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x86-32, asm: Directly access per-cpu GDT 

Use a direct per-cpu reference for the GDT instead of using a scratch
register.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
LKML-Reference: <1280594903-6341-2-git-send-email-brgerst@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Brian Gerst 2010-07-31 12:48:23 -04:00 committed by H. Peter Anvin
parent c15a5958a0
commit 72c511dd59
1 changed files with 5 additions and 6 deletions
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11
arch/x86/kernel/entry_32.S
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@ -611,14 +611,14 @@ ldt_ss:
* compensating for the offset by changing to the ESPFIX segment with
* a base address that matches for the difference.
*/
#define GDT_ESPFIX_SS PER_CPU_VAR(gdt_page) + (GDT_ENTRY_ESPFIX_SS * 8)
mov %esp, %edx /* load kernel esp */
mov PT_OLDESP(%esp), %eax /* load userspace esp */
mov %dx, %ax /* eax: new kernel esp */
sub %eax, %edx /* offset (low word is 0) */
PER_CPU(gdt_page, %ebx)
shr $16, %edx
mov %dl, GDT_ENTRY_ESPFIX_SS * 8 + 4(%ebx) /* bits 16..23 */
mov %dh, GDT_ENTRY_ESPFIX_SS * 8 + 7(%ebx) /* bits 24..31 */
mov %dl, GDT_ESPFIX_SS + 4 /* bits 16..23 */
mov %dh, GDT_ESPFIX_SS + 7 /* bits 24..31 */
pushl $__ESPFIX_SS
CFI_ADJUST_CFA_OFFSET 4
push %eax /* new kernel esp */
@ -791,9 +791,8 @@ ptregs_clone:
* normal stack and adjusts ESP with the matching offset.
*/
/* fixup the stack */
PER_CPU(gdt_page, %ebx)
mov GDT_ENTRY_ESPFIX_SS * 8 + 4(%ebx), %al /* bits 16..23 */
mov GDT_ENTRY_ESPFIX_SS * 8 + 7(%ebx), %ah /* bits 24..31 */
mov GDT_ESPFIX_SS + 4, %al /* bits 16..23 */
mov GDT_ESPFIX_SS + 7, %ah /* bits 24..31 */
shl $16, %eax
addl %esp, %eax /* the adjusted stack pointer */
pushl $__KERNEL_DS