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, 39 insertions, 17 deletions

diff --git a/arch/x86/lib/board.c b/arch/x86/lib/board.c
index 6f075b7aa0..b64c2d3ca3 100644
--- a/arch/x86/lib/board.c
+++ b/arch/x86/lib/board.c
@@ -42,20 +42,12 @@
 #include <serial.h>
 #include <asm/u-boot-x86.h>
 #include <elf.h>
+#include <asm/processor.h>
 
 #ifdef CONFIG_BITBANGMII
 #include <miiphy.h>
 #endif
 
-/*
- * Pointer to initial global data area
- *
- * Here we initialize it.
- */
-#undef	XTRN_DECLARE_GLOBAL_DATA_PTR
-#define XTRN_DECLARE_GLOBAL_DATA_PTR	/* empty = allocate here */
-DECLARE_GLOBAL_DATA_PTR = (gd_t *) (CONFIG_SYS_INIT_GD_ADDR);
-
 /************************************************************************
  * Init Utilities							*
  ************************************************************************
@@ -128,6 +120,7 @@ static int calculate_relocation_address(void);
 static int copy_uboot_to_ram(void);
 static int clear_bss(void);
 static int do_elf_reloc_fixups(void);
+static int copy_gd_to_ram(void);
 
 init_fnc_t *init_sequence_f[] = {
 	cpu_init_f,
@@ -146,6 +139,7 @@ init_fnc_t *init_sequence_f[] = {
 };
 
 init_fnc_t *init_sequence_r[] = {
+	copy_gd_to_ram,
 	cpu_init_r,		/* basic cpu dependent setup */
 	board_early_init_r,	/* basic board dependent setup */
 	dram_init,		/* configure available RAM banks */
@@ -157,8 +151,6 @@ init_fnc_t *init_sequence_r[] = {
 	NULL,
 };
 
-gd_t *gd;
-
 static int calculate_relocation_address(void)
 {
 	ulong text_start = (ulong)&__text_start;
@@ -171,8 +163,18 @@ static int calculate_relocation_address(void)
 	 *       requirements
 	 */
 
-	/* Stack is at top of available memory */
+	/* Global Data is at top of available memory */
 	dest_addr = gd->ram_size;
+	dest_addr -= GENERATED_GBL_DATA_SIZE;
+	dest_addr &= ~15;
+	gd->new_gd_addr = dest_addr;
+
+	/* GDT is below Global Data */
+	dest_addr -= X86_GDT_SIZE;
+	dest_addr &= ~15;
+	gd->gdt_addr = dest_addr;
+
+	/* Stack is below GDT */
 	gd->start_addr_sp = dest_addr;
 
 	/* U-Boot is below the stack */
@@ -279,6 +281,31 @@ void board_init_f_r(void)
 		;
 }
 
+static int copy_gd_to_ram(void)
+{
+	gd_t *ram_gd;
+
+	/*
+	 * Global data is still in temporary memory (the CPU cache).
+	 * calculate_relocation_address() has set gd->new_gd_addr to
+	 * where the global data lives in RAM but getting it there
+	 * safely is a bit tricky due to the 'F-Segment Hack' that
+	 * we need to use for x86
+	 */
+	ram_gd = (gd_t *)gd->new_gd_addr;
+	memcpy((void *)ram_gd, gd, sizeof(gd_t));
+
+	/*
+	 * Reload the Global Descriptor Table so FS points to the
+	 * in-RAM copy of Global Data (calculate_relocation_address()
+	 * has already calculated the in-RAM location of the GDT)
+	 */
+	ram_gd->gd_addr = (ulong)ram_gd;
+	init_gd(ram_gd, (u64 *)gd->gdt_addr);
+
+	return 0;
+}
+
 void board_init_r(gd_t *id, ulong dest_addr)
 {
 #if defined(CONFIG_CMD_NET)
@@ -288,15 +315,10 @@ void board_init_r(gd_t *id, ulong dest_addr)
 	ulong size;
 #endif
 	static bd_t bd_data;
-	static gd_t gd_data;
 	init_fnc_t **init_fnc_ptr;
 
 	show_boot_progress(0x21);
 
-	/* Global data pointer is now writable */
-	gd = &gd_data;
-	memcpy(gd, id, sizeof(gd_t));
-
 	/* compiler optimization barrier needed for GCC >= 3.4 */
 	__asm__ __volatile__("" : : : "memory");