/
last_stage_init,
#endif
#ifdef CONFIG_CMD_BEDBUG
INIT_FUNC_WATCHDOG_RESET
initr_bedbug,
#endif
#if defined(CONFIG_PRAM) || defined(CONFIG_LOGBUFFER)
initr_mem,
#endif
#ifdef CONFIG_PS2KBD
initr_kbd,
#endif
#if defined(CONFIG_SPARC)
prom_init,
#endif
run_main_loop,
};
位于同一目录下的run_main_loop函数，可以看到在一个死循环里面执行main_loop函数，也就是说run_main_loop永远不会返回。
static int run_main_loop(void)
{
#ifdef CONFIG_SANDBOX
sandbox_main_loop_init();
#endif
/* main_loop() can return to retry autoboot, if so just run it again */
for (;;)
main_loop();
return 0;
}
以下为位于common/main.c下面的main_loop函数，bootstage_mark_name函数最终调用了show_boot_progress函数，该函数为空函数
/* We come here after U-Boot is initialised and ready to process commands */
void main_loop(void)
{
const char *s;
bootstage_mark_name(BOOTSTAGE_ID_MAIN_LOOP, "main_loop");
#ifndef CONFIG_SYS_GENERIC_BOARD
puts("Warning: Your board does not use generic board. Please read
");
puts("doc/README.generic-board and take action. Boards not
");
puts("upgraded by the late 2014 may break or be removed.
");
#endif
#ifdef CONFIG_VERSION_VARIABLE
setenv("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");
}
setenv函数如下所示，用于设置环境变量ver为version_string
version_string在common/cmd_version.c定义为
const char __weak version_string[] = U_BOOT_VERSION_STRING;
U_BOOT_VERSION_STRING在include/version.h中定义为
#define U_BOOT_VERSION_STRING U_BOOT_VERSION " (" U_BOOT_DATE " - "
U_BOOT_TIME " " U_BOOT_TZ ")" CONFIG_IDENT_STRING
U_BOOT_VERSION, U_BOOT_DATE, U_BOOT_TIME, U_BOOT_TZ这几个宏在include/generated/version_autogenerated.h和include/generated/timestamp_autogenerated.h中被定义,CONFIG_IDENT_STRING在include/version.h中被定义为空("")
//nclude/generated/version_autogenerated.h 这个头文件在编译的时候自动生成
define PLAIN_VERSION "2016.05-00297-ge4b7ffa-dirty"
#define U_BOOT_VERSION "U-Boot " PLAIN_VERSION
#define CC_VERSION_STRING "arm-linux-gnueabihf-gcc (Linaro GCC 5.3-2016.02) 5.3.1 20160113"
#define LD_VERSION_STRING "GNU ld (GNU Binutils) 2.25.0 Linaro 2015_10"
//include/generated/timestamp_autogenerated.h 这个头文件在编译的时候自动生成
#define U_BOOT_DATE "Sep 11 2019"
#define U_BOOT_TIME "21:00:25"
#define U_BOOT_TZ "+0800"
#define U_BOOT_DMI_DATE "09/11/2019"
uboot起来之后可以通过printenv命令查看当前所设置的环境变量，其中就有ver这个环境变量
varname = "ver"
varvalue = "U-Boot 2016.05-00297-ge4b7ffa-dirty (Sep 11 2019 - 19:24:32 +0800)"
int setenv(const char *varname, const char *varvalue)
{
const char * const argv[4] = { "setenv", varname, varvalue, NULL };
/* before import into hashtable */
if (!(gd->flags & GD_FLG_ENV_READY))
return 1;
if (varvalue == NULL || varvalue[0] == ' ')
return _do_env_set(0, 2, (char * const *)argv, H_PROGRAMMATIC);
else
return _do_env_set(0, 3, (char * const *)argv, H_PROGRAMMATIC);
}
varname和varvalue都不为空，所以接着执行 _do_env_set(0, 3, (char * const *)argv, H_PROGRAMMATIC);
/*
* Set a new environment variable,
* or replace or delete an existing one.
