Re: GCC warnings for unused global variables

[Gabriel Dos Reis <gdr at integrable-solutions dot net>]

Paul Koning <pkoning@equallogic.com> writes:

| >>>>> "Gabriel" == Gabriel Dos Reis <gdr@integrable-solutions.net> writes:
| 
|  Gabriel> Paul Koning <pkoning@equallogic.com> writes:
|  >> I can't tell if you're trying to say something that goes directly
|  >> against the intent of volatile or not, so let's talk about an
|  >> example:
| 
|  Gabriel> I'm trying to say that "volatile" is not a *reliable*
|  Gabriel> feature to use to write robust code with reproducible
|  Gabriel> behaviour.
| 
| I don't understand.
| 
| "volatile" exists in order to be able to write device drivers and
| multiprocessor applications that are robust and have reproducible
| behavior.  That's how it has always been used; that's why it exists.
| 
| Now you seem to be saying that such code is just lucky when it works.
| Why?

I gave the reasons in previous messages.  In the past, I also gave the
reasons on comp.std.c.

The key point boils down to the fact that the semantics of "volatile"
is not well-defined.  And I think I've already demonstrated that point.

[...]

| On the other hand, if you mean "it doesn't currently but at some point
| in the future gcc will start doing this because it thinks it can make

Yes, that is what I meant.

| that determination" then at that point every OS and SMP application
| will break.

Not every.  Only those that relied on (mis)fortune.

And the following quote is from someone known to have spent a certain
amount of his time on writing OSes:

   In short, "volatile" is a bad feature. It's not well-defined, and
   whatever the compiler does you can't really complain. In my opinion,
   any code that depends on volatile is almost certainly buggy as the
   standard stands now (the only case I really personally approve of is
   a "clock tick counter" kind of use)

               Linus

-- Gaby