主要内容---内核工作原理解析
1, 内核的编译步骤
2, Kconfig和Makefile的使用
3, 内核的裁剪---make menuconfig
4, 内核的工作原理:
a, 内核的内部构造
b, 内核的启动步骤
c, 内核中module_init是什么
d, 挂载是什么意思
e, 祖先进程init是如何被启动的
----------------------------------------------------
1, 内核的编译步骤
1, 设置交叉工具链
195 ARCH ?= arm
196 CROSS_COMPILE ?= arm-none-linux-gnueabi-
2, 选择当前的soc---s5pv210
make s5pv210_defconfig
3, make menuconfig --内核裁剪
System Type --->
(0) S3C UART to use for low-level messages
注意: 执行make menuconfig 有可能缺少一个包:ncurse
sudo apt-get install libncurses5-dev
4, make zImage 或者 make zImage
Kconfig和Makefile的使用
Kconfig:arch/arm/Kconfig
menu "Test Support"
config MYTEST
tristate "This is a simple test"
help
you can choose y/n/m to build it
choice
prompt "Fruit Type"
config APPLE
bool "I have a apple"
help
i have a pen
config BANANA
bool "yellow banana"
help
give you
config WATERMELON
bool "big xigua"
help
xixixixxixigu
endchoice
endmenu
uImage=64字节头+zImage
uboot: 启动内核---linux, bsd, vxwork, 但是启动方式不一样
linux: arm, x86, mips等
启动zImage: 因为uboot做了移植, 默认认为zImage就是arm架构的linux内核
64字节头包含了描述内核的信息:mkimage增加64字节信息的工具, mkimage是由uboot提供
手动添加64字节头:
farsight@ubuntu:/tftpboot$ ./mkimage
Usage: ./mkimage -l image
-l ==> list image header information
./mkimage [-x] -A arch -O os -T type -C comp -a addr -e ep -n name -d data_file[:data_file...] image
-A ==> set architecture to 'arch'//设定架构:arm, mips, x86
-O ==> set operating system to 'os'//操作系统类型:linux, bsd, vxwork
-T ==> set image type to 'type'//镜像类型: kernel, ramdisk
-C ==> set compression type 'comp'//压缩类型:gzip2, bzip2, none
-a ==> set load address to 'addr' (hex)//内核被加载到内存的地址(参考值): 0x20008000
-e ==> set entry point to 'ep' (hex)//内核被执行的地址: 0x20008000
-n ==> set image name to 'name'// 描述语句:自定义
-d ==> use image data from 'datafile'//指定增加头部信息的文件---zImage
./mkimage -A arm -O linux -T kernel -C none -a 0x20008000 -e 0x20008000 -n "Linux 3.0.8-jihq" -d zImage uImage
Image Name: Linux 3.0.8-jihq
Created: Tue Dec 20 17:49:19 2016
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 1949140 Bytes = 1903.46 kB = 1.86 MB
Load Address: 0x20008000
Entry Point: 0x20008000
如果要启动uImage
FS210 # set bootcmd tftp 0x40008000 uImage \; bootm 0x40008000
FS210 # save
基本的lds脚本:
OUTPUT_ARCH(arm)
ENTRY(_start)
SECTIONS
SECTIONS
{
. = 0x30008000;
.text : {
start.o (.text)
ledc.o (.text)
* (.text)
}
.rodata : {
* (.rodata)
}
.data : {
* (.data)
}
__bss_start = .;
.bss : {
* (.bss)
}
__bss_end = .;
}
内核的内部构造:
559 all: vmlinux
730 # Build vmlinux
731 # ---------------------------------------------------------------------------
732 # vmlinux is built from the objects selected by $(vmlinux-init) and
733 # $(vmlinux-main). Most are built-in.o files from top-level directories
734 # in the kernel tree, others are specified in arch/$(ARCH)/Makefile.
735 # Ordering when linking is important, and $(vmlinux-init) must be first.
