kernel/reboot.c文件是重新启动过程的与体系结构无关的部分。

arch/x86/kernel/reboot.c和所有其他arch/*/kernel/reboot.c是某些功能的体系结构特定版本，由kernel/reboot.c使用。

例如，在arch/x86/kernel/reboot.c中有machine_real_restart() function(假设我们使用BIOS启动，实际选择在native_machine_emergency_restart)，这是最后调用的内核函数。它要求BIOS做实际重新引导：

69 void __noreturn machine_real_restart(unsigned int type)

73 /*

74 * Write zero to CMOS register number 0x0f, which the BIOS POST

75 * routine will recognize as telling it to do a proper reboot. (Well

76 * that's what this book in front of me says -- it may only apply to

77 * the Phoenix BIOS though, it's not clear). At the same time,

78 * disable NMIs by setting the top bit in the CMOS address register,

79 * as we're about to do peculiar things to the CPU. I'm not sure if

80 * `outb_p' is needed instead of just `outb'. Use it to be on the

81 * safe side. (Yes, CMOS_WRITE does outb_p's. - Paul G.)

82 */

84 CMOS_WRITE(0x00, 0x8f);

96 /* Jump to the identity-mapped low memory code */

97 #ifdef CONFIG_X86_32

98 asm volatile("jmpl *%0" : :

99 "rm" (real_mode_header->machine_real_restart_asm),

100 "a" (type));

53 /**

54 * emergency_restart - reboot the system

55 *

56 * Without shutting down any hardware or taking any locks

57 * reboot the system. This is called when we know we are in

58 * trouble so this is our best effort to reboot. This is

59 * safe to call in interrupt context.

60 */

61 void emergency_restart(void)

62 {

63 kmsg_dump(KMSG_DUMP_EMERG);

64 machine_emergency_restart();

65 }

66 EXPORT_SYMBOL_GPL(emergency_restart);

125 /**

126 * kernel_restart - reboot the system

130 * Shutdown everything and perform a clean reboot.

131 * This is not safe to call in interrupt context.

132 */

133 void kernel_restart(char *cmd)

134 {

135 kernel_restart_prepare(cmd);

...

143 machine_restart(cmd);

144 }

145 EXPORT_SYMBOL_GPL(kernel_restart);

我们可以看到，这个通用函数调用特定achine_restart做一切必要的行动来告诉我们重启硬件架构。在x86的它会做......是的，它会调用restart function pointer from machine_ops：

658 void machine_restart(char *cmd)

659 {

660 machine_ops.restart(cmd);

661 }

X86的restart points to的native_machine_restart再次呼吁__machine_emergency_restart，它将调用相同machine_real_restart。