Diffstat (limited to 'arch/i386/kernel/trampoline.S')
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
@@ -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
+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
+ .word __BOOT_DS + 7 # gdt limit
+ .long boot_gdt_table-__PAGE_OFFSET # gdt base
+ .word 0 # idt limit = 0
+ .long 0 # idt base = 0L