736 #
737 # vmlinux
738 # ^
739 # |
740 # +-< $(vmlinux-init)
741 # | +--< init/version.o + more
742 # |
743 # +--< $(vmlinux-main)
744 # | +--< driver/built-in.o mm/built-in.o + more
745 # |
746 # +-< kallsyms.o (see description in CONFIG_KALLSYMS section)
757 vmlinux-init := $(head-y) $(init-y)
758 vmlinux-main := $(core-y) $(libs-y) $(drivers-y) $(net-y)
759 vmlinux-all := $(vmlinux-init) $(vmlinux-main)
760 vmlinux-lds := arch/arm/kernel/vmlinux.lds
arch/arm/kernel/vmlinux.lds:
OUTPUT_ARCH(arm)
ENTRY(stext)
SECTIONS
{
. = 0x80000000 + 0x00008000;
.init : { /* Init code and data */
_stext = .;
_sinittext = .;
*(.head.text)
*(.init.text)
*(.cpuinit.text)
*(.meminit.text)
_einittext = .;
__proc_info_begin = .;
*(.proc.info.init) // 处理器信息段
__proc_info_end = .;
__arch_info_begin = .;
*(.arch.info.init) // 对象对象段,机器信息段--MACHINE_START
__arch_info_end = .;
__tagtable_begin = .;
*(.taglist.init) //uboot传递bootargs数据的处理段
__tagtable_end = .;
__setup_start = .;
*(.init.setup) // bootargs中各个参数的处理段
__setup_end = .;
__initcall_start = .;
*(.initcallearly.init)
__early_initcall_end = .;//驱动函数执行段
*(.initcall0.init) *(.initcall0s.init)
*(.initcall1.init) *(.initcall1s.init)
*(.initcall2.init) *(.initcall2s.init) //这个段全部都是函数指针
*(.initcall3.init) *(.initcall3s.init) //如果批量执行这里的所有函数指针,驱动的入口函数就会被执行
*(.initcall4.init) *(.initcall4s.init) //subsys_initcall
*(.initcall5.init) *(.initcall5s.init)
*(.initcallrootfs.init)
*(.initcall6.init) *(.initcall6s.init) // module_init
*(.initcall7.init) *(.initcall7s.init)
__initcall_end = .;
module_init(led_drv_init); //是一个函数指针,指针指向参数
typedef int (*initcall_t)(void);
#define module_init(x) __initcall(x);
#define __initcall(fn) device_initcall(fn)
#define device_initcall(fn) __define_initcall("6",fn,6)
#define __define_initcall(level,fn,id) \
static initcall_t __initcall_##fn##id __used \
__attribute__((__section__(".initcall" level ".init"))) = fn
module_init(led_drv_init);
==>
static initcall_t __initcall_led_drv_init6
__used __attribute__((__section__(".initcall6.init"))) = led_drv_init
#define pure_initcall(fn) __define_initcall("0",fn,0)
#define core_initcall(fn) __define_initcall("1",fn,1)
#define core_initcall_sync(fn) __define_initcall("1s",fn,1s)
#define postcore_initcall(fn) __define_initcall("2",fn,2)
#define postcore_initcall_sync(fn) __define_initcall("2s",fn,2s)
#define arch_initcall(fn) __define_initcall("3",fn,3)
#define arch_initcall_sync(fn) __define_initcall("3s",fn,3s)
#define subsys_initcall(fn) __define_initcall("4",fn,4)
#define subsys_initcall_sync(fn) __define_initcall("4s",fn,4s)
#define fs_initcall(fn) __define_initcall("5",fn,5)
#define fs_initcall_sync(fn) __define_initcall("5s",fn,5s)
#define rootfs_initcall(fn) __define_initcall("rootfs",fn,rootfs)
#define device_initcall(fn) __define_initcall("6",fn,6)
#define device_initcall_sync(fn) __define_initcall("6s",fn,6s)
#define late_initcall(fn) __define_initcall("7",fn,7)
#define late_initcall_sync(fn) __define_initcall("7s",fn,7s)
MACHINE_START(SMDKV210, "SMDKV210")
/* Maintainer: Kukjin Kim <[email protected]> */
.boot_params = S5P_PA_SDRAM + 0x100,
.init_irq = s5pv210_init_irq,
.map_io = smdkv210_map_io,
.init_machine = smdkv210_machine_init,
.timer = &s5p_timer,
MACHINE_END
#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 \
};
MACHINE_START(SMDKV210, "SMDKV210")
==>
static const struct machine_desc __mach_desc_SMDKV210
__attribute__((__section__(".arch.info.init"))) = {
.nr = MACH_TYPE_SMDKV210, // 2456
.name = "SMDKV210",
.boot_params = S5P_PA_SDRAM + 0x100,// 0x20000100
.init_irq = s5pv210_init_irq,
.map_io = smdkv210_map_io,
.init_machine = smdkv210_machine_init,
.timer = &s5p_timer,
};
farsight@ubuntu:~/linux_system/kernel/linux-3.0.8$ grep -rHn 'MACH_TYPE_SMDKV210' ./include/
./include/generated/mach-types.h:417:#define MACH_TYPE_SMDKV210 2456
static int __init init_setup(char *str)
{
unsigned int i;
execute_command = str;
/*
* In case LILO is going to boot us with default command line,
* it prepends "auto" before the whole cmdline which makes
* the shell think it should execute a script with such name.
