Re: GCC warnings for unused global variables

[Phil Edwards <phil at jaj dot com>]

On Fri, May 02, 2003 at 09:42:23AM -0700, Joe Buck wrote:
> On Fri, May 02, 2003 at 06:00:30PM +0200, Gabriel Dos Reis wrote:
> > | Because, since the object is volatile, it may affect the program in
> > | ways unknown to the compiler.
> > 
> > This is my favorite peeve against the definition of "volatile".
> > Does an alpha ray fired from Centauri count as a "way unknown to the
> > compiler"?
> 
> This is a much better example than you thought it was.  The answer is
> "yes".  Alpha particles are a major source of soft errors; they can
> spontaneously change the value that is stored in RAM.  Duplicated
> reads can't be eliminated because they might miss the change caused
> by the alpha particle.  A memory test might be written in C with
> a big volatile array, and one of the things it would be looking for
> is effects caused by alpha particles.
> 
> (Of course, an alpha particle can't make it through the atmosphere,
> so you'll need to pick some other particle or photon type).

Or put the platform outside the atmosphere.  These kinds of errors are
a headache for some of my colleagues.  Yes, they happen.  Yes, they use
volatile.

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