From 59c6d0ef9af5fe0daf1b95992d061a10b33e23d4 Mon Sep 17 00:00:00 2001
From: Graeme Russ <graeme.russ@gmail.com>
Date: Thu, 7 Oct 2010 20:03:21 +1100
Subject: x86: Move loading of GTD to C code

Linux has C macros and code to load the GTD after switching to Protected
Mode. Using these greatly simplifies the assembler code
---
 arch/i386/cpu/start.S | 96 ---------------------------------------------------
 1 file changed, 96 deletions(-)

(limited to 'arch/i386/cpu/start.S')

diff --git a/arch/i386/cpu/start.S b/arch/i386/cpu/start.S
index 7def8de..3cea04b 100644
--- a/arch/i386/cpu/start.S
+++ b/arch/i386/cpu/start.S
@@ -100,53 +100,6 @@ mem_init_ret:
 	jmp     get_mem_size
 get_mem_size_ret:
 
-	/*
-	 * We are now in 'Flat Protected Mode' and we know how much memory
-	 * the board has. The (temporary) Global Descriptor Table is not
-	 * in a 'Safe' place (it is either in Flash which can be erased or
-	 * reprogrammed or in a fail-safe boot-strap image which could be
-	 * over-written).
-	 *
-	 * Move the final gdt to a safe place (top of RAM) and load it.
-	 * This is not a trivial excercise - the lgdt instruction does not
-	 * have a register operand (memory only) and we may well be
-	 * running from Flash, so self modifying code will not work here.
-	 * To overcome this, we copy a stub into upper memory along with
-	 * the GDT.
-	 */
-
-	/* Reduce upper memory limit by (Stub + GDT Pointer + GDT) */
-	subl	$(end_gdt_setup - start_gdt_setup), %eax
-
-	/* Copy the GDT and Stub */
-	movl	$start_gdt_setup, %esi
-	movl	%eax, %edi
-	movl	$(end_gdt_setup - start_gdt_setup), %ecx
-	shrl	$2, %ecx
-	cld
-	rep	movsl
-
-	/* write the lgdt 'parameter' */
-	subl	$(jmp_instr - start_gdt_setup - 4), %ebp
-	addl	%eax, %ebp
-	movl	$(gdt_ptr - start_gdt_setup), %ebx
-	addl	%eax, %ebx
-	movl	%ebx, (%ebp)
-
-	/* write the gdt address into the pointer */
-	movl	$(gdt_addr - start_gdt_setup), %ebp
-	addl	%eax, %ebp
-	movl	$(gdt - start_gdt_setup), %ebx
-	addl	%eax, %ebx
-	movl	%ebx, (%ebp)
-
-	/* Save the return address */
-	movl	$load_gdt_ret, %ebp
-
-	/* Load the new (safe) Global Descriptor Table */
-	jmp	*%eax
-
-load_gdt_ret:
 	/* Check we have enough memory for stack */
 	movl	$CONFIG_SYS_STACK_SIZE, %ecx
 	cmpl	%ecx, %eax
@@ -221,52 +174,3 @@ die:	hlt
 blank_idt_ptr:
 	.word	0		/* limit */
 	.long	0		/* base */
-
-.align 4
-start_gdt_setup:
-	lgdt	gdt_ptr
-jmp_instr:
-	jmp	*%ebp
-
-.align 4
-gdt_ptr:
-	.word	0x30		/* limit (48 bytes = 6 GDT entries) */
-gdt_addr:
-	.long	gdt		/* base */
-
-	/* The GDT table ...
-	 *
-	 *	 Selector	Type
-	 *	 0x00		NULL
-	 *	 0x08		Unused
-	 *	 0x10		32bit code
-	 *	 0x18		32bit data/stack
-	 *	 0x20		16bit code
-	 *	 0x28		16bit data/stack
-	 */
-
-.align 4
-gdt:
-	.word	0, 0, 0, 0	/* NULL  */
-	.word	0, 0, 0, 0	/* unused */
-
-	.word	0xFFFF		/* 4Gb - (0x100000*0x1000 = 4Gb) */
-	.word	0		/* base address = 0 */
-	.word	0x9B00		/* code read/exec */
-	.word	0x00CF		/* granularity = 4096, 386 (+5th nibble of limit) */
-
-	.word	0xFFFF		/* 4Gb - (0x100000*0x1000 = 4Gb) */
-	.word	0x0		/* base address = 0 */
-	.word	0x9300		/* data read/write */
-	.word	0x00CF		/* granularity = 4096, 386 (+5th nibble of limit) */
-
-	.word	0xFFFF		/* 64kb */
-	.word	0		/* base address = 0 */
-	.word	0x9b00		/* data read/write */
-	.word	0x0010		/* granularity = 1  (+5th nibble of limit) */
-
-	.word	0xFFFF		/* 64kb */
-	.word	0		/* base address = 0 */
-	.word	0x9300		/* data read/write */
-	.word	0x0010		/* granularity = 1 (+5th nibble of limit) */
-end_gdt_setup:
-- 
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