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 *	This is only used for booting secondary CPUs in SMP machine
8 *
9 *	Entry: CS:IP point to the start of our code, we are
10 *	in real mode with no stack, but the rest of the
11 *	trampoline page to make our stack and everything else
12 *	is a mystery.
13 *
14 *	We jump into arch/x86/kernel/head_32.S.
15 *
16 *	On entry to trampoline_data, the processor is in real mode
17 *	with 16-bit addressing and 16-bit data.  CS has some value
18 *	and IP is zero.  Thus, data addresses need to be absolute
19 *	(no relocation) and are taken with regard to r_base.
20 *
21 *	If you work on this file, check the object module with
22 *	objdump --reloc to make sure there are no relocation
23 *	entries except for:
24 *
25 *	TYPE              VALUE
26 *	R_386_32          startup_32_smp
27 *	R_386_32          boot_gdt
28 */
29
30#include <linux/linkage.h>
31#include <linux/init.h>
32#include <asm/segment.h>
33#include <asm/page_types.h>
34
35#ifdef CONFIG_SMP
36
37	.section ".x86_trampoline","a"
38	.balign PAGE_SIZE
39	.code16
40
41ENTRY(trampoline_data)
42r_base = .
43	wbinvd			# Needed for NUMA-Q should be harmless for others
44	mov	%cs, %ax	# Code and data in the same place
45	mov	%ax, %ds
46
47	cli			# We should be safe anyway
48
49	movl	$0xA5A5A5A5, trampoline_status - r_base
50				# write marker for master knows we're running
51
52	/* GDT tables in non default location kernel can be beyond 16MB and
53	 * lgdt will not be able to load the address as in real mode default
54	 * operand size is 16bit. Use lgdtl instead to force operand size
55	 * to 32 bit.
56	 */
57
58	lidtl	boot_idt_descr - r_base	# load idt with 0, 0
59	lgdtl	boot_gdt_descr - r_base	# load gdt with whatever is appropriate
60
61	xor	%ax, %ax
62	inc	%ax		# protected mode (PE) bit
63	lmsw	%ax		# into protected mode
64	# flush prefetch and jump to startup_32_smp in arch/i386/kernel/head.S
65	ljmpl	$__BOOT_CS, $(startup_32_smp-__PAGE_OFFSET)
66
67	# These need to be in the same 64K segment as the above;
68	# hence we don't use the boot_gdt_descr defined in head.S
69boot_gdt_descr:
70	.word	__BOOT_DS + 7			# gdt limit
71	.long	boot_gdt - __PAGE_OFFSET	# gdt base
72
73boot_idt_descr:
74	.word	0				# idt limit = 0
75	.long	0				# idt base = 0L
76
77ENTRY(trampoline_status)
78	.long	0
79
80.globl trampoline_end
81trampoline_end:
82
83#endif /* CONFIG_SMP */
84