[Qemu-devel] Re: [PATCH 1/5] Suppress some gcc warnings with -Wtype-limits

[Michael S. Tsirkin]

On Sat, Sep 04, 2010 at 05:21:24PM +0000, Blue Swirl wrote:
> In the unsigned number space, the checks can be merged into one,
> assuming that BLKDBG_EVEN_MAX is less than INT_MAX. Alternatively we
> could have:
>  -    if (event < 0 || event >= BLKDBG_EVENT_MAX) {
>  +    if ((int)event < 0 || event >= BLKDBG_EVENT_MAX) {
> 
> This would also implement the check that the writer of this code was
> trying to make.
> The important thing to note is however is that the check as it is now
> is not correct.

I agree. But it seems to indicate a bigger problem.

If we are trying to pass in a negative value, which is not one
of enum values, using BlkDebugEvent as type is just confusing,
we should just pass int instead.


> >> How about adding assert(OMAP_EMIFS_BASE == 0) and commenting out the
> >> check? Then if the value changes, the need to add the comparison back
> >> will be obvious.
> >
> > This would work but it's weird.  The thing is it's currently a correct
> > code and the check may be useless but it's the optimiser's task to
> > remove it, not ours.  The compiler is not able to tell whether the
> > check makes sense or nott, because the compiler only has access to
> > preprocessed code.  So why should you let the compiler have anything
> > to say on it.
> 
> Good point. I'll try to invent something better.

Use #pragma to supress the warning? Maybe we could wrap this in a macro ..

-- 
MST