《uboot源码解析(三)命令行解析》
1.命令行解析
以help命令为例（~/comand/command.c）
U_BOOT_CMD( help, CFG_MAXARGS, 1, do_help, "help - print online help\n", "[command ...]\n" " - show help information (for 'command')\n" "'help' prints online help for the monitor commands.\n\n" "Without arguments, it prints a short usage message for all commands.\n\n" "To get detailed help information for specific commands you can type\n" "'help' with one or more command names as arguments.\n" );
U_BOOT_CMD里面对help命令进行了各种的描述，
#define Struct_Section __attribute__ ((unused,section (".u_boot_cmd")))
#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}
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) */
#ifdef CFG_LONGHELP
char *help; /* Help message (long) */
#endif
#ifdef CONFIG_AUTO_COMPLETE
/* do auto completion on the arguments */
int (*complete)(int argc, char *argv[], char last_char, int maxv, char *cmdv[]);
#endif
};
#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}
扩展开：
cmd_tbl_t __u_boot_cmd_help __attribute__ ((unused,section (".u_boot_cmd"))) ={
"help",
CFG_MAXARGS,
1,
do_help,
"help - print online help\n",
“后面剩下的一大段”
}
而cmd_tbl_t是一个描述命令的结构体，所以*name = “help”，maxargs = MAXARGS， repeatable = 1，int (*cmd)(struct cmd_tbl_s *, int, int, char *[]);是一个函数指针，就是int （*do_help）(struct cmd_tbl_s *, int, int, char *[])；
从上面可以看到，定义了一个结构体 cmd_tbl_t 类型的__u_boot_cmd_help，而且它的属性是：__attribute__ ((unused,section (".u_boot_cmd")))。意思是：将来链接时将这个结构体放在 uboot 的“.u_boot_cmd”段，这个段专门用来存放含有 Uboot 的命令的结构体。
u-boot.lds （~/board/smdk2410/u-boot.lds）
/*指定输出可执行文件是elf格式,32位ARM指令,小端*/ OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm") /*OUTPUT_FORMAT("elf32-arm", "elf32-arm", "elf32-arm")*/
/*指定输出可执行文件的平台为ARM*/ OUTPUT_ARCH(arm)
/*指定输出可执行文件的起始代码段为_start*/ ENTRY(_start) SECTIONS {
/*指定可执行image文件的全局入口点，通常这个地址都放在ROM(flash)0x0位置。必须使编译器知道这个地址，通常都是修改此处来完成*/ . = 0x00000000;/*;从0x0位置开始*/ . = ALIGN(4);/*代码以4字节对齐*/ .text: {
/*代码的第一个代码部分*/ cpu/arm920t/start.o (.text) *(.text) }
. = ALIGN(4); .rodata : { *(.rodata) } /*指定只读数据段*/ . = ALIGN(4); .data : { *(.data) } . = ALIGN(4); .got : { *(.got) }/*指定got段, got段是uboot自定义的一个段, 非标准段*/ . = .; __u_boot_cmd_start = .; /*把__u_boot_cmd_start赋值为当前位置, 即起始位置*/ .u_boot_cmd : { *(.u_boot_cmd) } /*指定u_boot_cmd段, uboot把所有的uboot命令放在该段.*/ __u_boot_cmd_end = .;/*把__u_boot_cmd_end赋值为当前位置,即结束位置*/ . = ALIGN(4); __bss_start = .; /*把__bss_start赋值为当前位置,即bss段的开始位置*/ .bss : { *(.bss) } _end = .;/*把_end赋值为当前位置,即bss段的结束位置*/ }
同 时 ，在 .u_boot_cmd 的 开 头 和 结 尾 各 有 一 个 标 志 __u_boot_cmd_start 和__u_boot_cmd_end ，以便于在程序中访问这个段。.u_boot_cmd在find_cmd函数中使用到
find_cmd（~/command/command.c）
/*************************************************************************** * 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 */ }
在command.h中定义
extern cmd_tbl_t __u_boot_cmd_start;
extern cmd_tbl_t __u_boot_cmd_end;
