Re: questions about relocator16.S

[Vladimir 'phcoder' Serbinenko]

вт, 14 авг. 2018 г., 9:11 Cao jin <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.

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

--
Sincerely,
Cao jin



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