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List:       freebsd-amd64
Subject:    Re: amd64/182740: commit references a PR
From:       dfilter () FreeBSD ! ORG (dfilter service)
Date:       2013-10-10 20:00:01
Message-ID: 201310102000.r9AK01E3057971 () freefall ! freebsd ! org
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The following reply was made to PR amd64/182740; it has been noted by GNATS.

From: dfilter@FreeBSD.ORG (dfilter service)
To: bug-followup@FreeBSD.org
Cc:  
Subject: Re: amd64/182740: commit references a PR
Date: Thu, 10 Oct 2013 19:51:45 +0000 (UTC)

 Author: jhb
 Date: Thu Oct 10 19:51:38 2013
 New Revision: 256293
 URL: http://svnweb.freebsd.org/changeset/base/256293
 
 Log:
   Sanitize the %eflags returned by BIOS routines.  Some BIOS routines enter
   protected mode and may leave protected-mode-specific flags like PSL_NT set
   when they return to real mode.  This can cause a fault when BTX re-enters
   protected mode after the BIOS mode returns.
   
   PR:		amd64/182740
   Reported by:	Julian Pidancet <julian.pidancet@gmail.com>
   Approved by:	re (gjb)
   MFC after:	1 week
 
 Modified:
   head/sys/boot/i386/btx/btx/btx.S
 
 Modified: head/sys/boot/i386/btx/btx/btx.S
 ==============================================================================
 --- head/sys/boot/i386/btx/btx/btx.S	Thu Oct 10 19:48:43 2013	(r256292)
 +++ head/sys/boot/i386/btx/btx/btx.S	Thu Oct 10 19:51:38 2013	(r256293)
 @@ -41,6 +41,8 @@
  		.set PSL_RESERVED_DEFAULT,0x00000002
  		.set PSL_T,0x00000100		# Trap flag
  		.set PSL_I,0x00000200		# Interrupt enable flag
 +		.set PSL_D,0x00000400		# String instruction direction
 +		.set PSL_NT,0x00004000		# Nested task flag
  		.set PSL_VM,0x00020000		# Virtual 8086 mode flag
  		.set PSL_AC,0x00040000		# Alignment check flag
  /*
 @@ -611,8 +613,8 @@ rret_tramp:	movw $MEM_ESPR-0x08,%sp		# R
  		pushl %ds			#  regs
  		pushl %es
  		pushfl				# Save %eflags
 -		cli				# Disable interrupts
 -		std				# String ops dec
 +		pushl $PSL_RESERVED_DEFAULT|PSL_D # Use clean %eflags with
 +		popfl				#  string ops dec
  		xorw %ax,%ax			# Reset seg 
  		movw %ax,%ds			#  regs
  		movw %ax,%es			#  (%ss is already 0)
 @@ -675,6 +677,7 @@ rret_tramp.1:	xorl %ecx,%ecx			# Zero
  		testl $V86F_FLAGS,%edx		# User wants flags?
  		jz rret_tramp.3			# No
  		movl MEM_ESPR-0x3c,%eax		# Read real mode flags
 +		andl $~(PSL_T|PSL_NT),%eax	# Clear unsafe flags
  		movw %ax,-0x08(%esi)		# Update user flags (low 16)
  /*
   * Return to the user task
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