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Diffstat (limited to 'arch/i386/kernel/trampoline.S')
| -rw-r--r-- | arch/i386/kernel/trampoline.S | 80 |
1 files changed, 80 insertions, 0 deletions
diff --git a/arch/i386/kernel/trampoline.S b/arch/i386/kernel/trampoline.S new file mode 100644 index 0000000..fcce0e6 --- /dev/null +++ b/arch/i386/kernel/trampoline.S @@ -0,0 +1,80 @@ +/* + * + * 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_table + */ + +#include <linux/linkage.h> +#include <asm/segment.h> +#include <asm/page.h> + +.data + +.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 - r_base # load idt with 0, 0 + lgdtl boot_gdt - 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: + .word __BOOT_DS + 7 # gdt limit + .long boot_gdt_table-__PAGE_OFFSET # gdt base + +boot_idt: + .word 0 # idt limit = 0 + .long 0 # idt base = 0L + +.globl trampoline_end +trampoline_end: |