从头理清uboot（4）-boot_cmd 的处理

1. 默认的bootcmd 包含了哪些内容？
2. boot-linux 函数过程
3. 一些指令是如何实现的?

上次我们分析到，uboot在启动linux的过程中，最后是执行bootcmd这个环境变量，那么我们今天来分析，这个环境变量到底执行了哪些功能，这些功能调用了哪些函数，最后是如何实现linux的boot的？

关于环境变量：对于imax6ull来说，都是存储在/include/configs/mx6ullevk.h和include/env_dedault.h

1. 默认的bootcmd 包含了哪些内容？

在default_environment中有定义：于是查找CONFIG_BOOTCOMMAND

 #ifdef	CONFIG_BOOTCOMMAND
	"bootcmd="	CONFIG_BOOTCOMMAND		"\0"
#endif

在./include/configs/mx6ullevk.h中有定义：

 #define CONFIG_BOOTCOMMAND \
	   "run findfdt;" \
	   "mmc dev ${mmcdev};" \
	   "mmc dev ${mmcdev}; if mmc rescan; then " \
		   "if run loadbootscript; then " \
			   "run bootscript; " \
		   "else " \
			   "if run loadimage; then " \
				   "run mmcboot; " \
			   "else run netboot; " \
			   "fi; " \
		   "fi; " \
	   "else run netboot; fi"
#endif

其中,有以下环境变量：

findfdt：其中会用到fdt_file=undefined，board_name=EVK，board_rev=14X14 这三个变量，用于寻找.dtb 文件

 	"findfdt="\
			"if test $fdt_file = undefined; then " \
				"if test $board_name = EVK && test $board_rev = 9X9; then " \
					"setenv fdt_file imx6ull-9x9-evk.dtb; fi; " \
				"if test $board_name = EVK && test $board_rev = 14X14; then " \
					"setenv fdt_file imx6ull-14x14-evk.dtb; fi; " \
				"if test $fdt_file = undefined; then " \
					"echo WARNING: Could not determine dtb to use; fi; " \
			"fi;\0" \

mmc dev ${mmcdev} : 用于切换mmc 设置mmc 设备
mmc rescan ：执行mmc 扫描检查，成功执行run loadbootscript失败就执行run netboot网络boot。
run loadbootscript ：
```
 	"loadbootscript=" \
		"fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${script};\0" \
```
其中 mmcdev=1，mmcpart=1，loadaddr=0x80800000，script= boot.scr因此展开之后为下面指令，就是从 mmc1 的分区 1 中读取文件 boot.src 到 DRAM 的 0X80800000 处，如果成功的话就执行bootscript不行就会执行run loadimage
```
 loadbootscript=fatload mmc 1:1 0x80800000 boot.scr; 
```
- bootscript：只是一个输出语句
```
 "bootscript=echo Running bootscript from mmc ...; " \
```

run loadimage：见下方注释为从mmc 加载zImage到0x80800000地址处。

 "loadimage=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${image}\0" \
  /* 其中：  mmcdev=1、mmcpart=1  loadaddr=0x80800000、image = zImage 所以展开之后就是：*/ 
    loadimage=fatload mmc 1:1 0x80800000 zImage

1.1 mmcboot

mmcboot 的源码如下：

 	"mmcboot=echo Booting from mmc ...; " \
		"run mmcargs; " \
		"if test ${boot_fdt} = yes || test ${boot_fdt} = try; then " \
			"if run loadfdt; then " \
				"bootz ${loadaddr} - ${fdt_addr}; " \
			"else " \
				"if test ${boot_fdt} = try; then " \
  				"bootz; " \
				"else " \
  				"echo WARN: Cannot load the DT; " \
				"fi; " \
			"fi; " \
		"else " \
			"bootz; " \
		"fi;\0" \

