/* * * 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: