From owner-freebsd-current  Fri Jul  5 20: 3:11 2002
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Date: Fri, 5 Jul 2002 20:03:06 -0700 (PDT)
From: David Xu <bsddiy@yahoo.com>
Subject: Re: i386 trap code
To: Julian Elischer <julian@elischer.org>
Cc: Peter Wemm <peter@wemm.org>,
	FreeBSD current users <current@FreeBSD.ORG>
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----- Original Message ----- 
From: "Julian Elischer" <julian@elischer.org>
To: "Peter Wemm" <peter@wemm.org>
Cc: "FreeBSD current users" <current@FreeBSD.ORG>
Sent: Saturday, July 06, 2002 8:43 AM
Subject: i386 trap code


> 
> Looking at i386/exception.s
> one sees:
> ###################################
>         .globl  alltraps
>         .type   alltraps,@function
> alltraps:
>         pushal
>         pushl   %ds
>         pushl   %es
>         pushl   %fs
> alltraps_with_regs_pushed:
>         mov     $KDSEL,%ax
>         mov     %ax,%ds
>         mov     %ax,%es
>         mov     $KPSEL,%ax
>         mov     %ax,%fs
>         FAKE_MCOUNT(13*4(%esp))
> calltrap:
>         FAKE_MCOUNT(btrap)              /* init "from" btrap -> calltrap
> */
>         call    trap
> 
>         /*
>          * Return via doreti to handle ASTs.
>          */
>         MEXITCOUNT
>         jmp     doreti
> #######################################
> 
> but one has to look in isa/ipl.s to find:
> ########################################
>         SUPERALIGN_TEXT
>         .type   doreti,@function
> doreti:
>         FAKE_MCOUNT(bintr)              /* init "from" bintr -> doreti */
> doreti_next:
>         /*
>          * Check if ASTs can be handled now.  PSL_VM must be checked first
>          * since segment registers only have an RPL in non-VM86 mode.
>          */
>         testl   $PSL_VM,TF_EFLAGS(%esp) /* are we in vm86 mode? */
>         jz      doreti_notvm86
>         cmpl    $1,in_vm86call          /* are we in a vm86 call? */

sorry for a bit OT, does anyone see this in_vm86call crazy global variable?
it prevents two CPUs to trap into VM86 model :(
if you have interest in fixing this problem,  please have a look at PR :

http://www.freebsd.org/cgi/query-pr.cgi?pr=i386/38223

I have also fixed the problem that VM86 call is preempted by interrupt
threads and causes system crash. newest patch can always be gotten from :
http://opensource.zjonline.com.cn/freebsd/vm86patch.tgz

-David Xu


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