Re: __attribute__((unused))

[Russell King <rmk+lkml@arm.linux.org.uk>]

On Thu, Oct 14, 2004 at 11:04:56PM +0100, David Woodhouse wrote:
> On Thu, 2004-10-14 at 22:02 +0100, Russell King wrote:
> > Hi,
> > 
> > I notice that module.h contains stuff like:
> > 
> > #define MODULE_GENERIC_TABLE(gtype,name)                        \
> > extern const struct gtype##_id __mod_##gtype##_table            \
> >   __attribute__ ((unused, alias(__stringify(name))))
> > 
> > and even:
> > 
> > #define __MODULE_INFO(tag, name, info)                                    \
> > static const char __module_cat(name,__LINE__)[]                           \
> >   __attribute_used__                                                      \
> >   __attribute__((section(".modinfo"),unused)) = __stringify(tag) "=" info
> > 
> > My understanding is that we shouldn't be using __attribute__((unused))
> > in either of these - can someone confirm.
> 
> Since the structure in question isn't explicitly referenced from
> elsewhere, the compiler may feel free to omit it. Since we want the
> compiler to emit it, not omit it, we use "unused" to say "yes, I know it
> looks unused; please emit it anyway". Later compilers use "used" to say
> "I use it really; please emit it anyway", meaning much the same thing.

It's the "later compilers" which I'm worried about here - I think they
defined "unused" to mean "this really really isn't used and you can
discard it".  Hence my concern with the above.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core