参考资料：https://www.bilibili.com/video/BV12E411h71h?p=38&vd_source=432ba293ecfc949a4174ab91ccc526d6 Linux内核链接脚本arch/arm/kernel/vmlinux.lds arch/arm/kernel/vmlinux.lds中
OUTPUT_ARCH(arm)
ENTRY(stext) // Linux内核入口，入口函数stext
jiffies = jiffies_64;
SECTIONS
{
/*
* XXX: The linker does not define how output sections are
* assigned to input sections when there are multiple statements
* matching the same input section name. There is no documented
* order of matching.
*
* unwind exit sections must be discarded before the rest of the
* unwind sections get included.
*/
/DISCARD/ : {
*(.ARM.exidx.exit.text)
*(.ARM.extab.exit.text)
... ...
arch/arm/kernel/head.S
/*
* Kernel startup entry point.
* ---------------------------
*
* This is normally called from the decompressor code. The requirements
* are: MMU = off, D-cache = off, I-cache = dont care, r0 = 0,
* r1 = machine nr, r2 = atags or dtb pointer.
*
* This code is mostly position independent, so if you link the kernel at
* 0xc0008000, you call this at __pa(0xc0008000).
*
* See linux/arch/arm/tools/mach-types for the complete list of machine
* numbers for r1.
*
* We're trying to keep crap to a minimum; DO NOT add any machine specific
* crap here - that's what the boot loader (or in extreme, well justified
* circumstances, zImage) is for.
*/
ENTRY(stext)
ARM_BE8(setend be ) @ ensure we are in BE8 mode
THUMB( adr r9, BSYM(1f) ) @ Kernel is always entered in ARM.
THUMB( bx r9 ) @ If this is a Thumb-2 kernel,
THUMB( .thumb ) @ switch to Thumb now.
THUMB(1: )
#ifdef CONFIG_ARM_VIRT_EXT
bl __hyp_stub_install
#endif
@ ensure svc mode and all interrupts masked
safe_svcmode_maskall r9 // 确保CPU处于svc模式，并且关闭了所有的中断
mrc p15, 0, r9, c0, c0 @ get processor id
bl __lookup_processor_type @ r5=procinfo r9=cpuid // 检查当前系统是否支持此CPU，如果支持就获取procinfo信息
movs r10, r5 @ invalid processor (r5=0)?
THUMB( it eq ) @ force fixup-able long branch encoding
beq __error_p @ yes, error 'p'
... ...
/*
* r1 = machine no, r2 = atags or dtb,
* r8 = phys_offset, r9 = cpuid, r10 = procinfo
*/
bl __vet_atags
#ifdef CONFIG_SMP_ON_UP
bl __fixup_smp
#endif
#ifdef CONFIG_ARM_PATCH_PHYS_VIRT
bl __fixup_pv_table
#endif
bl __create_page_tables // 创建页表
/*
* The following calls CPU specific code in a position independent
* manner. See arch/arm/mm/proc-*.S for details. r10 = base of
* xxx_proc_info structure selected by __lookup_processor_type
* above. On return, the CPU will be ready for the MMU to be
* turned on, and r0 will hold the CPU control register value.
*/
ldr r13, =__mmap_switched @ address to jump to after // r13保存着__mmap_switched函数的地址
@ mmu has been enabled
adr lr, BSYM(1f) @ return (PIC) address
mov r8, r4 @ set TTBR1 to swapper_pg_dir
ldr r12, [r10, #PROCINFO_INITFUNC]
add r12, r12, r10
ret r12
1: b __enable_mmu // 使能MMU
ENDPROC(stext)
image和zImage都是经过压缩的，Linux内核会先进行解压缩，解压缩完成以后就要运行Linux内核，要求：
1、MMU关闭
2、D cache关闭
3、I cache无所谓
4、r0 = 0，uboot中kernel_entry函数传递来的
5、r1 = machine id，在使用设备树的内核没有用到，uboot中kernel_entry函数传递来的
6、r2 设备树首地址，uboot中kernel_entry函数传递来的
arch/arm/kernel/head-common.S
... ...
__mmap_switched:
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
cmp r7, #0
strne r0, [r7] @ Save control register values
b start_kernel // 启动linux内核，该函数在init/main.c中
ENDPROC(__mmap_switched)
... ...
init/main.c
asmlinkage __visible void __init start_kernel(void) // 用于声明函数调用约定的宏，它告诉编译器不要对函数参数进行寄存器优化
{
char *command_line;
char *after_dashes;
lockdep_init(); // lockstep是死锁检查模块
set_task_stack_end_magic(&init_task);
smp_setup_processor_id(); // 跟SMP相关
debug_objects_early_init(); // 做一些和debug相关的初始化
/*
* Set up the the initial canary ASAP:
*/
boot_init_stack_canary(); // 栈溢出检测初始化
cgroup_init_early();
local_irq_disable(); // 关闭当前CPU中断
early_boot_irqs_disabled = true;
/*
* Interrupts are still disabled. Do necessary setups, then
* enable them
*/
boot_cpu_init(); // 跟 CPU 有关的初始化
page_address_init(); // 页地址相关的初始化
pr_notice("%s", linux_banner);
setup_arch(&command_line);
mm_init_cpumask(&init_mm);
setup_command_line(command_line);
setup_nr_cpu_ids();
setup_per_cpu_areas(); // 在 SMP 系统中有用，设置每个 CPU 的 per-cpu 数据
smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
build_all_zonelists(NULL, NULL);
page_alloc_init();
pr_notice("Kernel command line: %s\n", boot_command_line);
parse_early_param();
after_dashes = parse_args("Booting kernel",
static_command_line, __start___param,
__stop___param - __start___param,
-1, -1, &unknown_bootoption);
if (!IS_ERR_OR_NULL(after_dashes))
parse_args("Setting init args", after_dashes, NULL, 0, -1, -1,
set_init_arg);
jump_label_init();
... ...
