[A82] Re: TI82 ROM Version 19.006
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[A82] Re: TI82 ROM Version 19.006
On Thu, 5 Jul 2001, Dines Justesen wrote:
> A lot of programs includes images. If a program, which is supposed to
> translate ROM calls, is used on ones of these programs, how does is know
> whether the byte it finds, which looks like a call is part of an image, or
> code which is going to be executed? Try disassembling some code which
> includes data, and see how that looks afterwards.
If the program were trying to translate ROM calls, it really wouldn't be
looking for any instance of the call instruction. Instead, it would only
look for call to GET_KEY (which was constant before but unfortyunately not
in ROM 19.006) and a few other such functions, or to the ROM_CALL function
of Ash/CrASH. So you wouldn't need to think about any byte which looks
like a call, but rather any three bytes which look like a call to one of a
few specific addresses. While matching one byte by chance is quite
likely, for a three-byte sequence to be matched by chance is much less
likely. Considering the small size of TI-82 programs, it probably
shouldn't happen. Of course data in TI-82 programs isn't really "random",
but it doesn't seem (to me, anyway) that things which look like calls to
these addresses but aren't would appear more often than any other
three-byte sequences.
References: