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-rw-r--r--i386/i386at/boothdr.S37
1 files changed, 37 insertions, 0 deletions
diff --git a/i386/i386at/boothdr.S b/i386/i386at/boothdr.S
index 45cd599..567851e 100644
--- a/i386/i386at/boothdr.S
+++ b/i386/i386at/boothdr.S
@@ -39,6 +39,19 @@ boot_hdr:
#endif /* __ELF__ */
boot_entry:
+ /* use segmentation to offset ourself. */
+ lgdt boot_gdt_descr - KERNELBASE
+ ljmp $8,$0f
+0:
+ movw $0,%ax
+ movw %ax,%ds
+ movw %ax,%es
+ movw %ax,%fs
+ movw %ax,%gs
+ movw $16,%ax
+ movw %ax,%ds
+ movw %ax,%es
+ movw %ax,%ss
/* Switch to our own interrupt stack. */
movl $_intstack+INTSTACK_SIZE,%esp
@@ -80,3 +93,27 @@ iplt_done:
.comm _intstack,INTSTACK_SIZE
+.align 16
+ .word 0
+boot_gdt_descr:
+ .word 3*8+7
+ .long boot_gdt - KERNELBASE
+.align 16
+boot_gdt:
+ /* 0 */
+ .quad 0
+ /* boot CS = 8 */
+ .word 0xffff
+ .word (-KERNELBASE) & 0xffff
+ .byte ((-KERNELBASE) >> 16) & 0xff
+ .byte 0x9a
+ .byte 0xcf
+ .byte ((-KERNELBASE) >> 24) & 0xff
+ /* boot DS = 8 */
+ .word 0xffff
+ .word (-KERNELBASE) & 0xffff
+ .byte ((-KERNELBASE) >> 16) & 0xff
+ .byte 0x92
+ .byte 0xcf
+ .byte ((-KERNELBASE) >> 24) & 0xff
+