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>

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index cd49141cf153fb124dc46a6497dbc863a3c81ad9..233c5829e7ac066a636be430adfe19c236bf6f59 100644 (file)
--- 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