其中第一行是设置boot 参数

   	"mmcargs=setenv bootargs console=${console},${baudrate} " \
		CONFIG_BOOTARGS_CMA_SIZE \
  		CONFIG_MFG_NAND_PARTITION \
  		"root=${mmcroot}\0" \
   /*"console=ttymxc"  baudrate=115200  mmcroot="/dev/mmcblk1p2"rootwait rw */ 
   所以这句话为：
  mmcargs=setenv bootargs  console=ttymxc0,115200  "" "" root=/dev/mmcblk1p2 rootwait rw

由于"boot_fdt=try\0" \所以执行loadfdt,由于fdt_file在之前findfdt时候初始化过了，所以额这里就是load dtb 文件到0x83000000。

 "loadfdt=fatload mmc ${mmcdev}:${mmcpart} ${fdt_addr} ${fdt_file}\0" \
 /* mmcdev=1、mmcpart=1 fdt_addr=0x83000000 、fdt_file= imx6ull-14x14-evk.dtb \0 */
    fatload mmc 1:1 0x83000000 imx6ull-14x14-evk.dtb

  
* 于是` run loadfdt`执行成功，就会执行指令：
 
  ```c
  bootz ${loadaddr} - ${fdt_addr};
  /* loadaddr =  0x80800000  fdt_addr=0x83000000*/
  bootz 0x80800000 - 0x83000000

1.2 netboot

 		"netboot=echo Booting from net ...; " \
		"run netargs; " \
		"if test ${ip_dyn} = yes; then " \
			"setenv get_cmd dhcp; " \
		"else " \
			"setenv get_cmd tftp; " \
		"fi; " \
		"${get_cmd} ${image}; " \
		"if test ${boot_fdt} = yes || test ${boot_fdt} = try; then " \
			"if ${get_cmd} ${fdt_addr} ${fdt_file}; then " \
				"bootz ${loadaddr} - ${fdt_addr}; " \
			"else " \
				"if test ${boot_fdt} = try; then " \
					"bootz; " \
				"else " \
					"echo WARN: Cannot load the DT; " \
				"fi; " \
			"fi; " \
		"else " \
			"bootz; " \
		"fi;\0" \

1.3 小总结

对于mmc_boot有效的信息如下：
1. 给findfdt赋值，设置dtb文件：setenv fdt_file imx6ull-14x14-evk.dtb
2. 设置mmc 设备: mmc dev 1
3. 加载镜像：fatload mmc 1:1 0x80800000 zImage
4. 设置bootargs：setenv bootargs console=ttymxc0,115200 "" "" root=/dev/mmcblk1p2 rootwait rw
5. 加载dtb：fatload mmc 1:1 0x83000000 imx6ull-14x14-evk.dtb
6. 启动：bootz 0x80800000 - 0x83000000

1.4 关于`bootargs`

bootargs 是uboot 传递给linux 中的参数，上述解析之后的参数见下方：
```
 mmcargs=setenv bootargs  console=ttymxc0,115200  "" "" root=/dev/mmcblk1p2 rootwait rw
```
其中有三个设置点：
1. console ：设置Linux的输出窗口，由于mx6ull中，串口0的表示是/dev/ttymxc0所以设置输出窗口为这个。
2. root ：设置根文件系统的位置，告诉Linux在哪里寻找根文件系统。/dev/mmcblk1p2 表示在ima6ull的分区2中。后续还有“rootwait rw”数据，表示等待根文件系统挂载完毕才加载，rw表示文件系统是可读写的。

2. boot-linux 函数过程

上面分析到，在把image和dtb 搬运到固定地址之后，执行bootz 0x80800000 - 0x83000000指令，进入linux 的boot 阶段。bootz指令的定义如下，于是可以发现是执行do_bootz函数。

 U_BOOT_CMD(
	bootz,	CONFIG_SYS_MAXARGS,	1,	do_bootz,
	"boot Linux zImage image from memory", bootz_help_text
);

2.1 结构体简单介绍

uboot 中定义了bootm_headers_t和image_header_t结构体分别用来抽象image 信息和 image 头部信息。

 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;
    #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
} bootm_headers_t;
 
extern bootm_headers_t images;
 
 
/* 其中，header 再定义为： */
 typedef struct image_header {
	__be32		ih_magic;	/* Image Header Magic Number	*/
