x86: Use fs for global data

Use the base address of the 'F' segment as a pointer to the global data
structure. By adding the linear address (i.e. the 'D' segment address) as
the first word of the global data structure, the address of the global data
relative to the 'D' segment can be found simply, for example, by:

	fs movl 0, %eax

This makes the gd 'pointer' writable prior to relocation (by reloading the
Global Desctriptor Table) which brings x86 into line with all other arches

NOTE: Writing to the gd 'pointer' is expensive (but we only do it
twice) but using it to access global data members (read and write) is
still fairly cheap

--
Changes for v2:
 - Rebased against changes made to patch #3
 - Removed extra indent
 - Tweaked commit message

1 files changed, 7 insertions, 1 deletions

diff --git a/arch/x86/cpu/start.S b/arch/x86/cpu/start.S
index 69a9b2c..ee0dabe 100644
--- a/arch/x86/cpu/start.S
+++ b/arch/x86/cpu/start.S
@@ -31,7 +31,7 @@
 #include <asm/global_data.h>
 #include <asm/processor.h>
 #include <asm/processor-flags.h>
-#include <generated/asm-offsets.h>
+#include <generated/generic-asm-offsets.h>
 
 .section .text
 .code32
@@ -85,6 +85,12 @@ car_init_ret:
 	 */
 	movl	$CONFIG_SYS_INIT_SP_ADDR, %esp
 
+	/* Initialise the Global Data Pointer */
+	movl	$CONFIG_SYS_INIT_GD_ADDR, %eax
+	movl	%eax, %edx
+	addl	$GENERATED_GBL_DATA_SIZE, %edx
+	call	init_gd;
+
 	/* Set parameter to board_init_f() to boot flags */
 	xorl	%eax, %eax
 	movw	%bx, %ax