> This would be fine if the problem were known to be restricted to xchg(),
> but it's not. For example, on my build box ignoring the return value of
> strncmp() can in some cases trigger the same warning.
Does that happen in the tree at the moment? In any case, I guess it's not 
something we want to bite us in the bum in future!
> This is because of 
> some optimisation trickery which includes casting the return value of a
> memcpy() to char *. Because callers are usually unaware of such trickery,
> ignoring the return value of any function that produces a return value
> becomes hazardous.
Oh sorry, I see. How icky.
> Which attribute would this be? There's one to force a warning, but I don't
> believe there's one to force the opposite. Anyway, this problem is caused
> by a cast of the return value, so it's not actually a property of the C
> function itself.
Ah, I hadn't understood that it was caused by the cast in the definition of 
xchg. What a pain!
I've not actually been able to repoduce this problem in test cases with gcc 
4.0.0, so I assume it's a more recent addition - what's your compiler 
version?
Do you know if the warn_unused_result attribute will override 
the -Wno-unused-value and generate a warning anyhow? There's probably only a 
few functions we'd want this warning on - if anyone cared about switching 
these warnings off a fairly small patch could anotate the relevant ones.
Cheers,
Mark
-- 
Dave: Just a question. What use is a unicyle with no seat? And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel