[TUHS] reviving a bit of WWB

[Steve Nickolas]

On Mon, 21 Sep 2020, John Cowan wrote:

> On Mon, Sep 21, 2020 at 1:55 AM Steve Nickolas <usotsuki at buric.co> wrote:
>
>
>> I've never written anything that uses varargs, so I've never run into
>> that.  But I've actually done quite a bit of work with an environment
>> where this isn't true: MS-DOS using the large or huge model.  In this
>> environment, sizeof(int)=2, and sizeof(void*) is 4. Of course, it's not
>> conformant to pass an int variable as an argument where a pointer variable
>> is expected.
>>
>
> If the compiler was ISO-conformant (which it almost certainly was not),
> that would not matter.  0 in int context would be a 2-byte int with all
> bits zero, and 0 in pointer context would be a 4-byte null pointer,
> probably with all bits zero.

The compiler I used at least tried to be C89. (Borland Turbo C++ 1.01)

> C doesn't require that the address represented by the null pointer (whether
> or not it is all-bits-zero) is inaccessible, merely that there is no C
> object or function there.  A simple shim of the appropriate size (1, 2, 4,
> 8 bytes depending on the CPU's alignment rules) will suffice.

Which was nice with the tiny model: a .COM file organized at near 0x0100, 
and iirc, there was guaranteed to be 0xCD 0x20 at 0x0000.  (The 8086 "INT 
20H" instruction.  I just checked in DOSEMU with PC DOS 7, and that is 
exactly what shows up there.)

"ANSI C" doesn't mean a lot though when 95% of the code I run across uses 
extensions.  I still have not successfully kitbashed the Bourne shell onto 
native DOS, OS/2 or Windows without an emulation layer - in any form.  Did 
come *pretty* close with the Forsyth shell but I couldn't work around the 
lack of fork() (OS/2 does have a near-exact counterpart for pipe(), but 
it's not exposed by the pipe() call for some reason.)  I like my Unix 
shells even on Microsoft OSes...call me crazy. ;)

-uso.