Commit c4d9ba6d authored by H. Peter Anvin's avatar H. Peter Anvin Committed by Ingo Molnar
Browse files

x86 setup: make PM transition more paranoid; cleanup 32-bit entry 



Make the transition to protected mode more paranoid by having
back-to-back near jump (to synchronize the 386/486 prefetch queue) and
far jump (to set up the code segment.)

While we're at it, zero as many registers as practical (for future
expandability of the 32-bit entry interface) and enter 32-bit mode
with a valid stack.  Note that the 32-bit code cannot rely on this
stack, or we'll break all other existing users of the 32-bit
entrypoint, but it may make debugging hacks easier to write.

Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 2a6648e6

arch/x86/boot/pmjump.S

+32 −12
Original line number Diff line number Diff line
@@ -29,12 +29,13 @@ 
 */

protected_mode_jump:

	movl	%edx, %esi		# Pointer to boot_params table

	movl	%eax, 2f		# Patch ljmpl instruction



	xorl	%ebx, %ebx

	movw	%cs, %bx

	shll	$4, %ebx

	addl	%ebx, 2f



	movw	$__BOOT_DS, %cx

	xorl	%ebx, %ebx		# Per the 32-bit boot protocol

	xorl	%ebp, %ebp		# Per the 32-bit boot protocol

	xorl	%edi, %edi		# Per the 32-bit boot protocol



	movl	%cr0, %edx

	orb	$1, %dl			# Protected mode (PE) bit
@@ -42,15 +43,34 @@ protected_mode_jump: 
	jmp	1f			# Short jump to serialize on 386/486

1:



	movw	%cx, %ds

	movw	%cx, %es

	movw	%cx, %fs

	movw	%cx, %gs

	movw	%cx, %ss



	# Jump to the 32-bit entrypoint

	# Transition to 32-bit mode

	.byte	0x66, 0xea		# ljmpl opcode

2:	.long	0			# offset

2:	.long	in_pm32			# offset

	.word	__BOOT_CS		# segment



	.size	protected_mode_jump, .-protected_mode_jump



	.code32

	.type	in_pm32, @function

in_pm32:

	# Set up data segments for flat 32-bit mode

	movl	%ecx, %ds

	movl	%ecx, %es

	movl	%ecx, %fs

	movl	%ecx, %gs

	movl	%ecx, %ss

	# The 32-bit code sets up its own stack, but this way we do have

	# a valid stack if some debugging hack wants to use it.

	addl	%ebx, %esp



	# Clear registers to allow for future extensions to the

	# 32-bit boot protocol

	xorl	%ecx, %ecx

	xorl	%edx, %edx

	xorl	%ebx, %ebx

	xorl	%ebp, %ebp

	xorl	%edi, %edi



	jmpl	*%eax			# Jump to the 32-bit entrypoint



	.size	in_pm32, .-in_pm32

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