/********************************************************************************/
u-boot命令尋找分析
/***************************************************************************
 * find command table entry for a command
 */
cmd_tbl_t *find_cmd (const char *cmd)
{
	cmd_tbl_t *cmdtp;
	cmd_tbl_t *cmdtp_temp = &
 
__u_boot_cmd_start;	/*Init value */
	const char *p;
	int len;
	int n_found = 0;

	/*
	 * Some commands allow length modifiers (like "cp.b");
	 * compare command name only until first dot.
	 */
	len = ((p = strchr(cmd, '.')) == NULL) ? strlen (cmd) : (p - cmd);

	for (cmdtp = &__u_boot_cmd_start;
	     cmdtp !=
 
 &__u_boot_cmd_end;
	     cmdtp++) {
		if (strncmp (cmd, cmdtp->name, len) == 0) {
			if (len == strlen (cmdtp->name))
				return cmdtp;	/* full match */

			cmdtp_temp = cmdtp;	/* abbreviated command ? */
			n_found++;
		}
	}
	if (n_found == 1) {			/* exactly one match */
		return cmdtp_temp;
	}
 


	return NULL;	/* not found or ambiguous command */
}

	for (cmdtp = &__u_boot_cmd_start;
	     cmdtp != &__u_boot_cmd_end;
	     cmdtp++)

		 
u-boot.lds的連結指令碼之中也能傳遞變數		 
SECTIONS
{
	. = 0x00000000;

	. = ALIGN(4);
	.text      :
	{
	  cpu/arm920t/start.o	(.text)
          board/100ask24x0/boot_init.o (.text)
	  *(.text)
	}

	. = ALIGN(4);
	.rodata : { *(.rodata) }

	. = ALIGN(4);
	.data : { *(.data) }

	. = ALIGN(4);
	.got : { *(.got) }

	. = .;
	__u_boot_cmd_start = .;
	.u_boot_cmd : { *(.u_boot_cmd) }
	__u_boot_cmd_end = .;

	. = ALIGN(4);
	__bss_start = .;
	.bss : { *(.bss) }
	_end = .;
}
		 
		 

#define Struct_Section  __attribute__ ((unused,section (".u_boot_cmd")))

#ifdef  CFG_LONGHELP

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

#else	/* no long help info */


rep命令代表的是命令是否可重複
#define U_BOOT_CMD(name,maxargs,rep,cmd,usage,help) \
cmd_tbl_t __u_boot_cmd_##name Struct_Section = {#name, maxargs, rep, cmd, usage}		 
		 
		 
nand read.jffs2 0x30007FC0 kernel; bootm 0x30007FC0		 
U_BOOT_CMD(
 	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
);
		 
cmd_tbl_t __u_boot_cmd_bootm __attribute__ ((unused,section (".u_boot_cmd"))) = 
{"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"}
在巨集定義中  #是轉化為字串的意思
下面這句的意思是設定該結構體段屬性為.u_boot_cmd
cmd_tbl_t __u_boot_cmd_bootm __attribute__ ((unused,section (".u_boot_cmd"))) 
因此只要是定義為  U_BOOT_CMD 型別的結構體都將被強制轉化為 段的屬性為  .u_boot_cmd     該屬性在連結指令碼中定義了
因此在find_cmd中能夠使用 
for (cmdtp = &__u_boot_cmd_start;
	     cmdtp != &__u_boot_cmd_end;
	     cmdtp++)
按照結構體的形式將命令挨個找出來