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uboot代码解析1：根据目的找主线
2022-08-11 05:32:00 【千册】
https://ke.qq.com/course/4032547?flowToken=1042705
为什么要解析uboot代码呢？当然是因为遇到棘手的问题啦。
目录
void board_init_r(gd_t *new_gd, ulong dest_addr)
void board_init_f(ulong dummy)
结构体typedef struct bootm_headers
前言
先记住这几个东西
全局变量:gd
全局数组：init_sequence_r
函数：main_loop,
linux启动入口函数do_bootm_linux
结构体typedef struct bootm_headers ：要研究ramdisk，就得研究它，
它是我此次分析的重点和主线，这就是我的目的，解决ramdisk问题。
把复杂的事情简单化，就是功力。
一 uboot启动都干了什么
uboot启动以后，先初始化各种硬件，然后进入main_loop,等待用户的交互操作，bootdelay是uboot里的一个环境变量，里面存放着整数，存储秒数，将bootdelay秒时间，uboot未接收到交互信号，就进入linux内核，并结束自己的生命。
uboot根据bootcmd加载zImage和设备树，然后将设备树和bootargs传递给内核。然后内核根据设备树初始化外设，不同的设备树，决定了zImage使用在不同的设备上，例如同一款产品的不同系列，高配版和低配版。
二 找方法
分析代码，讲究方式方法。
第一确定找主线。
其次就是有目的。目的就是动力，不忘初心牢记使命，方得始终。
例如你想修改网卡的MAC地址，或者想修添加一个自定义的命令，也可以向在uboot设置仅通过网络网络启动内核，无论是什么，找到一个目的
三 我的目的:解决ramdisk问题
uboot的是一个大号的裸板程序，裸板程序的特点就是有一个死循环，那就是main_loop，
第一个函数
main_loop
这个函数主要就是和用户交互的，就是解析用户输入的命令，然后给出结果。
main_loop被run_main_loop调用
/* 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\n");
puts("doc/README.generic-board and take action. Boards not\n");
puts("upgraded by the late 2014 may break or be removed.\n");
#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();
}
run_main_loop
这个函数很简单，就是调用的main_loop,sandbox_main_loop_init先不管。
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;
}数组init_sequence_r
run_main_loop又被赋值给了数组init_sequence_r，先看下init_sequence_r的类型和定义，init_sequence_r 是一个函数指针数组，里面被赋值各种硬件的初始化函数，看看这个数组的真身，这个数组就是初始化函数列表，里面的函数被依次调用，最后调用run_main_loop。
typedef int (*init_fnc_t)(void);
init_fnc_t init_sequence_r[]/*
* Over time we hope to remove these functions with code fragments and
* stub funtcions, and instead call the relevant function directly.
*
* We also hope to remove most of the driver-related init and do it if/when
* the driver is later used.
*
* TODO: perhaps reset the watchdog in the initcall function after each call?
*/
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
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
#ifdef CONFIG_FSL_FASTBOOT
initr_fastboot_setup,
#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
#ifdef CONFIG_FSL_FASTBOOT
initr_check_fastboot,
#endif
run_main_loop,
}void board_init_r(gd_t *new_gd, ulong dest_addr)
init_sequence_r在函数board_init_r中被调用
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();
}
void board_init_f(ulong dummy)
board_init_r被board_init_f调用
void board_init_f(ulong dummy)
{
/* setup AIPS and disable watchdog */
arch_cpu_init();
ccgr_init();
/* iomux and setup of i2c */
board_early_init_f();
/* setup GP timer */
timer_init();
/* UART clocks enabled and gd valid - init serial console */
preloader_console_init();
/* DDR initialization */
spl_dram_init();
/* Clear the BSS. */
memset(__bss_start, 0, __bss_end - __bss_start);
/* load/boot image from boot device */
board_init_r(NULL, 0);
}crt0.S
board_init_f在crt0.S被ENTRY(_main)调用，好了到头了。
ENTRY(_main)
/*
* Set up initial C runtime environment and call board_init_f(0).