	__be32		ih_hcrc;	/* Image Header CRC Checksum	*/
	__be32		ih_time;	/* Image Creation Timestamp	*/
	__be32		ih_size;	/* Image Data Size		*/
	__be32		ih_load;	/* Data	 Load  Address		*/
	__be32		ih_ep;		/* Entry Point Address		*/
	__be32		ih_dcrc;	/* Image Data CRC Checksum	*/
	uint8_t		ih_os;		/* Operating System		*/
	uint8_t		ih_arch;	/* CPU architecture		*/
	uint8_t		ih_type;	/* Image Type			*/
	uint8_t		ih_comp;	/* Compression Type		*/
	uint8_t		ih_name[IH_NMLEN];	/* Image Name		*/
} image_header_t;

2.2 do_bootz函数分析

do_bootz会调用bootz_start准备好环境之后，关闭中断，在设置要启动的系统是IH_OS_LINUX之后，就会利用do_bootm_states函数启动linux。源码如下：

 int do_bootz(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
	int ret;
	/* Consume 'bootz'  过滤掉bootz 参数，这样子addr= argv[0] */ 
	argc--; argv++;
	if (bootz_start(cmdtp, flag, argc, argv, &images))
		return 1;
 
    bootm_disable_interrupts();
	
    images.os.os = IH_OS_LINUX;
	ret = do_bootm_states(cmdtp, flag, argc, argv,
			      BOOTM_STATE_OS_PREP | BOOTM_STATE_OS_FAKE_GO |
			      BOOTM_STATE_OS_GO,
			      &images, 1);
 
	return ret;
}

2.2.1 bootz_start 函数

见下方，bootz_start的主要功能为：

调用 do_bootm_states,且把状态设置为 BOOTM_STATE_START 准备环境，释放原来images占用的区域。
设置images->ep这个地址是image 的启动地址（entry-point）。
把images->ep头部指针传递给bootz_setup,在里面会做是否是linux 系统image 的判定，并且获得起始和结束位置，如果不是的话会报错，给image 指针重定位。
调用lmb_reserve将image 占用的内存大小和区域设置为已经使用的区域。
调用bootm_find_images去找到dtb 文件，并且将地址和长度信息，存储到全局变量images中。

做完以上之后，就会调用do_bootm_states,并且设置对应状态启动inux。

 static int bootz_start(cmd_tbl_t *cmdtp, int flag, int argc,
			char * const argv[], bootm_headers_t *images)
{
	int ret;
	ulong zi_start, zi_end;
	ret = do_bootm_states(cmdtp, flag, argc, argv, BOOTM_STATE_START,
			      images, 1); /* */
 
	/* Setup Linux kernel zImage entry point */
	if (!argc) {
		images->ep = load_addr;
		debug("*  kernel: default image load address = 0x%08lx\n",
				load_addr);
	} else {
		images->ep = simple_strtoul(argv[0], NULL, 16);
		debug("*  kernel: cmdline image address = 0x%08lx\n",
			images->ep);
	}
 
	ret = bootz_setup(images->ep, &zi_start, &zi_end);
	if (ret != 0)
		return 1;
 
	lmb_reserve(&images->lmb, images->ep, zi_end - zi_start);
 
	if (bootm_find_images(flag, argc, argv))
		return 1;
	return 0;
}

2.2.2 do_bootm_states 函数

do_bootm_states 能够根据不同的状态执行不同的函数，在imax6ull 中，起到了下面这些作用：

调用bootm_start函数，释放原来images指向的区域并清0。
调用bootm_load_os函数，设置对应的地址。
调用bootm_os_get_boot_func函数:找到boot 中真正使用的函数。本次boot 的os 在之前已经设置过了为IH_OS_LINUX于是会调用do_bootm_linux。后面执行的boot_fn(BOOTM_STATE_OS_CMDLINE, argc, argv, images);函数实际上都是由do_bootm_linux函数执行。

 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);
		argc = 0;	/* consume the args */
