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/*
*
* Trampoline.S Derived from Setup.S by Linus Torvalds
*
* 4 Jan 1997 Michael Chastain: changed to gnu as.
*
* This is only used for booting secondary CPUs in SMP machine
*
* Entry: CS:IP point to the start of our code, we are
* in real mode with no stack, but the rest of the
* trampoline page to make our stack and everything else
* is a mystery.
*
* In fact we don't actually need a stack so we don't
* set one up.
*
* We jump into the boot/compressed/head.S code. So you'd
* better be running a compressed kernel image or you
* won't get very far.
*
* On entry to trampoline_data, the processor is in real mode
* with 16-bit addressing and 16-bit data. CS has some value
* and IP is zero. Thus, data addresses need to be absolute
* (no relocation) and are taken with regard to r_base.
*
* If you work on this file, check the object module with
* objdump --reloc to make sure there are no relocation
* entries except for:
*
* TYPE VALUE
* R_386_32 startup_32_smp
* R_386_32 boot_gdt
*/
#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/page.h>
.data
/* We can free up trampoline after bootup if cpu hotplug is not supported. */
#ifndef CONFIG_HOTPLUG_CPU
.section ".init.data","aw",@progbits
#endif
.code16
ENTRY(trampoline_data)
r_base = .
wbinvd # Needed for NUMA-Q should be harmless for others
mov %cs, %ax # Code and data in the same place
mov %ax, %ds
cli # We should be safe anyway
movl $0xA5A5A5A5, trampoline_data - r_base
# write marker for master knows we're running
/* GDT tables in non default location kernel can be beyond 16MB and
* lgdt will not be able to load the address as in real mode default
* operand size is 16bit. Use lgdtl instead to force operand size
* to 32 bit.
*/
lidtl boot_idt_descr - r_base # load idt with 0, 0
lgdtl boot_gdt_descr - r_base # load gdt with whatever is appropriate
xor %ax, %ax
inc %ax # protected mode (PE) bit
lmsw %ax # into protected mode
# flush prefetch and jump to startup_32_smp in arch/i386/kernel/head.S
ljmpl $__BOOT_CS, $(startup_32_smp-__PAGE_OFFSET)
# These need to be in the same 64K segment as the above;
# hence we don't use the boot_gdt_descr defined in head.S
boot_gdt_descr:
.word __BOOT_DS + 7 # gdt limit
.long boot_gdt - __PAGE_OFFSET # gdt base
boot_idt_descr:
.word 0 # idt limit = 0
.long 0 # idt base = 0L
.globl trampoline_end
trampoline_end:
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