Loading and Executing Object Code at Runtime

[Sean Eric Fagan]

In article <6073 at auspex.auspex.com> guy at auspex.auspex.com (Guy Harris) writes:
>What's "data space", and how is it different from any other sort of
>space?  (Most UNIX systems run with a flat address space on 386es.  PTEs
>on the 386 only have a "writable" bit.)

Xenix had split I&D for the '386, I believe.  As for '386 unices, even those
with "flat" address spaces don't really have them; what they do is set cs
and ds (and es, and ss) to point to the same memory range.  *However*, you
still cannot execute data; you have to execute code.  Consider it as an
alias of forms.

How does this affect people?  Well, consider the following code, which is
somewhat similar to code I ran into recently:

	push	byte1
	push	byte2
	; ...
	call	@esp

Oops.  ss is a readable and writable segment, not an executable segment.
Memory-fault, core-dump.  (Note:  to make it work, all you have to do is
spit out a segment prefix [a la 'call cs:@esp'].)

Anyway, just a bunch of nit-picking, because I can't fall asleep yet...

-- 
Sean Eric Fagan  | "I made the universe, but please don't blame me for it;
sef at kithrup.COM  |  I had a bellyache at the time."
-----------------+           -- The Turtle (Stephen King, _It_)
Any opinions expressed are my own, and generally unpopular with others.