启动参数处理

/* Untouched command line saved by arch-specific code. */
char __initdata boot_command_line[COMMAND_LINE_SIZE];
/* Untouched saved command line (eg. for /proc) */
char *saved_command_line;
/* Command line for parameter parsing */
static char *static_command_line;

#define COMMAND_LINE_SIZE  1024
#define CONFIG_CMDLINE "console=ttySAC0 root=/dev/mtdblock2 rootfstype=cramfs init=/linuxrc"

/*may overwritten in parse_tag_cmdline(const struct tag *tag)*/
static char default_command_line[COMMAND_LINE_SIZE] __initdata = CONFIG_CMDLINE;
static char __initdata cmd_line[COMMAND_LINE_SIZE];

asmlinkage void __init start_kernel(void)
    -->char * command_line;
    -->setup_arch(&command_line); //setup_arch(char ** cmdline_p)
        -->char *from = default_command_line;
        -->parse_cmdline(cmdline_p, from);

static void __init parse_cmdline(char **cmdline_p, char *from)
{
    char c = ‘ ‘, *to = command_line;
    int len = 0;
    for (;;) {
        if (c == ‘ ‘) {
            extern struct early_params __early_begin, __early_end;
            struct early_params *p;

            for (p = &__early_begin; p < &__early_end; p++) {
                int len = strlen(p->arg);

                if (memcmp(from, p->arg, len) == 0) {
                    if (to != command_line)
                        to -= 1;
                    from += len;
                    p->fn(&from);

                    while (*from != ‘ ‘ && *from != ‘\0‘)
                        from++;
                    break;
                }
            }
        }
        c = *from++;
        if (!c)
            break;
        if (COMMAND_LINE_SIZE <= ++len)
            break;
        *to++ = c;
    }
    *to = ‘\0‘;
    *cmdline_p = command_line;
}

/*
 * Early command line parameters.
 */
struct early_params {
    const char *arg;
    void (*fn)(char **p);
};

#define __early_param(name,fn)                    static struct early_params __early_##fn __used            __attribute__((__section__(".early_param.init"))) = { name, fn }