*/
#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
ldr sp, =(CONFIG_SPL_STACK)
#else
ldr sp, =(CONFIG_SYS_INIT_SP_ADDR)
#endif
#if defined(CONFIG_CPU_V7M) /* v7M forbids using SP as BIC destination */
mov r3, sp
bic r3, r3, #7
mov sp, r3
#else
bic sp, sp, #7 /* 8-byte alignment for ABI compliance */
#endif
mov r0, sp
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全局变量gd_t *gd;
这些函数里还使用了一个全局变量gd，gd的类型如下所示
gd_t *gd;
研究uboot整体脉络，就是IXUS研究gd这个变量。
typedef struct global_data {
bd_t *bd;
unsigned long flags;
unsigned int baudrate;
unsigned long cpu_clk; /* CPU clock in Hz! */
unsigned long bus_clk;
/* We cannot bracket this with CONFIG_PCI due to mpc5xxx */
unsigned long pci_clk;
unsigned long mem_clk;
#if defined(CONFIG_LCD) || defined(CONFIG_VIDEO)
unsigned long fb_base; /* Base address of framebuffer mem */
#endif
#if defined(CONFIG_POST) || defined(CONFIG_LOGBUFFER)
unsigned long post_log_word; /* Record POST activities */
unsigned long post_log_res; /* success of POST test */
unsigned long post_init_f_time; /* When post_init_f started */
#endif
#ifdef CONFIG_BOARD_TYPES
unsigned long board_type;
#endif
unsigned long have_console; /* serial_init() was called */
#ifdef CONFIG_PRE_CONSOLE_BUFFER
unsigned long precon_buf_idx; /* Pre-Console buffer index */
#endif
unsigned long env_addr; /* Address of Environment struct */
unsigned long env_valid; /* Checksum of Environment valid? */
unsigned long ram_top; /* Top address of RAM used by U-Boot */
unsigned long relocaddr; /* Start address of U-Boot in RAM */
phys_size_t ram_size; /* RAM size */
#ifdef CONFIG_SYS_MEM_RESERVE_SECURE
#define MEM_RESERVE_SECURE_SECURED 0x1
#define MEM_RESERVE_SECURE_MAINTAINED 0x2
#define MEM_RESERVE_SECURE_ADDR_MASK (~0x3)
/*
* Secure memory addr
* This variable needs maintenance if the RAM base is not zero,
* or if RAM splits into non-consecutive banks. It also has a
* flag indicating the secure memory is marked as secure by MMU.
* Flags used: 0x1 secured
* 0x2 maintained
*/
phys_addr_t secure_ram;
#endif
unsigned long mon_len; /* monitor len */
unsigned long irq_sp; /* irq stack pointer */
unsigned long start_addr_sp; /* start_addr_stackpointer */
unsigned long reloc_off;
struct global_data *new_gd; /* relocated global data */
#ifdef CONFIG_DM
struct udevice *dm_root; /* Root instance for Driver Model */
struct udevice *dm_root_f; /* Pre-relocation root instance */
struct list_head uclass_root; /* Head of core tree */
#endif
#ifdef CONFIG_TIMER
struct udevice *timer; /* Timer instance for Driver Model */
#endif
const void *fdt_blob; /* Our device tree, NULL if none */
void *new_fdt; /* Relocated FDT */
unsigned long fdt_size; /* Space reserved for relocated FDT */
struct jt_funcs *jt; /* jump table */
char env_buf[32]; /* buffer for getenv() before reloc. */
#ifdef CONFIG_TRACE
void *trace_buff; /* The trace buffer */
#endif
#if defined(CONFIG_SYS_I2C)
int cur_i2c_bus; /* current used i2c bus */
#endif
#ifdef CONFIG_SYS_I2C_MXC
void *srdata[10];
#endif
unsigned long timebase_h;
unsigned long timebase_l;
#ifdef CONFIG_SYS_MALLOC_F_LEN
unsigned long malloc_base; /* base address of early malloc() */
