.section ".text.head", "ax".type    stext, %function
ENTRY(stext)msr    cpsr_c, #PSR_F_BIT | PSR_I_BIT | SVC_MODE @ ensure svc mode@ and irqs disabledmrc    p15, 0, r9, c0, c0        @ get processor idbl    __lookup_processor_type        @ r5=procinfo r9=cpuidmovs    r10, r5                @ invalid processor (r5=0)?beq    __error_p            @ yes, error 'p'bl    __lookup_machine_type        @ r5=machinfomovs    r8, r5                @ invalid machine (r5=0)?beq    __error_a            @ yes, error 'a'bl    __create_page_tablesldr    r13, __switch_data        @ address to jump to after@ mmu has been enabledadr    lr, __enable_mmu        @ return (PIC) addressadd    pc, r10, #PROCINFO_INITFUNC

    .type    __lookup_machine_type, %function
__lookup_machine_type:adr    r3, 3bldmia    r3, {r4, r5, r6}sub    r3, r3, r4            @ get offset between virt&physadd    r5, r5, r3            @ convert virt addresses toadd    r6, r6, r3            @ physical address space
1:    ldr    r3, [r5, #MACHINFO_TYPE]    @ get machine typeteq    r3, r1                @ matches loader number?beq    2f                @ foundadd    r5, r5, #SIZEOF_MACHINE_DESC    @ next machine_desccmp    r5, r6blo    1bmov    r5, #0                @ unknown machine
2:    mov    pc, lr3:    .long    ..long    __arch_info_begin.long    __arch_info_end

SECTIONS
{. = (0xc0000000) + 0x00008000;.text.head : {_stext = .;_sinittext = .;*(.text.head)}.init : { /* Init code and data        */*(.init.text)_einittext = .;__proc_info_begin = .;*(.proc.info.init)__proc_info_end = .;__arch_info_begin = .;*(.arch.info.init)__arch_info_end = .;

Direction:include/asm-arm/arch.h
#define MACHINE_START(_type,_name)            \
static const struct machine_desc __mach_desc_##_type    \__used                            \__attribute__((__section__(".arch.info.init"))) = {    \           .nr        = MACH_TYPE_##_type,        \.name        = _name,#define MACHINE_END                \
};
Direction:arch/arm/mach-s3c2440
MACHINE_START(S3C2440, "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,.init_irq    = s3c24xx_init_irq,.map_io        = smdk2440_map_io,.init_machine    = smdk2440_machine_init,.timer        = &s3c24xx_timer,
MACHINE_END

#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,
};

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);
};

    .type    __mmap_switched, %function
__mmap_switched:adr    r3, __switch_data + 4ldmia    r3!, {r4, r5, r6, r7}cmp    r4, r5                @ Copy data segment if needed
1:    cmpne    r5, r6ldrne    fp, [r4], #4strne    fp, [r5], #4bne    1bmov    fp, #0                @ Clear BSS (and zero fp)
1:    cmp    r6, r7strcc    fp, [r6],#4bcc    1bldmia    r3, {r4, r5, r6, sp}str    r9, [r4]            @ Save processor IDstr    r1, [r5]            @ Save machine typebic    r4, r0, #CR_A            @ Clear 'A' bitstmia    r6, {r0, r4}            @ Save control register valuesb    start_kernel

asmlinkage void __init start_kernel(void){local_irq_disable();early_boot_irqs_off();early_init_irq_lock_class();/** Interrupts are still disabled. Do necessary setups, then* enable them*/lock_kernel();tick_init();boot_cpu_init();page_address_init();printk(KERN_NOTICE);printk(linux_banner);setup_arch(&command_line);setup_command_line(command_line);printk(KERN_NOTICE "Kernel command line: %s\n", boot_command_line);parse_early_param();parse_args("Booting kernel", static_command_line, __start___param,__stop___param - __start___param,&unknown_bootoption);init_IRQ();profile_init();if (!irqs_disabled())printk("start_kernel(): bug: interrupts were enabled early\n");early_boot_irqs_on();local_irq_enable();console_init();rest_init();
}

start_kernelsetup_arch(&command_line);setup_command_line(command_line);unknown_bootoptionobsolete_checksetup    parse_early_paramdo_early_param        rest_init;kernel_initprepare_namespacemount_rootinit_post

bootcmd=nand read.jffs2 0x30007FC0 kernel; bootm 0x30007FC0
bootargs=noinitrd root=/dev/mtdblock3 init=/linuxrc console=ttySAC0

static int __init root_dev_setup(char *line)
{strlcpy(saved_root_name, line, sizeof(saved_root_name));return 1;
}__setup("root=", root_dev_setup);   //传入一个字符串，一个函数

Dir:init.h
#define __setup(str, fn)                    \__setup_param(str, fn, fn, 0)#define __setup_param(str, unique_id, fn, early)            \static char __setup_str_##unique_id[] __initdata = str;    \static struct obs_kernel_param __setup_##unique_id    \__attribute_used__                \__attribute__((__section__(".init.setup")))    \__attribute__((aligned((sizeof(long)))))    \= { __setup_str_##unique_id, fn, early }

Creating 4 MTD partitions on "NAND 256MiB 3,3V 8-bit":
0x00000000-0x00040000 : "bootloader"
0x00040000-0x00060000 : "params"
0x00060000-0x00260000 : "kernel"
0x00260000-0x10000000 : "root"

static struct mtd_partition smdk_default_nand_part[] = {[0] = {.name   = "bootloader",.size   = 0x00040000,.offset    = 0,},[1] = {.name   = "params",.offset = MTDPART_OFS_APPEND,.size   = 0x00020000,},[2] = {.name   = "kernel",.offset = MTDPART_OFS_APPEND,.size   = 0x00200000,},[3] = {.name   = "root",.offset = MTDPART_OFS_APPEND,.size   = MTDPART_SIZ_FULL,}
};