如图所示，在include/asm-arm/arch.h中找到了定义的结构体类型machine_desc，并且在代码中它的段属性被强制定义成了.arch.info.init。这样做的目的是在刚刚我们看到的vmlinux.lds链接脚本文件中，可以将具有.arch.info.init段属性的结构体统一放在__arch_info_begin和__arch_info_end之间。非常便于处理。那么现在我们将这个结构体展开，看看它的内容。也就是将arch/arm/mach-s3c2440中的参数传入。展开后如下：
#define MACHINE_START(_type,_name) \ static const struct machine_desc __mach_desc_S3C2440 \ __used \ __attribute__((__section__(".arch.info.init"))) = { \ .nr = MACH_TYPE_S3C2440, \ .name = "SMDK2440", /* Maintainer: Ben Dooks <ben@fluff.org> */ .phys_io = S3C2410_PA_UART, .io_pg_offst = (((u32)S3C24XX_VA_UART) >> 18) & 0xfffc, .boot_params = S3C2410_SDRAM_PA + 0x100, //0x30000100 .init_irq = s3c24xx_init_irq, .map_io = smdk2440_map_io, .init_machine = smdk2440_machine_init, .timer = &s3c24xx_timer, };
现在我们看到，定义的结构体类型machine_desc，内容为.nr到.timer。我们可以看出这个结构体大概是存储硬件信息。nr存放机器ID，name存放单板名称，phys_io存放输入输出口，io_pg_offst存放IO的偏移地址，boot_params存放uboot传给内核的启动参数（TAG）,init_irq存放的是中断初始化信息，map_io为IO的映射表，init_machine存放的是单板的初始化信息，timer存放的是单板的定时器信息。
struct machine_desc { /* * Note! The first four elements are used * by assembler code in head-armv.S */ unsigned int nr; /* architecture number */ unsigned int phys_io; /* start of physical io */ unsigned int io_pg_offst; /* byte offset for io * page tabe entry */ const char *name; /* architecture name */ unsigned long boot_params; /* tagged list */ unsigned int video_start; /* start of video RAM */ unsigned int video_end; /* end of video RAM */ unsigned int reserve_lp0 :1; /* never has lp0 */ unsigned int reserve_lp1 :1; /* never has lp1 */ unsigned int reserve_lp2 :1; /* never has lp2 */ unsigned int soft_reboot :1; /* soft reboot */ void (*fixup)(struct machine_desc *, struct tag *, char **, struct meminfo *); void (*map_io)(void);/* IO mapping function */ void (*init_irq)(void); struct sys_timer *timer; /* system tick timer */ void (*init_machine)(void); };
我们打开arch.h文件，看到对machine_desc结构体的定义确实和我们刚刚所说的一样。再回到head-common.S文件，这里对mmap_switch定义：
.type __mmap_switched, %function __mmap_switched: adr r3, __switch_data + 4 ldmia r3!, {r4, r5, r6, r7} cmp r4, r5 @ Copy data segment if needed 1: cmpne r5, r6 ldrne fp, [r4], #4 strne fp, [r5], #4 bne 1b mov fp, #0 @ Clear BSS (and zero fp) 1: cmp r6, r7 strcc fp, [r6],#4 bcc 1b ldmia r3, {r4, r5, r6, sp} str r9, [r4] @ Save processor ID str r1, [r5] @ Save machine type bic r4, r0, #CR_A @ Clear 'A' bit stmia r6, {r0, r4} @ Save control register values b start_kernel