thread_info_cache_init();
cred_init();
fork_init();
proc_caches_init(); // 给各种资源管理结构分配缓存
buffer_init(); // 初始化缓冲缓存
key_init();
security_init();
dbg_late_init();
vfs_caches_init(totalram_pages);
signals_init();
/* rootfs populating might need page-writeback */
page_writeback_init();
proc_root_init(); // 注册并挂载 proc 文件系统
nsfs_init();
cpuset_init();
cgroup_init();
taskstats_init_early();
delayacct_init();
check_bugs();
acpi_subsystem_init();
sfi_init_late();
if (efi_enabled(EFI_RUNTIME_SERVICES)) {
efi_late_init();
efi_free_boot_services();
}
ftrace_init();
/* Do the rest non-__init'ed, we're now alive */
rest_init(); // rest_init 函数
}
arch/init.c
... ...
static noinline void __init_refok rest_init(void)
{
int pid;
rcu_scheduler_starting(); // 启动 RCU 锁调度器
smpboot_thread_init();
/*
* We need to spawn init first so that it obtains pid 1, however
* the init task will end up wanting to create kthreads, which, if
* we schedule it before we create kthreadd, will OOPS.
*/
// 创建kernel_init进程，init进程也就是PID为1的进程，init进程一开始是内核进程，后面Init进程会在根文件系统中查看名为"init" 这个程序，这个"init"程序处于用户态
// 通过运行这个"init"程序，Init进程就会实现从内核态到用户态的转变
kernel_thread(kernel_init, NULL, CLONE_FS);
numa_default_policy();
pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES); // PID为2的进程
rcu_read_lock();
kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
rcu_read_unlock();
complete(&kthreadd_done);
/*
* The boot idle thread must execute schedule()
* at least once to get things moving:
*/
init_idle_bootup_task(current);
schedule_preempt_disabled();
/* Call into cpu_idle with preempt disabled */
// 进入 idle 进程，cpu_startup_entry 会调用cpu_idle_loop，cpu_idle_loop 是个 while 循环，也就是 idle 进程代码，idle进程是由主线程演变而来的
// 调用cpu_idle_loop
cpu_startup_entry(CPUHP_ONLINE);
}
... ...
通过ps -A可查看进程ID
init进程说明：
kernel_init
->kernel_init_freeable
->设置标准输入/标准输出/标准错误使用/dev/console
->ramdisk_execute_command = "/init"
->检查/init是否存在，存在的话就运行
->uboot传递给linux内核的bootargs可以自定义init = xxx，或者叫命令行参数。有些开发板会设置init = linuxrc
->上一步也不存在，试着运行/sbin/init，还没有的话运行/etc/init，/bin/init，bin/init，这也就是linux用户进程的第一个程序，该程序位于根文件系统中
static int __ref kernel_init(void *unused)
{
int ret;
kernel_init_freeable();
/* need to finish all async __init code before freeing the memory */
async_synchronize_full();
free_initmem();
mark_rodata_ro();
system_state = SYSTEM_RUNNING;
numa_default_policy();
flush_delayed_fput();
if (ramdisk_execute_command) {
ret = run_init_process(ramdisk_execute_command);
if (!ret)
return 0;
pr_err("Failed to execute %s (error %d)\n",
ramdisk_execute_command, ret);
}
/*
* We try each of these until one succeeds.
*
* The Bourne shell can be used instead of init if we are
* trying to recover a really broken machine.
*/
if (execute_command) {
ret = run_init_process(execute_command);
if (!ret)
return 0;
panic("Requested init %s failed (error %d).",
execute_command, ret);
}
if (!try_to_run_init_process("/sbin/init") ||
!try_to_run_init_process("/etc/init") ||
!try_to_run_init_process("/bin/init") ||
!try_to_run_init_process("/bin/sh"))
return 0;
panic("No working init found. Try passing init= option to kernel. "
"See Linux Documentation/init.txt for guidance.");
}
static noinline void __init kernel_init_freeable(void) {
... ...
/*
* check if there is an early userspace init. If yes, let it do all
* the work
*/
if (!ramdisk_execute_command)
ramdisk_execute_command = "/init";
if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
ramdisk_execute_command = NULL;
prepare_namespace();
}
... ...
}
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);
标签：__,kernel,execute,...,简介,init,command,内核,Linux
From： https://www.cnblogs.com/lethe1203/p/18089694