	}
    ......
        
    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);
	......
    	/*  这里实际执行的都是do_bootm_linux 函数了！ */
    	/* 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))
		ret = boot_fn(BOOTM_STATE_OS_PREP, argc, argv, images);
	......
    	/* 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);
}

2.2.3 do_bootm_linux函数

上面说到，在本次启动过程中，最后实际调用的是do_bootm_linux于是再继续分析这个函数。

我们在do_bootz的时候，实际调用的是这调用整个宏BOOTM_STATE_OS_PREP ，会调用boot_prep_linux(images); 这个函数进行启动前的准备。

 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;
}

后面do_bootz会调用boot_selected_os函数，之后继续调用do_bootm_linux并且将flag 设置为BOOTM_STATE_OS_GO，执行boot_jump_linux(images, flag);

 boot_selected_os(argc, argv, BOOTM_STATE_OS_GO,
				images, boot_fn);
/* 实际还是调用了  boot_fn(state, argc, argv, images); */
/* 在bootlinux 的情况下，实际执行的是：do_bootm_linux*/
 do_bootm_linux (BOOTM_STATE_OS_GO,argc,argv，images)

2.2.4 boot_jump_linux函数

可见boot_jump_linux的作用如下：

定义函数指针并且赋值为images->ep,作为程序跳转到linux 的入口。
获取id值和环境变量machid比较，判断是否相等。
清除CPU的cache 环境。
设置函数指针kernel_entry的参数，分别是0、machid、fdt地址/或者bi_boot_params。如果不使用设备数的话，就是bootargs

 /* Subcommand: GO */
static void boot_jump_linux(bootm_headers_t *images, int flag)
{
	unsigned long machid = gd->bd->bi_arch_number;
	char *s;
	void (*kernel_entry)(int zero, int arch, uint params);/* 定义函数指针 */
	unsigned long r2;
	int fake = (flag & BOOTM_STATE_OS_FAKE_GO);
 
	kernel_entry = (void (*)(int, int, uint))images->ep; /*给函数指针赋值为*/
 
	s = getenv("machid");    /* 比较id 是不是和环境变量是相同的 */
	if (s) {
		if (strict_strtoul(s, 16, &machid) < 0) {
			debug("strict_strtoul failed!\n");
			return;
		}
		printf("Using machid 0x%lx from environment\n", machid);
	}
 
	debug("## Transferring control to Linux (at address %08lx)" \
		"...\n", (ulong) kernel_entry);
	bootstage_mark(BOOTSTAGE_ID_RUN_OS);
	announce_and_cleanup(fake);					/* CPU clean up,把cache 都刷掉了。 */
 
	if (IMAGE_ENABLE_OF_LIBFDT && images->ft_len)/* 把 r2 寄存器设置为ft_addr 或者 bi_boot_params*/
		r2 = (unsigned long)images->ft_addr;
	else
		r2 = gd->bd->bi_boot_params;
 
	if (!fake) {
#ifdef CONFIG_ARMV7_NONSEC
		if (armv7_boot_nonsec()) {
			armv7_init_nonsec();
			secure_ram_addr(_do_nonsec_entry)(kernel_entry,
							  0, machid, r2);
		} else
#endif
			kernel_entry(0, machid, r2);
	}
#endif
}

小问题，之前提到的bootargs 是在哪里设定的呢，怎么传递过去的？
- 如果不适用fdt的话，参数r2 就是bootargs的值。

3. 一些指令是如何实现的?

由前面分析我们可以知道，uboot 的命令都是由U_BOOT_CMD实现的，所以我们可以在boot 的文件夹下搜索我们关心的命令，例如上面频繁的用到了fatload命令，我们可以搜索如下：

 :~/for_study/imax6ull/uboot$: grep  -nr "U_BOOT_CMD" | grep -n "fat"
    
/* 得到下面结果 */
1244:cmd/fat.c:27:U_BOOT_CMD(
1245:cmd/fat.c:41:U_BOOT_CMD(
1246:cmd/fat.c:61:U_BOOT_CMD(
1247:cmd/fat.c:93:U_BOOT_CMD(
