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/* We can free up trampoline after bootup if cpu hotplug is not supported. */ 36__CPUINITRODATA 37.code16 38 39ENTRY(trampoline_data) 40r_base = . 41 wbinvd # Needed for NUMA-Q should be harmless for others 42 mov %cs, %ax # Code and data in the same place 43 mov %ax, %ds 44 45 cli # We should be safe anyway 46 47 movl $0xA5A5A5A5, trampoline_data - r_base 48 # write marker for master knows we're running 49 50 /* GDT tables in non default location kernel can be beyond 16MB and 51 * lgdt will not be able to load the address as in real mode default 52 * operand size is 16bit. Use lgdtl instead to force operand size 53 * to 32 bit. 54 */ 55 56 lidtl boot_idt_descr - r_base # load idt with 0, 0 57 lgdtl boot_gdt_descr - r_base # load gdt with whatever is appropriate 58 59 xor %ax, %ax 60 inc %ax # protected mode (PE) bit 61 lmsw %ax # into protected mode 62 # flush prefetch and jump to startup_32_smp in arch/i386/kernel/head.S 63 ljmpl $__BOOT_CS, $(startup_32_smp-__PAGE_OFFSET) 64 65 # These need to be in the same 64K segment as the above; 66 # hence we don't use the boot_gdt_descr defined in head.S 67boot_gdt_descr: 68 .word __BOOT_DS + 7 # gdt limit 69 .long boot_gdt - __PAGE_OFFSET # gdt base 70 71boot_idt_descr: 72 .word 0 # idt limit = 0 73 .long 0 # idt base = 0L 74 75.globl trampoline_end 76trampoline_end: 77