Malloc Trouble with Large Memory Model

[Jay M. Libove]

>From article <208 at sabin.UUCP>, by bjm at sabin.UUCP (Brendan J. McMahon):
> We have never had any need for any memory module other than the 
> default small.

I'm _very_ surprised.

> We are switching to a new machine (intel 386 ) and our database libraries
> (informix) only came in the large model.
> So all programs that use these have to be compiled with -Ml2 (large model 286). 
> (Or do they?)

They do. Otherwise the loader can't deal with it. I think that
there may be some way around this, but it is much easier to
simply fix code problems that small model let's you get away
with (I'll explain below) and recompile, than it would be to
munge together different models.

> lrec[0]=(struct labelrec *)malloc(sizeof(struct labelrec));

> Compile Message:
> Warning: cast of int expression to far pointer

What's actually happenning here, most likely, is that nowhere
above the first call to malloc() was malloc() declared as an
extern function that returns type (char *) e.g.

extern char *malloc();

so the compiler is using the implicit int return rule to guess
that malloc() returns an int - which on the 8086 and 80286
compiler is a 16 bit quantity - and you're assigning the return
value of a malloc() call to a pointer - which on the 80286 and
80386 is a 32 bit quantity - and are therefore _losing_ 16
bits of address significance... I'm _really_ surprised that
you didn't get a core dump - on an 80286, you would have
gotten a core dump... my guess is that with the much larger
and better managed memory segments of the 80386, the problem
did not manifest itself as clearly as i would have on the 80286.

> Thanks for any help!
You're welcome.

> Brendan J. McMahon
> Sabin Metal Corp. |     Refiners of Precious Metals    | Hardware Trouble?
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------------- 
Jay Libove		jl42 at andrew.cmu.edu, libove at cs.cmu.edu,
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