arch/x86/kernel/trampoline_32.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  *      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 <asm/segment.h>
  32 #include <asm/page_types.h>
  33
  34 /* We can free up trampoline after bootup if cpu hotplug is not supported. */
  35 #ifndef CONFIG_HOTPLUG_CPU
  36 .section ".cpuinit.data","aw",@progbits
  37 #else
  38 .section .rodata,"a",@progbits
  39 #endif
  40
  41 .code16
  42
  43 ENTRY(trampoline_data)
  44 r_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_descr - r_base # load idt with 0, 0
  61         lgdtl   boot_gdt_descr - 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
  71 boot_gdt_descr:
  72         .word   __BOOT_DS + 7                   # gdt limit
  73         .long   boot_gdt - __PAGE_OFFSET        # gdt base
  74
  75 boot_idt_descr:
  76         .word   0                               # idt limit = 0
  77         .long   0                               # idt base = 0L
  78
  79 .globl trampoline_end
  80 trampoline_end: