第 1 章 引导过程与内核初始化

sys/i386/i386/machdep.c:
		kern_envp = (caddr_t)bootinfo.bi_envp + KERNBASE;

	/* 初始化基本可调整项,如hz等 */
	init_param1();

sys/kern/subr_param.c
	hz = HZ;
	TUNABLE_INT_FETCH("kern.hz", hz);

/usr/src/sys/sys/kernel.h
#define	TUNABLE_INT_FETCH(path, var)	getenv_int((path), (var))

sys/i386/i386/machdep.c:
union descriptor gdt[NGDT * MAXCPU];	/* 全局描述符表 */

sys/i386/include/segments.h:
/*
 * 全局描述符表(GDT)中的入口
 */
#define	GNULL_SEL	0	/* 空描述符 */
#define	GCODE_SEL	1	/* 内核代码描述符 */
#define	GDATA_SEL	2	/* 内核数据描述符 */
#define	GPRIV_SEL	3	/* 对称多处理(SMP)每处理器专有数据 */
#define	GPROC0_SEL	4	/* Task state process slot zero and up, 任务状态进程 */
#define	GLDT_SEL	5	/* 每个进程的局部描述符表 */
#define	GUSERLDT_SEL	6	/* 用户自定义的局部描述符表 */
#define	GTGATE_SEL	7	/* 进程任务切换关口 */
#define	GBIOSLOWMEM_SEL	8	/* BIOS低端内存访问(必须是这第8个入口) */
#define	GPANIC_SEL	9	/* 会导致全系统异常中止工作的任务状态 */
#define GBIOSCODE32_SEL	10	/* BIOS接口(32位代码) */
#define GBIOSCODE16_SEL	11	/* BIOS接口(16位代码) */
#define GBIOSDATA_SEL	12	/* BIOS接口(数据) */
#define GBIOSUTIL_SEL	13	/* BIOS接口(工具) */
#define GBIOSARGS_SEL	14	/* BIOS接口(自变量，参数) */

sys/i386/i386/machdep.c:
static struct gate_descriptor idt0[NIDT];
struct gate_descriptor *idt = idt0[0];	/* 中断描述符表 */

sys/i386/i386/machdep.c:
 	setidt(0x80, IDTVEC(int0x80_syscall),
			SDT_SYS386TGT, SEL_UPL, GSEL(GCODE_SEL, SEL_KPL));

sys/i386/i386/machdep.c:
	cninit();
/* 以下代码可能因为未定义宏DDB而被跳过 */
#ifdef DDB
	kdb_init();
	if (boothowto  RB_KDB)
		Debugger("Boot flags requested debugger");
#endif

/usr/include/machine/segments.h
#define	LSYS5CALLS_SEL	0	/* Intel BCS强制要求的 */
#define	LSYS5SIGR_SEL	1
#define	L43BSDCALLS_SEL	2	/* 尚无 */
#define	LUCODE_SEL	3
#define	LSOL26CALLS_SEL	4	/* Solaris =2.6版系统调用关口 */
#define	LUDATA_SEL	5
/* separate stack, es,fs,gs sels ? 分别的栈、es、fs、gs选择符？ */
/* #define	LPOSIXCALLS_SEL	5*/	/* notyet, 尚无 */
#define LBSDICALLS_SEL	16	/* BSDI system call gate, BSDI系统调用关口 */
#define NLDT		(LBSDICALLS_SEL + 1)

sys/kern/kern_init.c:
    struct	proc proc0;

sys/kern/init_main.c:
	for (sipp = sysinit; *sipp; sipp++) {

		/* ... 省略 ... */

		/* 调用函数 */
		(*((*sipp)-func))((*sipp)-udata);
		/* ... 省略 ... */
	}

sys/kern/init_main.c:
static void
print_caddr_t(void *data __unused)
{
	printf("%s", (char *)data);
}
SYSINIT(announce, SI_SUB_COPYRIGHT, SI_ORDER_FIRST, print_caddr_t, copyright)

/usr/include/sys/kernel.h:
      #define C_SYSINIT(uniquifier, subsystem, order, func, ident) \
      static struct sysinit uniquifier ## _sys_init = { \ subsystem, \
      order, \ func, \ ident \ }; \ DATA_SET(sysinit_set,uniquifier ##
      _sys_init);

#define	SYSINIT(uniquifier, subsystem, order, func, ident)	\
	C_SYSINIT(uniquifier, subsystem, order,			\
	(sysinit_cfunc_t)(sysinit_nfunc_t)func, (void *)ident)

/usr/include/linker_set.h
#define MAKE_SET(set, sym)						\
	static void const * const __set_##set##_sym_##sym = sym;	\
	__asm(".section .set." #set ",\"aw\"");				\
	__asm(".long " #sym);						\
	__asm(".previous")
#endif
#define TEXT_SET(set, sym) MAKE_SET(set, sym)
#define DATA_SET(set, sym) MAKE_SET(set, sym)

static struct sysinit announce_sys_init = {
	SI_SUB_COPYRIGHT,
	SI_ORDER_FIRST,
	(sysinit_cfunc_t)(sysinit_nfunc_t)  print_caddr_t,
	(void *) copyright
};

static void const *const __set_sysinit_set_sym_announce_sys_init =
    announce_sys_init;
__asm(".section .set.sysinit_set" ",\"aw\"");
__asm(".long " "announce_sys_init");
__asm(".previous");

sys/kern/init_main.c:
      extern struct linker_set sysinit_set; /* XXX */

/usr/include/linker_set.h:
  struct linker_set {
	int	ls_length;
	void	*ls_items[1];		/* ls_length个项的数组, 以NULL结尾 */
};

/usr/include/sys/kernel.h:
enum sysinit_sub_id {
	SI_SUB_DUMMY		= 0x0000000,	/* 不被执行，仅供链接器使用 */
	SI_SUB_DONE		= 0x0000001,	/* 已被处理*/
	SI_SUB_CONSOLE		= 0x0800000,	/* 控制台*/
	SI_SUB_COPYRIGHT	= 0x0800001,	/* 最早使用控制台的对象 */
...
	SI_SUB_RUN_SCHEDULER	= 0xfffffff	/* 调度器:不返回 */
};

sys/kern/init_main.c:
static void
create_init(const void *udata __unused)
{
	int error;
	int s;

	s = splhigh();
	error = fork1(proc0, RFFDG | RFPROC, initproc);
	if (error)
		panic("cannot fork init: %d\n", error);
	initproc-p_flag |= P_INMEM | P_SYSTEM;
	cpu_set_fork_handler(initproc, start_init, NULL);
	remrunqueue(initproc);
	splx(s);
}
SYSINIT(init,SI_SUB_CREATE_INIT, SI_ORDER_FIRST, create_init, NULL)

sys/kern/init_main.c:
static char init_path[MAXPATHLEN] =
#ifdef	INIT_PATH
    __XSTRING(INIT_PATH);
#else
    "/sbin/init:/sbin/oinit:/sbin/init.bak:/stand/sysinstall";
#endif