From 7b5c3498901712dbd6503bf81c03bb6ea8e3b516 Mon Sep 17 00:00:00 2001
From: Jian Luo <jian.luo4@boschrexroth.de>
Date: Mon, 6 Jul 2015 16:42:06 +0800
Subject: [PATCH] x86: bios: Synchronize stack between real and protected mode

PCI option rom may use different SS during its execution, so it is not
safe to assume esp pointed to the same location in the protected mode.

Signed-off-by: Jian Luo <jian.luo4@boschrexroth.de>
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
---
 arch/x86/lib/bios_asm.S | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/arch/x86/lib/bios_asm.S b/arch/x86/lib/bios_asm.S
index 4faa70e314..9dbf969373 100644
--- a/arch/x86/lib/bios_asm.S
+++ b/arch/x86/lib/bios_asm.S
@@ -246,6 +246,9 @@ __interrupt_handler_16bit = PTR_TO_REAL_MODE(.)
 	push	%fs
 	push	%gs
 
+	/* Save real mode SS */
+	movw	%ss, %cs:__realmode_ss
+
 	/* Clear DF to not break ABI assumptions */
 	cld
 
@@ -258,12 +261,29 @@ __interrupt_handler_16bit = PTR_TO_REAL_MODE(.)
 
 	enter_protected_mode
 
+	/*
+	 * Now we are in protected mode. We need compute the right ESP based
+	 * on saved real mode SS otherwise interrupt_handler() won't get
+	 * correct parameters from the stack.
+	 */
+	movzwl	%cs:__realmode_ss, %ecx
+	shll	$4, %ecx
+	addl	%ecx, %esp
+
 	/* Call the C interrupt handler */
 	movl	$interrupt_handler, %eax
 	call	*%eax
 
+	/* Restore real mode ESP based on saved SS */
+	movzwl	%cs:__realmode_ss, %ecx
+	shll	$4, %ecx
+	subl	%ecx, %esp
+
 	enter_real_mode
 
+	/* Restore real mode SS */
+	movw	%cs:__realmode_ss, %ss
+
 	/*
 	 * Restore all registers, including those manipulated by the C
 	 * handler
@@ -276,6 +296,9 @@ __interrupt_handler_16bit = PTR_TO_REAL_MODE(.)
 	popal
 	iret
 
+__realmode_ss = PTR_TO_REAL_MODE(.)
+	.word	0
+
 	.globl asm_realmode_code_size
 asm_realmode_code_size:
 	.long  . - asm_realmode_code
-- 
2.39.5