Commit e5684ec4 authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

x86, realmode: Replace open-coded ljmpw with a macro 



We cannot code an ljmpw to the real-mode segment directly, because gas
refuses to assemble an ljmp with a symbolic segment.  Instead of
open-coding it everywhere, define a macro and use it for this case.

This is specifically an ljmpw from a 16-bit segment.  This is okay, as
one should never enter real mode from a 32-bit segment: if one do, the
CPU ends up in a bizarre (and useless) mode sometimes called "unreal
mode" where segments behave like real mode but the default address and
operand sizes is 32 bits.

Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1336501366-28617-15-git-send-email-jarkko.sakkinen@intel.com
parent 968ff9ee

arch/x86/realmode/rm/realmode.h

0 → 100644
+16 −0
Original line number Diff line number Diff line 
#ifndef ARCH_X86_REALMODE_RM_REALMODE_H

#define ARCH_X86_REALMODE_RM_REALMODE_H



#ifdef __ASSEMBLY__



/*

 * 16-bit ljmpw to the real_mode_seg

 *

 * This must be open-coded since gas will choke on using a

 * relocatable symbol for the segment portion.

 */

#define LJMPW_RM(to)	.byte 0xea ; .word (to), real_mode_seg



#endif /* __ASSEMBLY__ */



#endif /* ARCH_X86_REALMODE_RM_REALMODE_H */

arch/x86/realmode/rm/reboot_32.S

+2 −4
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 
#include <linux/init.h>

#include <asm/segment.h>

#include <asm/page_types.h>

#include "realmode.h"



/*

 * The following code and data reboots the machine by switching to real
@@ -82,10 +83,7 @@ machine_real_restart_asm16: 
2:

	andb	$0x10, %dl

	movl	%edx, %cr0

	.byte	0xea			/* ljmpw */

	.word	3f			/* Offset */

	.word	real_mode_seg		/* Segment */



	LJMPW_RM(3f)

3:

	testb	$0, %al

	jz	bios

arch/x86/realmode/rm/trampoline_32.S

+2 −3
Original line number Diff line number Diff line
@@ -29,6 +29,7 @@ 
#include <linux/init.h>

#include <asm/segment.h>

#include <asm/page_types.h>

#include "realmode.h"



	.text

	.code16
@@ -38,9 +39,7 @@ 
trampoline_data:

	wbinvd			# Needed for NUMA-Q should be harmless for others



	.byte	0xea		# ljmpw

	.word	1f		# Offset

	.word	real_mode_seg	# Segment

	LJMPW_RM(1f)

1:

	mov	%cs, %ax	# Code and data in the same place

	mov	%ax, %ds

arch/x86/realmode/rm/trampoline_64.S

+2 −3
Original line number Diff line number Diff line
@@ -31,6 +31,7 @@ 
#include <asm/msr.h>

#include <asm/segment.h>

#include <asm/processor-flags.h>

#include "realmode.h"



	.text

	.balign PAGE_SIZE
@@ -40,9 +41,7 @@ ENTRY(trampoline_data) 
	cli			# We should be safe anyway

	wbinvd



	.byte	0xea		# ljmpw

	.word	1f		# Offset

	.word	real_mode_seg	# Segment

	LJMPW_RM(1f)

1:

	mov	%cs, %ax	# Code and data in the same place

	mov	%ax, %ds

arch/x86/realmode/rm/wakeup/wakeup_asm.S

+3 −6
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 
#include <asm/page_types.h>

#include <asm/pgtable_types.h>

#include <asm/processor-flags.h>

#include "../realmode.h"

#include "wakeup.h"



		.code16
@@ -36,9 +37,7 @@ wakeup_start: 
	cli

	cld



	.byte	0xea		/* ljmpw */

	.word	3f

	.word	real_mode_seg

	LJMPW_RM(3f)

3:

	/* Apparently some dimwit BIOS programmers don't know how to

	   program a PM to RM transition, and we might end up here with
@@ -59,9 +58,7 @@ wakeup_start: 


	andb	$~X86_CR0_PE, %al

	movl	%eax, %cr0

	.byte	0xea		/* ljmpw */

	.word	3f

	.word	real_mode_seg

	LJMPW_RM(3f)

3:

	/* Set up segments */

	movw	%cs, %ax