linux-kernel - [GIT PULL] x86 setup: correct booting on 486DX4

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Message-Id: <200711042257.lA4Mvobr025200@tazenda.hos.anvin.org>
Date:	Sun, 4 Nov 2007 14:57:50 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...r.kernel.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Mikael Petterson <mikpe@...uu.se>,
	Eric Biederman <ebiederm@...ssion.com>
Subject: [GIT PULL] x86 setup: correct booting on 486DX4

Hi Linus; please pull:

  git://git.kernel.org/pub/scm/linux/kernel/git/hpa/linux-2.6-x86setup.git for-linus

H. Peter Anvin (1):
      x86 setup: correct booting on 486DX4

 arch/x86/boot/pmjump.S |   32 +++++++++++++++++++++-----------
 1 files changed, 21 insertions(+), 11 deletions(-)

[Full diff and log follows]

commit ac3b37b78c5f0f0be0b476a35370650f7bad482f
Author: H. Peter Anvin <hpa@...or.com>
Date:   Sun Nov 4 14:33:41 2007 -0800

    x86 setup: correct booting on 486DX4
    
    Apparently, the 486DX4 does not correctly serialize a mov to %cr0, so
    we really do need the far jump immediately afterwards.  This means
    losing the nice separation between 16- and 32-bit code, but c'est la
    vie.
    
    Also pass %ebx = %edi = %ebp = 0 to support future extension of the
    32-bit boot protocol.
    
    Signed-off-by: H. Peter Anvin <hpa@...or.com>

diff --git a/arch/x86/boot/pmjump.S b/arch/x86/boot/pmjump.S
index 2e55923..17e6dec 100644
--- a/arch/x86/boot/pmjump.S
+++ b/arch/x86/boot/pmjump.S
@@ -28,27 +28,37 @@
  * void protected_mode_jump(u32 entrypoint, u32 bootparams);
  */
 protected_mode_jump:
-	xorl	%ebx, %ebx		# Flag to indicate this is a boot
 	movl	%edx, %esi		# Pointer to boot_params table
-	movl	%eax, 2f		# Patch ljmpl instruction
+
+	xorl	%edx, %edx
+	movw	%cs, %dx
+	shll	$4, %edx		# Patch ljmpl instruction
+	addl	%edx, 2f
 	jmp	1f			# Short jump to flush instruction q.
 
 1:
 	movw	$__BOOT_DS, %cx
+	xorl	%ebx, %ebx		# Per protocol
+	xorl	%ebp, %ebp		# Per protocol
+	xorl	%edi, %edi		# Per protocol
 
 	movl	%cr0, %edx
 	orb	$1, %dl			# Protected mode (PE) bit
 	movl	%edx, %cr0
+	
+	.byte	0x66, 0xea		# ljmpl opcode
+2:	.long	3f			# Offset
+	.word	__BOOT_CS		# Segment
 
-	movw	%cx, %ds
-	movw	%cx, %es
-	movw	%cx, %fs
-	movw	%cx, %gs
-	movw	%cx, %ss
+	.code32
+3:
+	movl	%ecx, %ds
+	movl	%ecx, %es
+	movl	%ecx, %fs
+	movl	%ecx, %gs
+	movl	%ecx, %ss
 
 	# Jump to the 32-bit entrypoint
-	.byte	0x66, 0xea		# ljmpl opcode
-2:	.long	0			# offset
-	.word	__BOOT_CS		# segment
-
+	jmpl	*%eax
+	
 	.size	protected_mode_jump, .-protected_mode_jump
-
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