U_BOOT_CMD命令的实现

宏定义，用于定义一个U_BOOT命令

#define U_BOOT_CMD(name,maxargs,rep,cmd,usage) /
cmd_tbl_t __u_boot_cmd_##name Struct_Section = {#name, maxargs, rep, cmd, usage}

#define Struct_Section  __attribute__ ((unused,section (".u_boot_cmd")))//设置属性，存在.u_boot_cmd段中

Struct cmd_tbl_s:

struct cmd_tbl_s {
char        *name;      /* Command Name         */
int     maxargs;        /* maximum number of arguments  */
int     repeatable;     /* autorepeat allowed?      */
/* Implementation function  */
int     (*cmd)(struct cmd_tbl_s *, int, int, char *[]);
char        *usage;     /* Usage message    (short) */
char        *help;      /* Help  message    (long)  */
#ifdef CONFIG_AUTO_COMPLETE
/* do auto completion on the arguments */
int     (*complete)(int argc, char *argv[], char last_char, int maxv, char *cmdv[]);
#endif
};

typedef struct cmd_tbl_s    cmd_tbl_t;

例如：

U_BOOT_CMD(
bootm, CONFIG_SYS_MAXARGS, 1, do_bootm,
"boot application image from memory", bootm_help_text
);展开后：
cmd_tbl_t __u_boot_cmd_##namebootm Struct_Section__attribute__ ((unused,section (".u_boot_cmd"))) =
{#name"bootm", maxargs16, rep1, cmddo_bootm, usage"boot application image from memory"}