由于__u_boot_cmd_start和__u_boot_cmd_end都被声明为cmd_tbl_t类型，所以&__u_boot_cmd_start就是“.u_boot_cmd”段的第一个成员地址。通过for对.u_boot_cmd进行遍历，如果找到对应就return这个命令的结构体指针cmdtp。后续就可以用这个cmdtp去获取这个结构体里面的其他数据，包括调用相应的函数指针去执行相对应的操作。
命令行解析函数：run_command
int run_command (const char *cmd, int flag) { cmd_tbl_t *cmdtp; char cmdbuf[CFG_CBSIZE]; /* working copy of cmd */ char *token; /* start of token in cmdbuf */ char *sep; /* end of token (separator) in cmdbuf */ char finaltoken[CFG_CBSIZE]; char *str = cmdbuf; char *argv[CFG_MAXARGS + 1]; /* NULL terminated */ int argc, inquotes; int repeatable = 1; int rc = 0; #ifdef DEBUG_PARSER printf ("[RUN_COMMAND] cmd[%p]=\"", cmd); puts (cmd ? cmd : "NULL"); /* use puts - string may be loooong */ puts ("\"\n"); #endif clear_ctrlc(); /* forget any previous Control C */ if (!cmd || !*cmd) { return -1; /* empty command */ } if (strlen(cmd) >= CFG_CBSIZE) { puts ("## Command too long!\n"); return -1; } strcpy (cmdbuf, cmd); /* Process separators and check for invalid * repeatable commands */ #ifdef DEBUG_PARSER printf ("[PROCESS_SEPARATORS] %s\n", cmd); #endif while (*str) { /* * Find separator, or string end * Allow simple escape of ';' by writing "\;" */
//将多命令拆解（比如：printenv ；saveenv） for (inquotes = 0, sep = str; *sep; sep++) { if ((*sep=='\'') && (*(sep-1) != '\\')) inquotes=!inquotes; if (!inquotes && (*sep == ';') && /* separator */ ( sep != str) && /* past string start */ (*(sep-1) != '\\')) /* and NOT escaped */ break; } /* * Limit the token to data between separators */ token = str; if (*sep) { str = sep + 1; /* start of command for next pass */ *sep = '\0'; } else str = sep; /* no more commands for next pass */ #ifdef DEBUG_PARSER printf ("token: \"%s\"\n", token); #endif /* find macros in this token and replace them */
//处理字符串中的转义字符 process_macros (token, finaltoken); /* Extract arguments */
//解析命令（比如md.w 0这个字符串就会解析成argv[0]="md.w" argv=[1]="0"） if ((argc = parse_line (finaltoken, argv)) == 0) { rc = -1; /* no command at all */ continue; } /* Look up command in command table */
//根据argv[0]，然后进行对比。找出相对应的命令，执行相对应得函数 if ((cmdtp = find_cmd(argv[0])) == NULL) { printf ("Unknown command '%s' - try 'help'\n", argv[0]); rc = -1; /* give up after bad command */ continue; } /* found - check max args */ if (argc > cmdtp->maxargs) { printf ("Usage:\n%s\n", cmdtp->usage); rc = -1; continue; } #if (CONFIG_COMMANDS & CFG_CMD_BOOTD) /* avoid "bootd" recursion */ if (cmdtp->cmd == do_bootd) { #ifdef DEBUG_PARSER printf ("[%s]\n", finaltoken); #endif if (flag & CMD_FLAG_BOOTD) { puts ("'bootd' recursion detected\n"); rc = -1; continue; } else { flag |= CMD_FLAG_BOOTD; } } #endif /* CFG_CMD_BOOTD */ /* OK - call function to do the command */
//调用函数指针执行相对应的操作 if ((cmdtp->cmd) (cmdtp, flag, argc, argv) != 0) { rc = -1; } repeatable &= cmdtp->repeatable; /* Did the user stop this? */ if (had_ctrlc ()) return 0; /* if stopped then not repeatable */ } return rc ? rc : repeatable; }
