Re: why my program segmentation fault?
2008/7/14 shell909090 <shell909090@gmail.com>:
>> http://download.intel.com/design/processor/manuals/253668.pdf
>> chapter 9.1.4
>>
>> 9.1.4 First Instruction Executed
>> The first instruction that is fetched and executed following a hardware
>> reset is
>> located at physical address FFFFFFF0H. This address is 16 bytes below the
>> processor's uppermost physical address. The EPROM containing the software-
>> initialization code must be located at this address.
>> The address FFFFFFF0H is beyond the 1-MByte addressable range of the
>> processor
>> while in real-address mode. The processor is initialized to this
>> starting address as
>> follows. The CS register has two parts: the visible segment selector
>> part and the
>> hidden base address part. In real-address mode, the base address is
>> normally
>> formed by shifting the 16-bit segment selector value 4 bits to the
>> left to produce a
>> 20-bit base address. However, during a hardware reset, the segment
>> selector in the
>> CS register is loaded with F000H and the base address is loaded with
>> FFFF0000H. The
>> starting address is thus formed by adding the base address to the
>> value in the EIP
>> register (that is, FFFF0000 + FFF0H = FFFFFFF0H).
>> The first time the CS register is loaded with a new value after a
>> hardware reset, the
>> processor will follow the normal rule for address translation in
>> real-address mode
>> (that is, [CS base address = CS segment selector * 16]). To insure that
>> the base
>> address in the CS register remains unchanged until the EPROM based
>> software-
>> initialization code is completed, the code must not contain a far jump
>> or far call or
>> allow an interrupt to occur (which would cause the CS selector value
>> to be changed).
>>
>>
>>
>
> 首先纠正我刚刚话的一个错误，the base address is normally formed by shifting the 16-bit
> segment selector value 4 bits to the left to produce a 20-bit base
> address。左位移是4位，不是8位。[CS base address = CS segment selector * 16]
> 很明显，写着话的家伙是昏头了。请看这句，However, during a hardware reset, the segment selector
> in the CS register is loaded with F000H and the base address is loaded with
> FFFF0000H. The starting address is thus formed by adding the base address to
> the value in the EIP register (that is, FFFF0000 + FFF0H =
> FFFFFFF0H)。OK，大家算算，CS是F000H，左移4位，加 上FFFF0000H，算式应当是F0000H+FFFF0000H=
> 1000E0000H。后面那个算式怎么出 来的？
>
最开始的时候base的值不是按照这个rule来计算的，而是预设好的FFFF0000H,要等CS被第一次load以后才会按照这个rule计算base
--
Regards!
Star
Shanghai, China
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