[PATCH]x86_64: build and use GDT on copied compressed kernel 

Build and use GDT on copied compressed kernel postion, instead of using GDT 
in data segment of loaded compressed kernel. Otherwise decompressing 
compressed kernel image later in 64bit longmode, will overwrite GDT.
 
Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>

diff --git a/arch/x86_64/boot/compressed/head.S b/arch/x86_64/boot/compressed/head.S
index f9d5692..1f5ac7c 100644
--- a/arch/x86_64/boot/compressed/head.S
+++ b/arch/x86_64/boot/compressed/head.S
@@ -94,10 +94,23 @@ startup_32:
  * Prepare for entering 64 bit mode
  */
 
+/*
+ * Build early GDT table on copied compressed kernel image position, So GDT
+ * is not be overwriten when decompressing the compressed kernel. 
+ */
+	movw	$0x0020, gdt+0x00(%ebx)
+	movw	$0x0000, gdt+0x06(%ebx)
+	movl	$0x00000000, gdt+0x08(%ebx) /* NULL descriptor */
+	movl	$0x00000000, gdt+0x0c(%ebx)
+	movl	$0x0000ffff, gdt+0x10(%ebx) /* __KERNEL_CS */
+	movl	$0x00af9a00, gdt+0x14(%ebx)
+	movl	$0x0000ffff, gdt+0x18(%ebx) /* __KERNEL_DS */
+	movl	$0x00cf9200, gdt+0x1c(%ebx)
+
 	/* Load new GDT with the 64bit segments using 32bit descriptor */
-	leal	gdt(%ebp), %eax
-	movl	%eax, gdt+2(%ebp)
-	lgdt	gdt(%ebp)
+	leal	gdt(%ebx), %eax
+	movl	%eax, gdt+2(%ebx)
+	lgdt	gdt(%ebx)
 
 	/* Enable PAE mode */
 	xorl	%eax, %eax
@@ -182,7 +195,7 @@ no_longmode:
 	 * it may change in the future.
 	 */
 	.code64
-	.org 0x200
+	.org 0x400
 ENTRY(startup_64)
 	/* We come here either from startup_32 or directly from a
 	 * 64bit bootloader.  If we come here from a bootloader we depend on
@@ -287,15 +300,6 @@ relocated:
  */
 	jmp	*%rbp
 
-	.data
-gdt:
-	.word	gdt_end - gdt
-	.long	gdt
-	.word	0
-	.quad	0x0000000000000000	/* NULL descriptor */
-	.quad	0x00af9a000000ffff	/* __KERNEL_CS */
-	.quad	0x00cf92000000ffff	/* __KERNEL_DS */
-gdt_end:
 	.bss
 /* Stack for uncompression */
 	.balign 4
diff --git a/arch/x86_64/boot/compressed/vmlinux.lds b/arch/x86_64/boot/compressed/vmlinux.lds
index 94c13e5..6e041ef 100644
--- a/arch/x86_64/boot/compressed/vmlinux.lds
+++ b/arch/x86_64/boot/compressed/vmlinux.lds
@@ -36,6 +36,8 @@ SECTIONS
 		*(COMMON)
 		. = ALIGN(8);
 		_end = . ;
+		gdt = . ;
+		. = . + 8 * 4;
 		. = ALIGN(4096);
 		pgtable = . ;
 		. = . + 4096 * 6;