* So we ignore all arguments entered _before_ init=... [MJ]
*/
for (i = 1; i < MAX_INIT_ARGS; i++)
argv_init[i] = NULL;
return 1;
}
__setup("init=", init_setup);
#define __setup(str, fn) \
__setup_param(str, fn, fn, 0)
#define __setup_param(str, unique_id, fn, early) \
static const char __setup_str_##unique_id[] __initconst \
__aligned(1) = str; \
static struct obs_kernel_param __setup_##unique_id \
__used __section(.init.setup) \
__attribute__((aligned((sizeof(long))))) \
= { __setup_str_##unique_id, fn, early }
==>
static const char __setup_str_init_setup[] __section(.init.rodata) = "init=";
__setup("init=", init_setup);
static struct obs_kernel_param
__setup_init_setup
__used __section(.init.setup)
= {
"init=" //__setup_str_init_setup,
init_setup,
0
};
struct obs_kernel_param {
const char *str;
int (*setup_func)(char *);
int early;
};
启动流程:
第一个阶段: arch/arm/kernel/head.S
__HEAD
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 @ r5=procinfo r9=cpuid
bl __create_page_tables
ldr r13, =__mmap_switched @ address to jump to after
@ mmu has been enabled
adr lr, BSYM(1f) @ return (PIC) address
mov r8, r4 @ set TTBR1 to swapper_pg_dir
ARM( add pc, r10, #PROCINFO_INITFUNC )
THUMB( add r12, r10, #PROCINFO_INITFUNC )
THUMB( mov pc, r12 )
1: b __enable_mmu
__mmap_switched:// head-common.S
adr r3, __mmap_switched_data
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
ARM( ldmia r3, {r4, r5, r6, r7, sp})
THUMB( ldmia r3, {r4, r5, r6, r7} )
THUMB( ldr sp, [r3, #16] )
str r9, [r4] @ Save processor ID
str r1, [r5] @ Save machine type
str r2, [r6] @ Save atags pointer
bic r4, r0, #CR_A @ Clear 'A' bit
stmia r7, {r0, r4} @ Save control register values
b start_kernel
init/main.c
asmlinkage void __init start_kernel(void)
|
printk(KERN_NOTICE "%s", linux_banner);
setup_arch(&command_line);//初始化cpu和机器的代码,找到机器描述对象
|//通过2456,找到对应的struct machine_desc
|//从0x20000100中去获取到了uboot传递过来的参数
struct machine_desc *mdesc;
mdesc = setup_machine_tags(machine_arch_type);//machine_arch_type=2456
|
struct machine_desc *mdesc = NULL, *p;
for (p = __arch_info_begin; p < __arch_info_end; p++)
if (nr == p->nr) {// 比对2456
printk("Machine: %s\n", p->name);
mdesc = p;
return mdesc;
machine_desc = mdesc;//将遍历到的machine_desc赋值给machine_desc
printk(KERN_NOTICE "Kernel command line: %s\n", boot_command_line);
parse_early_param();
//分析bootargs中的所有参数
//console=ttySAC0,115200 root=/dev/nfs nfsroot=192.168.7.3:/opt/rootfs ip=192.168.7.7 init=/linuxrc
parse_args("Booting kernel", static_command_line, __start___param,
__stop___param - __start___param,
&unknown_bootoption);
//有一个应用: 在bootargs中可以自定义传递参数
// set bootargs myname=ruhua myage=250
/*
内核中需要拿到ruhua和250
就必须在任何一个文件中添加如下内容:
init/main.c
static int __init myname_setup(char *str)
{
printk("---------> name = %s\n", str);
return 1;
}
__setup("myname=", myname_setup);
static int __init myage_setup(char *str)
{
int age = simple_strtoul(str, NULL, 10);
printk("--------->age = %d\n", age/10);
return 1;
}
__setup("myage=", myage_setup);
*/
rest_init();
|
kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
|
do_basic_setup();//执行所有驱动的入口函数
|
do_initcalls();
|
initcall_t *fn;
for (fn = __early_initcall_end; fn < __initcall_end; fn++)
do_one_initcall(*fn);
|
ret = fn();//批量的执行了initcallX.init段中所有函数指针
//也就执行了所有驱动的入口函数
prepare_namespace();//挂载根文件系统
init_post();//执行祖先init进程
|
if (execute_command) {// init=/linuxrc, execute_command="/linuxrc"
//优先执行bootage中指定的祖先进程
run_init_process(execute_command);
printk(KERN_WARNING "Failed to execute %s. Attempting "
"defaults...\n", execute_command);
}
//如果没有执行,就执行备胎
run_init_process("/sbin/init");
run_init_process("/etc/init");
run_init_process("/bin/init");
run_init_process("/bin/sh");
panic("No init found. Try passing init= option to kernel. "
"See Linux Documentation/init.txt for guidance.");
pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
|
create_kthread(create);//创建其他线程
schedule();//让出调度权
do_basic_setup();
|
do_initcalls();
|
initcall_t *fn;
for (fn = __early_initcall_end; fn < __initcall_end; fn++)
do_one_initcall(*fn);
|
ret = fn();//批量的执行了initcallX.init段中所有函数指针
//也就执行了所有驱动的入口函数
farsight@ubuntu:~/linux_system/kernel/linux-3.0.8$ grep -rHn '>init_machine' ./arch/arm/
./arch/arm/kernel/setup.c:732: if (machine_desc->init_machine)
./arch/arm/kernel/setup.c:733: machine_desc->init_machine();