*/
static int _do_env_set(int flag, int argc, char * const argv[], int env_flag)
{
int i, len;
char *name, *value, *s;
ENTRY e, *ep;
debug("Initial value for argc=%d
", argc);
while (argc > 1 && **(argv + 1) == '-') { //argv[1] = "ver", 跳过此循环
char *arg = *++argv;
--argc;
while (*++arg) {
switch (*arg) {
case 'f': /* force */
env_flag |= H_FORCE;
break;
default:
return CMD_RET_USAGE;
}
}
}
debug("Final value for argc=%d
", argc);
name = argv[1];//"ver"
value = argv[2];//"U-Boot 2016.05-00297-ge4b7ffa-dirty (Sep 11 2019 - 20:31:15 +0800)"
if (strchr(name, '=')) {//判断name中是否有 “=”这个字符，如没有返回NULL，此处条件不成立
printf("## Error: illegal character '='"
"in variable name "%s"
", name);
return 1;
}
env_id++;
/* Delete only ? */
if (argc < 3 || argv[2] == NULL) {//如果第3个参数为NULL，就删除这变量
int rc = hdelete_r(name, &env_htab, env_flag);
return !rc;
}
/*
* Insert / replace new value
*/
for (i = 2, len = 0; i < argc; ++i)
len += strlen(argv[i]) + 1;
value = malloc(len);
if (value == NULL) {
printf("## Can't malloc %d bytes
", len);
return 1;
}
for (i = 2, s = value; i < argc; ++i) {
char *v = argv[i];
while ((*s++ = *v++) != ' ')
;
printf("s: [%s]
", s);
*(s - 1) = ' ';
}
if (s != value)
*--s = ' ';
e.key = name;
e.data = value;
hsearch_r(e, ENTER, &ep, &env_htab, env_flag);
free(value);
if (!ep) {
printf("## Error inserting "%s" variable, errno=%d
",
name, errno);
return 1;
}
return 0;
}
接下来执行cli_init函数，在common/cli.c中对函数的定义如下，如果定义了CONFIG_SYS_HUSH_PARSER则支持hush shell，一个据说来自busybox的命令解析器
void cli_init(void)
{
#ifdef CONFIG_SYS_HUSH_PARSER
u_boot_hush_start();
#endif
#if defined(CONFIG_HUSH_INIT_VAR)
hush_init_var();
#endif
}
run_preboot_environment_command函数从环境变量中获取preboot的定义，该变量包含了一些预启动命令，一般环境变量中不包含该项配置。我目前所用的系统也没有定义该配置，因为没有定义CONFIG_UPDATE_TFTP，所以先不管update_tftp这个函数
static void run_preboot_environment_command(void)
{
#ifdef CONFIG_PREBOOT
char *p;
p = getenv("preboot");
if (p != NULL) {
# ifdef CONFIG_AUTOBOOT_KEYED
int prev = disable_ctrlc(1); /* disable Control C checking */
# endif
run_command_list(p, -1, 0);
# ifdef CONFIG_AUTOBOOT_KEYED
disable_ctrlc(prev); /* restore Control C checking */
# endif
}
#endif /* CONFIG_PREBOOT */
}
函数bootdelay_process在common/autoboot.c中定义，用于获取环境变量bootdelay的值并转成整数后保存在全局变量stored_bootdelay中，最后获取bootcmd的配置值作为函数的返回值。
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);
setenv_ulong("bootcount", bootcount);
bootlimit = getenv_ulong("bootlimit", 10, 0);
#endif /* CONFIG_BOOTCOUNT_LIMIT */
s = getenv("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
", 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 = getenv("failbootcmd");
} else
#endif /* CONFIG_POST */
#ifdef CONFIG_BOOTCOUNT_LIMIT
if (bootlimit && (bootcount > bootlimit)) {
printf("Warning: Bootlimit (%u) exceeded. Using altbootcmd.
