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Re: questions about relocator16.S

From: Cao jin
Subject: Re: questions about relocator16.S
Date: Thu, 16 Aug 2018 10:59:42 +0800
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Sorry I don't see reply in time because I am not on the TO or CC list.

On 08/14/2018 04:36 PM, Vladimir 'phcoder' Serbinenko wrote:
> вт, 14 авг. 2018 г., 9:11 Cao jin <address@hidden
> <mailto:address@hidden>>:
>     Hi,
>       I am learning these code, and now have 2 questions:
>     1. at the bottom of relocator_common.S, there is:
>     LOCAL(jump_vector):
>             /* Jump location. Is filled by the code */
>             .long   0
>             .long   CODE_SEGMENT
>     Since it is offset & segment selector value, why is not ".word
>     CODE_SEGMENT", is there any subtle difference?
> i386 is little endian, so effectively it just reserves 2 bytes more and
> fills them with zeros.

Yes, I think so.

>     2. in relocator16.S, after "RELOAD_GDT", the other segment registers are
>     updated two times with DATA_SEGMENT & PSEUDO_REAL_DSEG, they are pretty
>     close, there is no memory read/write between them, so why we need the
>     updates with DATA_SEGMENT?
> It's derived from older code that may have had accesses there. But it
> was tested on many CPUs and changing it risks triggering obscure bug in
> an obscure CPU

I see.

Thanks very much for your explanation, Vladimir:)

Cao jin

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