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, 2 insertions, 0 deletions

diff --git a/arch/x86/include/asm/u-boot-x86.h b/arch/x86/include/asm/u-boot-x86.h
index c3d2277834..5540d51769 100644
--- a/arch/x86/include/asm/u-boot-x86.h
+++ b/arch/x86/include/asm/u-boot-x86.h
@@ -37,6 +37,8 @@ int x86_cpu_init_r(void);
 int cpu_init_r(void);
 int x86_cpu_init_f(void);
 int cpu_init_f(void);
+void init_gd(gd_t *id, u64 *gdt_addr);
+void setup_gdt(gd_t *id, u64 *gdt_addr);
 
 /* cpu/.../timer.c */
 void timer_isr(void *);