#define U_BOOT_CMD(name,maxargs,rep,cmd,usage,help) \
cmd_tbl_t __u_boot_cmd_##name Struct_Section = {#name, maxargs, rep, cmd, usage}
其中：
- name：命令的名字，他不是一个字符串，不能用双引号括起来
- maxargs：最大的参数个数
- command：对应的函数指针
- usage：一个字符串，简短的使用说明
- help：一个字符串，比较详细的使用说明
对于bootm命令，其定义如下：
- U_BOOT_CMD(//bootm命令
- bootm, CFG_MAXARGS, 1, do_bootm,
- "bootm - boot application image from memory\n",
- "[addr [arg ...]]\n - boot application image stored in memory\n"
- "\tpassing arguments 'arg ...'; when booting a Linux kernel,\n"
- "\t'arg' can be the address of an initrd image\n"
- #ifdef CONFIG_OF_FLAT_TREE
- "\tWhen booting a Linux kernel which requires a flat device-tree\n"
- "\ta third argument is required which is the address of the of the\n"
- "\tdevice-tree blob. To boot that kernel without an initrd image,\n"
- "\tuse a '-' for the second argument. If you do not pass a third\n"
- "\ta bd_info struct will be passed instead\n"
- #endif
- );
U_BOOT_CMD(//bootm命令
bootm, CFG_MAXARGS, 1, do_bootm,
"bootm - boot application image from memory\n",
"[addr [arg ...]]\n - boot application image stored in memory\n"
"\tpassing arguments 'arg ...'; when booting a Linux kernel,\n"
"\t'arg' can be the address of an initrd image\n"
#ifdef CONFIG_OF_FLAT_TREE
"\tWhen booting a Linux kernel which requires a flat device-tree\n"
"\ta third argument is required which is the address of the of the\n"
"\tdevice-tree blob. To boot that kernel without an initrd image,\n"
"\tuse a '-' for the second argument. If you do not pass a third\n"
"\ta bd_info struct will be passed instead\n"
#endif
);
bootm命令是用来引导经过U-Boot的工具mkimage打包后的kernel image的。U-Boot源代码的tools/目录下有mkimage工具，这个工具可以用来制作不压缩或者压缩的多种可启动映象文件。
mkimage在制作映象文件的时候，是在原来的可执行映象文件的前面加上一个0x40字节的头，记录参数所指定的信息，这样uboot才能识别这个映象是针对哪个CPU体系结构的，哪个OS的，哪种类型，加载内存中的哪个位置， 入口点在内存的那个位置以及映象名是什么。
U-Boot正是通过bootm命令引导Linux内核的。bootm命令调用do_bootm函数，下面我们来分析一下：
![]()
do_bootm函数流程分析
![]()
do_bootm_linux函数
