From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@qumranet.com>
Subject: Re: [PATCH 2/2] VMX: Reinject real mode exception
Date: Sun, 13 Jul 2008 18:28:38 +0300
Message-ID: <487A1F26.7060700@qumranet.com>
References: <4879E9C8.2010208@web.de> <4879EFAE.3080805@qumranet.com> <4879F4C0.1090609@web.de>
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Cc: kvm-devel <kvm@vger.kernel.org>,
	Mohammed Gamal <m.gamal005@gmail.com>,
	Anthony Liguori <anthony@codemonkey.ws>,
	Rik van Riel <riel@surriel.com>
To: Jan Kiszka <jan.kiszka@web.de>
Return-path: <kvm-owner@vger.kernel.org>
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Jan Kiszka wrote:
> Avi Kivity wrote:
>   
>> Jan Kiszka wrote:
>>     
> ...
>   
>>> @@ -2234,6 +2252,24 @@ static int handle_rmode_exception(struct
>>>      if (((vec == GP_VECTOR) || (vec == SS_VECTOR)) && err_code == 0)
>>>          if (emulate_instruction(vcpu, NULL, 0, 0, 0) == EMULATE_DONE)
>>>              return 1;
>>> +    /*
>>> +     * Forward all other exceptions that are valid in real mode.
>>> +     * FIXME: Breaks guest debugging in real mode, need to be fixed with
>>> +     *        the required debugging infrastructure rework.
>>> +     */
>>> +    switch (vec) {
>>> +    case DF_VECTOR:
>>> +    case SS_VECTOR:
>>> +    case GP_VECTOR:
>>> +        kvm_queue_exception_e(vcpu, vec, err_code);
>>>   
>>>       
>> These don't actually queue an error code in real mode.  Compare the
>> 'Real-Address Mode Exceptions' section with the 'Protected Mode
>> Exceptions' section  for most instructions in the Intel manual.
>>     
>
> Unless you can points out a better reference, I prefer following chapter
> 5.15 of the System Programming Guide on this. And that one doesn't make
> a difference when it says, e.g., "Exception Error Code: Zero. The
> processor always pushes an error code of 0 onto the stack of the
> doublefault handler."
>
>   

Well, xen and bochs do not push an error code for real mode #GP.  I 
tried running the attached test program but it doesn't work on real 
hardware (it does work on bochs).



-- 
error compiling committee.c: too many arguments to function


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all: real-mode-exception.iso

real-mode-exception.o: real-mode-exception.S
	as -o $@ $^

real-mode-exception.boot:  real-mode-exception.o real-mode-exception.ld
	ld -T real-mode-exception.ld -o $@ real-mode-exception.o
	dd < /dev/zero >> $@ count=2879

real-mode-exception.iso: real-mode-exception.boot
	mkisofs -o $@ -b $^ $^

--------------000506070701060700020308
Content-Type: text/plain;
 name="real-mode-exception.ld"
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Content-Disposition: inline;
 filename="real-mode-exception.ld"

OUTPUT_FORMAT(binary)

SECTIONS
{
    . = 0x7c00;
    stext = .;
    .text : { *(.init) *(.text) }
    . = ALIGN(4K);
    .data : { *(.data) }
    . = ALIGN(16);
    .bss : { *(.bss) }
    . = ALIGN(4K);
    edata = .;
}


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Content-Type: text/plain;
 name="real-mode-exception.S"
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 filename="real-mode-exception.S"

.code16

start:
	ljmp $0, $restart
restart:
	mov $0x39, %al
	mov $10, %ah
	mov $0, %bx
	mov $20, %cx
	int $0x10
	mov $0, %ax
	mov %ax, %ds
	movw $gp_handler, 13*4
	mov %cs, 13*4+2
	mov %sp, %dx
	addr32 testb $0, 0x100000
loop:	jmp loop

gp_handler:
	sub %sp, %dx
	shr $1, %dx
	add $48, %dl
	mov %dl, %al
	mov $10, %ah
	mov $0, %bx
	mov $10, %cx
	int $0x10
	jmp loop

. = 0x1fe

.byte 0x55, 0xaa


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