linux-kernel - [PATCH 2/2] x86-32: Directly access per-cpu GDT

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Date:	Sat, 31 Jul 2010 12:48:23 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	hpa@...or.com
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] x86-32: 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@...il.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
-- 
1.7.2

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