1248:cmd/fat.c:145:U_BOOT_CMD(

可以发现，是在这些命令都在cmd/fat.c里面，由此可以找到命令的定义和回调函数，具体的实现就需要深入研究源码了。

 U_BOOT_CMD(
	fatload,	7,	0,	do_fat_fsload,
	......
	}

上一篇从头理清uboot（3）-main_loop 及 CMD实现

本文作者：Satellite98

本文链接：https://www.cnblogs.com/satellite98/p/18329105

posted @ 2024-07-28 22:58 Satellite98 阅读(323) 评论(0) 编辑收藏举报

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satellite98

从头理清uboot（4）-boot_cmd 的处理

1. 默认的bootcmd 包含了哪些内容？

1.1 mmcboot

1.2 netboot

1.3 小总结

1.4 关于`bootargs`

2. boot-linux 函数过程

2.1 结构体简单介绍

2.2 do_bootz函数分析

2.2.1 bootz_start 函数

2.2.2 do_bootm_states 函数

2.2.3 do_bootm_linux函数

2.2.4 boot_jump_linux函数

3. 一些指令是如何实现的?

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	#ifdef CONFIG_BOOTCOMMAND
	"bootcmd=" CONFIG_BOOTCOMMAND "\0"
	#endif

	#define CONFIG_BOOTCOMMAND \
	"run findfdt;" \
	"mmc dev ${mmcdev};" \
	"mmc dev ${mmcdev}; if mmc rescan; then " \
	"if run loadbootscript; then " \
	"run bootscript; " \
	"else " \
	"if run loadimage; then " \
	"run mmcboot; " \
	"else run netboot; " \
	"fi; " \
	"fi; " \
	"else run netboot; fi"
	#endif

	"findfdt="\
	"if test $fdt_file = undefined; then " \
	"if test $board_name = EVK && test $board_rev = 9X9; then " \
	"setenv fdt_file imx6ull-9x9-evk.dtb; fi; " \
	"if test $board_name = EVK && test $board_rev = 14X14; then " \
	"setenv fdt_file imx6ull-14x14-evk.dtb; fi; " \
	"if test $fdt_file = undefined; then " \
	"echo WARNING: Could not determine dtb to use; fi; " \
	"fi;\0" \

	"loadbootscript=" \
	"fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${script};\0" \

	"loadimage=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${image}\0" \
	/* 其中： mmcdev=1、mmcpart=1 loadaddr=0x80800000、image = zImage 所以展开之后就是：*/
	loadimage=fatload mmc 1:1 0x80800000 zImage

	"mmcboot=echo Booting from mmc ...; " \
	"run mmcargs; " \
	"if test ${boot_fdt} = yes \|\| test ${boot_fdt} = try; then " \
	"if run loadfdt; then " \
	"bootz ${loadaddr} - ${fdt_addr}; " \
	"else " \
	"if test ${boot_fdt} = try; then " \
	"bootz; " \
	"else " \
	"echo WARN: Cannot load the DT; " \
	"fi; " \
	"fi; " \
	"else " \
	"bootz; " \
	"fi;\0" \

	"mmcargs=setenv bootargs console=${console},${baudrate} " \
	CONFIG_BOOTARGS_CMA_SIZE \
	CONFIG_MFG_NAND_PARTITION \
	"root=${mmcroot}\0" \
	/"console=ttymxc" baudrate=115200 mmcroot="/dev/mmcblk1p2"rootwait rw /
	所以这句话为：
	mmcargs=setenv bootargs console=ttymxc0,115200 "" "" root=/dev/mmcblk1p2 rootwait rw

	"loadfdt=fatload mmc ${mmcdev}:${mmcpart} ${fdt_addr} ${fdt_file}\0" \
	/* mmcdev=1、mmcpart=1 fdt_addr=0x83000000 、fdt_file= imx6ull-14x14-evk.dtb \0 */
	fatload mmc 1:1 0x83000000 imx6ull-14x14-evk.dtb


	* 于是` run loadfdt`执行成功，就会执行指令：

