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Diffstat (limited to 'arch/i386/kernel/trampoline.S')
-rw-r--r--arch/i386/kernel/trampoline.S80
1 files changed, 80 insertions, 0 deletions
diff --git a/arch/i386/kernel/trampoline.S b/arch/i386/kernel/trampoline.S
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index 000000000000..fcce0e61b0e7
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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 * In fact we don't actually need a stack so we don't
15 * set one up.
16 *
17 * We jump into the boot/compressed/head.S code. So you'd
18 * better be running a compressed kernel image or you
19 * won't get very far.
20 *
21 * On entry to trampoline_data, the processor is in real mode
22 * with 16-bit addressing and 16-bit data. CS has some value
23 * and IP is zero. Thus, data addresses need to be absolute
24 * (no relocation) and are taken with regard to r_base.
25 *
26 * If you work on this file, check the object module with
27 * objdump --reloc to make sure there are no relocation
28 * entries except for:
29 *
30 * TYPE VALUE
31 * R_386_32 startup_32_smp
32 * R_386_32 boot_gdt_table
33 */
34
35#include <linux/linkage.h>
36#include <asm/segment.h>
37#include <asm/page.h>
38
39.data
40
41.code16
42
43ENTRY(trampoline_data)
44r_base = .
45 wbinvd # Needed for NUMA-Q should be harmless for others
46 mov %cs, %ax # Code and data in the same place
47 mov %ax, %ds
48
49 cli # We should be safe anyway
50
51 movl $0xA5A5A5A5, trampoline_data - r_base
52 # write marker for master knows we're running
53
54 /* GDT tables in non default location kernel can be beyond 16MB and
55 * lgdt will not be able to load the address as in real mode default
56 * operand size is 16bit. Use lgdtl instead to force operand size
57 * to 32 bit.
58 */
59
60 lidtl boot_idt - r_base # load idt with 0, 0
61 lgdtl boot_gdt - r_base # load gdt with whatever is appropriate
62
63 xor %ax, %ax
64 inc %ax # protected mode (PE) bit
65 lmsw %ax # into protected mode
66 # flush prefetch and jump to startup_32_smp in arch/i386/kernel/head.S
67 ljmpl $__BOOT_CS, $(startup_32_smp-__PAGE_OFFSET)
68
69 # These need to be in the same 64K segment as the above;
70 # hence we don't use the boot_gdt_descr defined in head.S
71boot_gdt:
72 .word __BOOT_DS + 7 # gdt limit
73 .long boot_gdt_table-__PAGE_OFFSET # gdt base
74
75boot_idt:
76 .word 0 # idt limit = 0
77 .long 0 # idt base = 0L
78
79.globl trampoline_end
80trampoline_end: