Shouldn't invalid references like this fail at compile time?

[Mike Franklin]

On Thursday, 25 January 2018 at 02:41:53 UTC, Walter Bright wrote:

>
> Ok, but are these devices with 0 being a valid address?
>
> It seems weird to me that any sane modern CPU design that can 
> access megabytes of memory would have 0 be a valid address.

Yes, 0 is a valid address and typically points to ROM 
(http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0497a/CHDBIJJE.html).

"The initial stack pointer and the address of the reset handler 
must be located at 0x0 and 0x4 respectively." 
(http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0497a/CHDBIJJE.html)

So you read address 0, dereference it, and you're at the bottom 
of the stack.

Some microcontrollers have an MPU to mitigate this.  You can read 
one technique here:  
http://nuttx.org/doku.php?id=wiki:howtos:stm32-null-pointer  But 
the MPU is an optional component, and many microcontrollers in 
the ARM Cortex-M family do not have one.

Mike