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From: david@csource.oz.au (david nugent)
Newsgroups: comp.lang.c
Subject: Re: An Ubiquitous C bug
Message-ID: <851@csource.oz.au>
Date: 22 Jan 91 03:36:54 GMT
References: <s64421.664471332@zeus> <1991Jan21.083106.7297@tkou02.enet.dec.com> <2831@casbah.acns.nwu.edu>
Organization: Unique Computing Pty Ltd, Melb, Aust.
Lines: 32

In <2831@casbah.acns.nwu.edu> hpa@casbah.acns.nwu.edu (Peter Anvin) writes:

> >>This sort of program CAN print the message if x() happens to be
> >>loaded by the linker at the start of the code segment (address 0).

> All DOS compilers I know of use, in small-code models, the beginning of the
> code segment to store their startup code.

This is link order dependant; nothing whatever to do with the compiler.


> Thus, functions cannot be allocated to CS:0000h, and thus no 
> functions correspond to NULL.

Yes they can, and often are.


> The startup cod, which is written in assembler, sets up the stack, 
> local heap, floating point emulation and the arguments to main(), 
> as appropriate. main() just acts like a subroutine to the startup code.

... and can be wherever you like in the executable.


> Should NULL be all ones?

It, or an equivant, could be.

# define NULLFUNC	(int (*)()-1)


    david