arch/x86_64/kernel/trampoline.S

   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
  34 ENTRY(trampoline_data)
  35 r_base = .
  36         wbinvd
  37         mov     %cs, %ax        # Code and data in the same place
  38         mov     %ax, %ds
  39
  40         cli                     # We should be safe anyway
  41
  42         movl    $0xA5A5A5A5, trampoline_data - r_base
  43                                 # write marker for master knows we're running
  44
  45         lidt    idt_48 - r_base # load idt with 0, 0
  46         lgdt    gdt_48 - r_base # load gdt with whatever is appropriate
  47
  48         xor     %ax, %ax
  49         inc     %ax             # protected mode (PE) bit
  50         lmsw    %ax             # into protected mode
  51         # flaush prefetch and jump to startup_32 in arch/x86_64/kernel/head.S
  52         ljmpl   $__KERNEL32_CS, $(startup_32-__START_KERNEL_map)
  53
  54         # Careful these need to be in the same 64K segment as the above;
  55 idt_48:
  56         .word   0                       # idt limit = 0
  57         .word   0, 0                    # idt base = 0L
  58
  59 gdt_48:
  60         .short  __KERNEL32_CS + 7       # gdt limit
  61         .long   cpu_gdt_table-__START_KERNEL_map
  62
  63 .globl trampoline_end
  64 trampoline_end: