From: tip-bot for Brian Gerst on
Commit-ID: 72c511dd596cff88d6523f231a0fbb8f73006d51
Gitweb: http://git.kernel.org/tip/72c511dd596cff88d6523f231a0fbb8f73006d51
Author: Brian Gerst <brgerst(a)gmail.com>
AuthorDate: Sat, 31 Jul 2010 12:48:23 -0400
Committer: H. Peter Anvin <hpa(a)zytor.com>
CommitDate: Sun, 1 Aug 2010 16:05:23 -0700

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(a)gmail.com>
LKML-Reference: <1280594903-6341-2-git-send-email-brgerst(a)gmail.com>
Signed-off-by: H. Peter Anvin <hpa(a)zytor.com>
---
arch/x86/kernel/entry_32.S | 11 +++++------
1 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index cd49141..233c582 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -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
--
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