	```c
	bootz ${loadaddr} - ${fdt_addr};
	/* loadaddr = 0x80800000 fdt_addr=0x83000000*/
	bootz 0x80800000 - 0x83000000

	"netboot=echo Booting from net ...; " \
	"run netargs; " \
	"if test ${ip_dyn} = yes; then " \
	"setenv get_cmd dhcp; " \
	"else " \
	"setenv get_cmd tftp; " \
	"fi; " \
	"${get_cmd} ${image}; " \
	"if test ${boot_fdt} = yes \|\| test ${boot_fdt} = try; then " \
	"if ${get_cmd} ${fdt_addr} ${fdt_file}; then " \
	"bootz ${loadaddr} - ${fdt_addr}; " \
	"else " \
	"if test ${boot_fdt} = try; then " \
	"bootz; " \
	"else " \
	"echo WARN: Cannot load the DT; " \
	"fi; " \
	"fi; " \
	"else " \
	"bootz; " \
	"fi;\0" \

	U_BOOT_CMD(
	bootz, CONFIG_SYS_MAXARGS, 1, do_bootz,
	"boot Linux zImage image from memory", bootz_help_text
	);

	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;
	#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
	} bootm_headers_t;

	extern bootm_headers_t images;


	/* 其中，header 再定义为： */
	typedef struct image_header {
	__be32 ih_magic; /* Image Header Magic Number */
	__be32 ih_hcrc; /* Image Header CRC Checksum */
	__be32 ih_time; /* Image Creation Timestamp */
	__be32 ih_size; /* Image Data Size */
	__be32 ih_load; /* Data Load Address */
	__be32 ih_ep; /* Entry Point Address */
	__be32 ih_dcrc; /* Image Data CRC Checksum */
	uint8_t ih_os; /* Operating System */
	uint8_t ih_arch; /* CPU architecture */
	uint8_t ih_type; /* Image Type */
	uint8_t ih_comp; /* Compression Type */
	uint8_t ih_name[IH_NMLEN]; /* Image Name */
	} image_header_t;

	int do_bootz(cmd_tbl_t cmdtp, int flag, int argc, char const argv[])
	{
	int ret;
	/* Consume 'bootz' 过滤掉bootz 参数，这样子addr= argv[0] */
	argc--; argv++;
	if (bootz_start(cmdtp, flag, argc, argv, &images))
	return 1;

	bootm_disable_interrupts();

	images.os.os = IH_OS_LINUX;
	ret = do_bootm_states(cmdtp, flag, argc, argv,
	BOOTM_STATE_OS_PREP \| BOOTM_STATE_OS_FAKE_GO \|
	BOOTM_STATE_OS_GO,
	&images, 1);

	return ret;
	}

	static int bootz_start(cmd_tbl_t *cmdtp, int flag, int argc,
	char * const argv[], bootm_headers_t *images)
	{
	int ret;
	ulong zi_start, zi_end;
	ret = do_bootm_states(cmdtp, flag, argc, argv, BOOTM_STATE_START,
	images, 1); /* */

	/* Setup Linux kernel zImage entry point */
	if (!argc) {
	images->ep = load_addr;
	debug("* kernel: default image load address = 0x%08lx\n",
	load_addr);
	} else {
	images->ep = simple_strtoul(argv[0], NULL, 16);
	debug("* kernel: cmdline image address = 0x%08lx\n",
	images->ep);
	}

	ret = bootz_setup(images->ep, &zi_start, &zi_end);
	if (ret != 0)
	return 1;

	lmb_reserve(&images->lmb, images->ep, zi_end - zi_start);

	if (bootm_find_images(flag, argc, argv))
	return 1;
	return 0;
	}

	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);
	argc = 0; /* consume the args */
	}
	......

