linux arch/arm/kernel/head.code分析

uboot调用内核时传递的参数是 r1=Machine_ID  
ENTRY(stext)
setmode PSR_F_BIT | PSR_I_BIT | SVC_MODE, r9 @ ensure svc mode
@ and irqs disabled
mrc p15, 0, r9, c0, c0 @ get processor id
bl __lookup_processor_type @ 返回值r5=procinfo   r9=cpuid  

*    r9 = cpuid
 * Returns:
 *    r3, r4, r6 corrupted
 *    r5 = proc_info pointer in physical address space
 *    r9 = cpuid (preserved)
 */
    __CPUINIT
__lookup_processor_type:
    adr    r3, __lookup_processor_type_data  r3=下面31行代码的物理地址
    ldmia    r3, {r4 - r6}      r4=下面31行的虚拟地址  r5= __proc_info_end  r6=__proc_info_end
     
				
					
						
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						VMLINUX_SYMBOL(__proc_info_begin) = .;      属性段的开始地址          \
    *(.proc.info.init)         此属性的结构体都在这个地址处
  由于在配置文件中自定义了 config_cpu_arm920t =1 所以只会调用proc-arm920这个文件 即此段属性中只会有arm920t的proc结构体    \
    VMLINUX_SYMBOL(__proc_info_end) = .    属性段的结束地址
   
								
									
										
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										.align

    .section ".proc.info.init", #alloc, #execinstr

    .type    __arm920_proc_info,#object
__arm920_proc_info:
    .long    0x41009200
    .long    0xff00fff0
    .long   PMD_TYPE_SECT | \
        PMD_SECT_BUFFERABLE | \
        PMD_SECT_CACHEABLE | \
        PMD_BIT4 | \
        PMD_SECT_AP_WRITE | \
        PMD_SECT_AP_READ
    .long   PMD_TYPE_SECT | \
        PMD_BIT4 | \
        PMD_SECT_AP_WRITE | \
        PMD_SECT_AP_READ
    b    __arm920_setup
    .long    cpu_arch_name
    .long    cpu_elf_name
    .long    HWCAP_SWP | HWCAP_HALF | HWCAP_THUMB
    .long    cpu_arm920_name
    .long    arm920_processor_functions
    .long    v4wbi_tlb_fns
    .long    v4wb_user_fns
#ifndef CONFIG_CPU_DCACHE_WRITETHROUGH
    .long    arm920_cache_fns
#else
    .long    v4wt_cache_fns
#endif
    .size    __arm920_proc_info, . - __arm920_proc_info
// 处理器的信息
    struct proc_info_list {
unsigned int		cpu_val;  //处理器类型
unsigned int		cpu_mask;  //处理器掩码
unsigned long		__cpu_mm_mmu_flags;	/* used by head.S */
unsigned long		__cpu_io_mmu_flags;	/* used by head.S */
unsigned long		__cpu_flush;		/* used by head.S */
const char		*arch_name;
const char		*elf_name;
unsigned int		elf_hwcap;
const char		*cpu_name;
struct processor	*proc;
struct cpu_tlb_fns	*tlb;
struct cpu_user_fns	*user;
struct cpu_cache_fns	*cache;
};
    sub    r3, r3, r4            @ get offset between virt&phy//物理地址-虚拟地址的差值
    add    r5, r5, r3            @ convert virt addresses to //对应_proc_info_begin 的物理地址
    add    r6, r6, r3            @ physical address space   //对应_proc_info_end 的物理地址
1:    ldmia    r5, {r3, r4}            @ //r3=value,r4= mask
    and    r4, r4, r9            @ mask wanted bits
    teq    r3, r4
    beq    2f
    add    r5, r5, #PROC_INFO_SZ        @ sizeof(proc_info_list)
    cmp    r5, r6
    blo    1b
    mov    r5, #0                @ unknown processor
2:    mov    pc, lr
ENDPROC(__lookup_processor_type)

/*
 * Look in <asm/procinfo.h> for information about the __proc_info structure.
 */
    .align    2
    .type    __lookup_processor_type_data, %object
__lookup_processor_type_data:
    .long    .
    .long    __proc_info_begin
    .long    __proc_info_end
    .size    __lookup_processor_type_data, . - __lookup_processor_type_data

movs r10, r5                  @ invalid processor (r5=0)?
 THUMB( it eq )                   @ force fixup-able long branch encoding
beq __error_p                         @ yes, error 'p'
bl __lookup_machine_type           @ r5=machinfo //查找对应的机器id
      