",
(unsigned)bootlimit);
s = getenv("altbootcmd");
} else
#endif /* CONFIG_BOOTCOUNT_LIMIT */
s = getenv("bootcmd");
process_fdt_options(gd->fdt_blob);
stored_bootdelay = bootdelay;
return s;
}
函数cli_process_fdt，在这里一直是false，所以不会回执行cli_secure_boot_cmd函数
往下执行定义在common/autoboot.c的autoboot_command函数
void autoboot_command(const char *s)
{
debug("### main_loop: bootcmd="%s"
", 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 = getenv("menucmd");
if (s)
run_command_list(s, -1, 0);
}
#endif /* CONFIG_MENUKEY */
}
上面第一个if中的函数abortboot函数如下，由于没有定义CONFIG_AUTOBOOT_KEYED，所以会调用abortboot_normal函数，在bootdelay时间内如果没有用户干预，没有按任何键盘键，则这个函数
顺利执行完，往下执行run_command_list函数，执行环境变量bootcmd里面的一大堆命令，尝试启动并计入linux内核；
假若在bootdelay时间按下了任何键，abortboot函数返回1。
tatic int abortboot(int bootdelay)
{
#ifdef CONFIG_AUTOBOOT_KEYED
return abortboot_keyed(bootdelay);
#else
return abortboot_normal(bootdelay);
#endif
}
则继续往下执行cli_loop运行hush shell解释器：
void cli_loop(void)
{
#ifdef CONFIG_SYS_HUSH_PARSER
parse_file_outer();
/* This point is never reached */
for (;;);
#elif defined(CONFIG_CMDLINE)
cli_simple_loop();
#else
printf("## U-Boot command line is disabled. Please enable CONFIG_CMDLINE
");
#endif /*CONFIG_SYS_HUSH_PARSER*/
}
parse_file_outer进行必要的初始化之后，将调用parse_strea_outer函数；
/* most recursion does not come through here, the exeception is
* from builtin_source() */
static int parse_stream_outer(struct in_str *inp, int flag)
{
struct p_context ctx;
o_string temp=NULL_O_STRING;
int rcode;
#ifdef __U_BOOT__
int code = 1;
#endif
do {
ctx.type = flag;
initialize_context(&ctx);
update_ifs_map();
if (!(flag & FLAG_PARSE_SEMICOLON) || (flag & FLAG_REPARSING)) mapset((uchar *)";$&|", 0);
inp->promptmode=1;
rcode = parse_stream(&temp, &ctx, inp,
flag & FLAG_CONT_ON_NEWLINE ? -1 : '
');
#ifdef __U_BOOT__
if (rcode == 1) flag_repeat = 0;
#endif
if (rcode != 1 && ctx.old_flag != 0) {
syntax();
#ifdef __U_BOOT__
flag_repeat = 0;
#endif
}
if (rcode != 1 && ctx.old_flag == 0) {
done_word(&temp, &ctx);
done_pipe(&ctx,PIPE_SEQ);
#ifndef __U_BOOT__
run_list(ctx.list_head);
#else
code = run_list(ctx.list_head);
if (code == -2) { /* exit */
b_free(&temp);
code = 0;
/* XXX hackish way to not allow exit from main loop */
if (inp->peek == file_peek) {
printf("exit not allowed from main input shell.
");
continue;
}
break;
}
if (code == -1)
flag_repeat = 0;
#endif
} else {
if (ctx.old_flag != 0) {
free(ctx.stack);
b_reset(&temp);
}
#ifdef __U_BOOT__
if (inp->__promptme == 0) printf("<INTERRUPT>
");
inp->__promptme = 1;
#endif
temp.nonnull = 0;
temp.quote = 0;
inp->p = NULL;
free_pipe_list(ctx.list_head,0);
}
b_free(&temp);
/* loop on syntax errors, return on EOF */
} while (rcode != -1 && !(flag & FLAG_EXIT_FROM_LOOP) &&
(inp->peek != static_peek || b_peek(inp)));
#ifndef __U_BOOT__
return 0;
#else
return (code != 0) ? 1 : 0;
#endif /* __U_BOOT__ */
}
上面的do-while循环执行并解释uboot的命令，也就是我们看到的命令行模式