linux内核启动解析（三）

1、linux内核启动解析（三） 1.2 _lookup_machine_type() 机器类型的查找代码如下：_lookup_machine_type:adr r3, 3bldmia r3, r4, r5, r6sub r3, r3, r4 get offset between virt&physadd r5, r5, r3 convert virt addresses toadd r6, r6, r3 physical address space1: ldr r3, r5, machinfo_type get machine typeteq r3, r1 matches loader

2、number?beq 2f foundadd r5, r5, sizeof_machine_desc next machine_desccmp r5, r6blo 1bmov r5, 0 unknown machine2: mov pc, lrendproc(_lookup_machine_type)我们可以看到，这和处理器类型查找函数很类似，在这里只举行容易的解说。.long _proc_info_begin.long _proc_info_end3: .long .long _arch_info_begin.long _arch_info_end_arch_info_begin和_arch

3、_info_end在arch/arm/kernel/vlinux.lds.s中定义：_arch_info_begin = .;*(..init)_arch_info_end = .;..init段我们可以找到在arch/arm/include/asm/mach/arch.h中有引用：define machine_start(_type,_name) static const struct machine_desc _mach_desc_type _used _attribute_(_section_("..init")

4、= .nr = mach_type_type, .name = _name,define machine_end ;我们可以在arch/arm/mach-*.c文件中找到一系列关于machine_start所定义的结构。1.3 _vet_atags()函数代码如下：_vet_atags:tst r2, 0x3 aligned?bne 1fldr r5, r2, 0 is first tag atag_core?subs r5, r5, atag_core_sizebne 1fldr r5, r2, 4ldr r6, =atag_corecmp r5, r6bne 1fmov pc, lr at

5、ag pointer is ok1: mov r2, 0mov pc, lrendproc(_vet_atags)atag是bootloader传递给linux内核的参数列表。这个参数列表是以tag的列表形式来表示的。这个列表起始位置的tag是atag_core，用来表示这是一个有效的tag列表。假如起始tag不是atag_core，就认为bootloader没有传递tag参数给内核。以下是tag值的定义和描述，以及tag结构的定义。tag name value size description atag_none 0x00000000 2 empty tag used to end list

6、 atag_core 0x54410001 5 (2 if empty) first tag used to start list atag_mem 0x54410002 4 describes a physical area of memory atag_videotext 0x54410003 5 describes a vga text display atag_ramdisk 0x54410004 5 describes how the ramdisk will be used in kernel atag_initrd2 0x54420005 4 describes where th

7、e compressed ramdisk image is placed in memory atag_serial 0x54410006 4 64 bit board serial number atag_revision 0x54410007 3 32 bit board revision number atag_videolfb 0x54410008 8 initial values for vesafb-type framebuffers atag_cmdline 0x54410009 2 + (length_of_cmdline + 3) / 4) command line to p

8、ass to kernelstruct tag_header _u32 size;_u32 tag;struct tag struct tag_header hdr;union struct tag_core core;struct tag_mem32 mem;struct tag_videotext videotext;struct tag_ramdisk ramdisk;struct tag_initrd initrd;struct tag_serialnr serialnr;struct tag_revision revision;struct tag_videolfb videolfb;struct tag_cmdl