Re: Signed int overflow behavior in the security context

[Brooks Moses <brooks dot moses at codesourcery dot com>]

Paul Schlie wrote:
> Just as:
>
>  volatile int* port = (int*)PORT_ADDRESS;
>
>  int input = *port; supposedly invoking an undefined behavior.
>
> is required to be well specified, effectively reading through a pointer
> an un-initialized object's value, and then assigning that unspecified value
> to the variable input; as otherwise the language couldn't be utilized to
> write even the most hardware drivers required of all computer systems.

Now, wait just a minute here!  Doesn't C's definition of "volatile" 
specify that things outside the program can cause the value of a 
volatile variable to become "determinate"?  It's an obvious part of what 
the term means, and Fortran's definition of volatile variables most 
certainly includes the equivalent provision.

Thus, this code is _not_ invoking an undefined behavior if something 
outside the program is causing *port to become determinate (and if the C 
standard defines "volatile" in a reasonable way).

- Brooks