1/*
2 *
3 *	Trampoline.S	Derived from Setup.S by Linus Torvalds
4 *
5 *	4 Jan 1997 Michael Chastain: changed to gnu as.
6 *
7 *	Entry: CS:IP point to the start of our code, we are
8 *	in real mode with no stack, but the rest of the
9 *	trampoline page to make our stack and everything else
10 *	is a mystery.
11 *
12 *	In fact we don't actually need a stack so we don't
13 *	set one up.
14 *
15 *	On entry to trampoline_data, the processor is in real mode
16 *	with 16-bit addressing and 16-bit data.  CS has some value
17 *	and IP is zero.  Thus, data addresses need to be absolute
18 *	(no relocation) and are taken with regard to r_base.
19 *
20 *	If you work on this file, check the object module with objdump
21 *	--full-contents --reloc to make sure there are no relocation
22 *	entries. For the GDT entry we do hand relocation in smpboot.c
23 *	because of 64bit linker limitations.
24 */
25
26#include <linux/linkage.h>
27#include <asm/segment.h>
28#include <asm/page.h>
29
30.data
31
32.code16
33
34ENTRY(trampoline_data)
35r_base = .
36
37	mov	%cs, %ax	# Code and data in the same place
38	mov	%ax, %ds
39
40	mov	$1, %bx		# Flag an SMP trampoline
41	cli			# We should be safe anyway
42
43	movl	$0xA5A5A5A5, trampoline_data - r_base
44				# write marker for master knows we're running
45
46	lidt	idt_48 - r_base	# load idt with 0, 0
47	lgdt	gdt_48 - r_base	# load gdt with whatever is appropriate
48
49	movw    $__KERNEL_DS,%ax
50	movw    %ax,%ds
51	movw    %ax,%es
52
53	xor	%ax, %ax
54	inc	%ax		# protected mode (PE) bit
55	lmsw	%ax		# into protected mode
56	jmp	flush_instr
57flush_instr:
58	ljmpl	$__KERNEL32_CS, $0x00100000
59			# jump to startup_32 in arch/x86_64/kernel/head.S
60
61idt_48:
62	.word	0			# idt limit = 0
63	.word	0, 0			# idt base = 0L
64
65gdt_48:
66	.short	0x0800			# gdt limit = 2048, 256 GDT entries
67	.globl tramp_gdt_ptr
68tramp_gdt_ptr:
69	.long	0			# gdt base = gdt (first SMP CPU)
70					# this is filled in by C because the 64bit
71					# linker doesn't support absolute 32bit
72					# relocations.
73
74
75.globl trampoline_end
76trampoline_end:
77