* r1 = machine architecture number
 * Returns:
 * r3, r4, r6 corrupted
 * r5 = mach_info pointer in physical address space
 */
__lookup_machine_type:
    adr    r3, __lookup_machine_type_data  //r3= __lookup_machine_type_data 的物理地址 即下面第29的物理地址
    ldmia    r3, {r4, r5, r6} r4=.long的虚拟地址(下面第29行的地址) r5=_arch_info_begin的虚拟地址 r6=arch_info_end的地址
                              
				
					
						
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						__arch_info_begin = .;  arch属性段的开始地址
            *(.arch.info.init) arch_info的结构体  会根据CONFIG_MACH_FENG2440 CONFIG_MACH_SMDK2440是否被定义
                                  来确定内核将支持那个board  通过make menuconfig 方式来选择变量 定义情况 分析Kconfig文件可知
__arch_info_end = .；   arch属性段的结束地址
   
								
									
										
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										struct machine_desc {
    unsigned int        nr;        /* architecture number    */
    const char        *name;        /* architecture name    */
    unsigned long        boot_params;    /* tagged list        */

    unsigned int        nr_irqs;    /* number of IRQs */

    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            (*reserve)(void);/* reserve mem blocks    */
    void            (*map_io)(void);/* IO mapping function    */
    void            (*init_early)(void);
    void            (*init_irq)(void);
    struct sys_timer    *timer;        /* system tick timer    */
    void            (*init_machine)(void);
#ifdef CONFIG_MULTI_IRQ_HANDLER
    void            (*handle_irq)(struct pt_regs *);
#endif
};
 machine宏定义如下
 #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      };
										
											
											
												  以smdk2440为例
MACHINE_START(S3C2440, "SMDK2440")
.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

宏展开后得到
static const struct machine_desc   __mach_desc_S3C2440       __used	__attribute__((__section__(".arch.info.init")))
= { 
     .nr		= MACH_TYPE_S3C2440,		\
     .name		= SMDK2440,
     .init_irq	= s3c24xx_init_irq,
     .map_io	 = smdk2440_map_io,
    .init_machine	= smdk2440_machine_init,
    .timer	 = &s3c24xx_timer,

     };
board的结构体
    sub    r3, r3, r4            @ get offset between virt&phys
    add    r5, r5, r3            @ convert virt addresses to
    add    r6, r6, r3            @ physical address space
1:    ldr    r3, [r5, #MACHINFO_TYPE]    @ get machine type
    teq    r3, r1                @ matches loader number?
    beq    2f                @ found
    add    r5, r5, #SIZEOF_MACHINE_DESC    @ next machine_desc
    cmp    r5, r6
    blo    1b
    mov    r5, #0                @ unknown machine
2:    mov    pc, lr
ENDPROC(__lookup_machine_type)

/*
 * Look in arch/arm/kernel/arch.[ch] for information about the
 * __arch_info structures.
 */
    .align    2
    .type    __lookup_machine_type_data, %object
__lookup_machine_type_data:
    .long    .
    .long    __arch_info_begin
    .long    __arch_info_end
    .size    __lookup_machine_type_data, . - __lookup_machine_type_data

movs r8, r5 @ invalid machine (r5=0)?
 THUMB( it eq ) @ force fixup-able long branch encoding
beq __error_a @ yes, error 'a'

/*
* r1 = machine no, r2 = atags,
* r8 = machinfo, r9 = cpuid, r10 = procinfo
*/
bl __vet_atags
#ifdef CONFIG_SMP_ON_UP
bl __fixup_smp
#endif
bl __create_page_tables // 创建页表

ldr r13, =__mmap_switched @ address to jump to after @ mmu has been enabled
// 复制数据 清bss段 保存processor_id=cpu id  保存_machine_arch_typ=machine id   调用start_kernel
adr lr, BSYM(1f) @ return (PIC) address
 ARM( add pc, r10, #PROCINFO_INITFUNC )
 THUMB( add r12, r10, #PROCINFO_INITFUNC )
 THUMB( mov pc, r12 )
1: b __enable_mmu
ENDPROC(stext)
.ltorg