🚀 go-pugleaf

In article <MMSHAH.92Apr14141355@im5.lcs.mit.edu>, mmshah@im.lcs.mit.edu (Milan Shah) writes:
>   Or can we? Just because the message is gone, doesn't mean that a new
>   UAE dialog isn't out there, waiting. 
> 
> I can't believe how badly misunderstood this 'No UAE' business has. Pray,
> tell me, as a programmer, how in hey do you expect *any* OS to detect 
> and correct an error in an application? What do you want Windows to do
> when you dereference a Null pointer?

 [More good examples and discussion of the UAE problem, but then he says:]

> The following program will die under every OS of the past, present, and
> future: whether you call it UAE, GPF, segmentation fault, bus error, or
> whatever. 
> 
> void main()
> {
> 	int *pnCrash;
> 
> 	pnCrash = 0;
> 	*pnCrash = 1;
> }

I can't resist the urge to make a pedantic comment (please forgive me) -
actually this program will very happily compile and run on the PDP-11
RSX system and a number of other systems.  On a lot of the PDP-11 systems
location 0 was the Directive Status Word, used to pass back status results
from system calls from the Executive to the user program.  This sequence
just sets the DSW to 1, a perfectly legal (if strange) operation for a
user program to do - in fact a 1 was the "successful completion" code for
most system calls.

But most protected-mode operating systems have deliberately unmapped
location 0 because it's so convenient for detecting the dereferencing
of a NULL pointer, so it's not a bad example, just that the quantifier
"every" is wrong (should be "most").

Apart from that minor slip (:-) your summary of this subject is quite
good.  For the most part it isn't Windows' fault that UAE's or whatever
exist, but it is (usually) Windows' fault when it allows the UAE in one
app to crash all the other apps on the system.

Bruce C. Wright