unsigned long malloc_limit; /* limit address */
unsigned long malloc_ptr; /* current address */
#endif
#ifdef CONFIG_PCI
struct pci_controller *hose; /* PCI hose for early use */
phys_addr_t pci_ram_top; /* top of region accessible to PCI */
#endif
#ifdef CONFIG_PCI_BOOTDELAY
int pcidelay_done;
#endif
struct udevice *cur_serial_dev; /* current serial device */
struct arch_global_data arch; /* architecture-specific data */
#ifdef CONFIG_CONSOLE_RECORD
struct membuff console_out; /* console output */
struct membuff console_in; /* console input */
#endif
#ifdef CONFIG_DM_VIDEO
ulong video_top; /* Top of video frame buffer area */
ulong video_bottom; /* Bottom of video frame buffer area */
#endif
}do_bootm_linux :linux内核的入口函数
一切事物终将走向灭亡，但也会迎来心生，uboot死亡的时候，就是内核出生的地方。
/* Main Entry point for arm bootm implementation
*
* Modeled after the powerpc implementation
* DIFFERENCE: Instead of calling prep and go at the end
* they are called if subcommand is equal 0.
*/
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;
}结构体typedef struct bootm_headers
typedef struct bootm_headers {
/*
* Legacy os image header, if it is a multi component image
* then boot_get_ramdisk() and get_fdt() will attempt to get
* data from second and third component accordingly.
*/
image_header_t *legacy_hdr_os; /* image header pointer */
image_header_t legacy_hdr_os_copy; /* header copy */
ulong legacy_hdr_valid;
#if defined(CONFIG_FIT)
const char *fit_uname_cfg; /* configuration node unit name */
void *fit_hdr_os; /* os FIT image header */
const char *fit_uname_os; /* os subimage node unit name */
int fit_noffset_os; /* os subimage node offset */
void *fit_hdr_rd; /* init ramdisk FIT image header */
const char *fit_uname_rd; /* init ramdisk subimage node unit name */
int fit_noffset_rd; /* init ramdisk subimage node offset */
void *fit_hdr_fdt; /* FDT blob FIT image header */
const char *fit_uname_fdt; /* FDT blob subimage node unit name */
int fit_noffset_fdt;/* FDT blob subimage node offset */
void *fit_hdr_setup; /* x86 setup FIT image header */
const char *fit_uname_setup; /* x86 setup subimage node name */
int fit_noffset_setup;/* x86 setup subimage node offset */
#endif
#ifndef USE_HOSTCC
image_info_t os; /* os image info */
ulong ep; /* entry point of OS */
ulong rd_start, rd_end;/* ramdisk start/end */
char *ft_addr; /* flat dev tree address */
ulong ft_len; /* length of flat device tree */
ulong initrd_start;
ulong initrd_end;
ulong cmdline_start;
ulong cmdline_end;
bd_t *kbd;
#endif
int verify; /* getenv("verify")[0] != 'n' */
#define BOOTM_STATE_START (0x00000001)
#define BOOTM_STATE_FINDOS (0x00000002)
#define BOOTM_STATE_FINDOTHER (0x00000004)
#define BOOTM_STATE_LOADOS (0x00000008)
#define BOOTM_STATE_RAMDISK (0x00000010)
#define BOOTM_STATE_FDT (0x00000020)
#define BOOTM_STATE_OS_CMDLINE (0x00000040)
#define BOOTM_STATE_OS_BD_T (0x00000080)
#define BOOTM_STATE_OS_PREP (0x00000100)
#define BOOTM_STATE_OS_FAKE_GO (0x00000200) /* 'Almost' run the OS */
#define BOOTM_STATE_OS_GO (0x00000400)
int state;
#ifdef CONFIG_LMB
struct lmb lmb; /* for memory mgmt */
#endif
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