当前位置：网站首页>uboot code analysis 1: find the main line according to the purpose

uboot启动以后,Initialize various hardware first,然后进入main_loop,Waiting for user interaction,bootdelay是uboot里的一个环境变量,里面存放着整数,Stores the seconds,将bootdelay秒时间,ubootNo interaction signal received,就进入linux内核,and end his own life.

uboot根据bootcmd加载zImage和设备树,Then move the device tree and bootargs传递给内核.The kernel then initializes the peripherals according to the device tree,Different device trees,决定了zImageused on different devices,For example, different series of the same product,High and low version.

二找方法

分析代码,讲究方式方法.

First make sure to find the main thread.

The second is purpose.Purpose is motivation,不忘初心牢记使命,方得始终.

For example, you want to modify the network cardMAC地址,Or want to fix adding a custom command,Also available toubootSet to only start the kernel over the network network,无论是什么,Find a purpose

三我的目的:解决ramdisk问题

ubootis a large bare-board program,The bare-board program is characterized by an infinite loop,那就是main_loop,

第一个函数

main_loop

This function mainly interacts with the user,It is to parse the command entered by the user,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_loopis assigned to the array againinit_sequence_r,先看下init_sequence_rtypes and definitions,init_sequence_r 是一个函数指针数组,It is assigned the initialization function of various hardware,Take a look at the real body of this array,This array is the list of initialization functions,The functions inside are called sequentially,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,Well done.

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;

A global variable is also used in these functionsgd,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 :linuxThe entry function of the kernel

All things will eventually perish,But there will also be rebirth,uboot死亡的时候,This is where the kernel was born.

/* 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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