	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);
	......
	/* 这里实际执行的都是do_bootm_linux 函数了！ */
	/* 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))
	ret = boot_fn(BOOTM_STATE_OS_PREP, argc, argv, images);
	......
	/* 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);
	}

	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;
	}

	boot_selected_os(argc, argv, BOOTM_STATE_OS_GO,
	images, boot_fn);
	/* 实际还是调用了 boot_fn(state, argc, argv, images); */
	/* 在bootlinux 的情况下，实际执行的是：do_bootm_linux*/
	do_bootm_linux (BOOTM_STATE_OS_GO,argc,argv，images)

	/* Subcommand: GO */
	static void boot_jump_linux(bootm_headers_t *images, int flag)
	{
	unsigned long machid = gd->bd->bi_arch_number;
	char *s;
	void (kernel_entry)(int zero, int arch, uint params);/ 定义函数指针 */
	unsigned long r2;
	int fake = (flag & BOOTM_STATE_OS_FAKE_GO);

	kernel_entry = (void ()(int, int, uint))images->ep; /给函数指针赋值为*/

	s = getenv("machid"); /* 比较id 是不是和环境变量是相同的 */
	if (s) {
	if (strict_strtoul(s, 16, &machid) < 0) {
	debug("strict_strtoul failed!\n");
	return;
	}
	printf("Using machid 0x%lx from environment\n", machid);
	}

	debug("## Transferring control to Linux (at address %08lx)" \
	"...\n", (ulong) kernel_entry);
	bootstage_mark(BOOTSTAGE_ID_RUN_OS);
	announce_and_cleanup(fake); /* CPU clean up,把cache 都刷掉了。 */

	if (IMAGE_ENABLE_OF_LIBFDT && images->ft_len)/* 把 r2 寄存器设置为ft_addr 或者 bi_boot_params*/
	r2 = (unsigned long)images->ft_addr;
	else
	r2 = gd->bd->bi_boot_params;

	if (!fake) {
	#ifdef CONFIG_ARMV7_NONSEC
	if (armv7_boot_nonsec()) {
	armv7_init_nonsec();
	secure_ram_addr(_do_nonsec_entry)(kernel_entry,
	0, machid, r2);
	} else
	#endif
	kernel_entry(0, machid, r2);
	}
	#endif
	}

	:~/for_study/imax6ull/uboot$: grep -nr "U_BOOT_CMD" \| grep -n "fat"

	/* 得到下面结果 */
	1244:cmd/fat.c:27:U_BOOT_CMD(
	1245:cmd/fat.c:41:U_BOOT_CMD(
	1246:cmd/fat.c:61:U_BOOT_CMD(
	1247:cmd/fat.c:93:U_BOOT_CMD(
	1248:cmd/fat.c:145:U_BOOT_CMD(

satellite98

从头理清uboot（4）-boot_cmd 的处理

1. 默认的bootcmd 包含了哪些内容？

1.1 mmcboot

1.2 netboot

1.3 小总结

1.4 关于bootargs

2. boot-linux 函数过程

2.1 结构体简单介绍

2.2 do_bootz函数分析

2.2.1 bootz_start 函数

2.2.2 do_bootm_states 函数

2.2.3 do_bootm_linux函数

2.2.4 boot_jump_linux函数

3. 一些指令是如何实现的?

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1.4 关于`bootargs`