On Wed, Sep 02, 2009 at 11:03:13AM +0200, Marc Andre Tanner wrote:
> On Wed, Sep 02, 2009 at 12:35:42AM +0100, Jamie Lokier wrote:
> > Marc Andre Tanner wrote:
> > > + * The check with sizeof(void*) should make sure that we don't operate on
> > > + * pointers, which the compiler wouldn't be able to optimize out, but only
> > > + * on string constants.
> >
> > Take a look at __builtin_constant_p in the GCC manual.
> >
> > You'll probably find that wrapping the whole of the rest of the
> > expression (without the sizeof) in __builtin_constant_p is a good
> > way to know when to depend on the result of the expression.
>
> Thanks, so if I understood it correctly this should be used like this:
>
> #define PRINTK_FILTER(fmt) ( \
> (((const char *)(fmt))[0] != '<' && CONFIG_PRINTK_VERBOSITY >= 4) || \
> (((const char *)(fmt))[0] == '<' && \
> ((const char *)(fmt))[1] <= *__stringify(CONFIG_PRINTK_VERBOSITY)) \
> )
>
> #define printk(fmt, ...) ({ \
> if (__builtin_constant_p(PRINTK_FILTER(fmt)) && PRINTK_FILTER(fmt)) \
This should have been:
if (!__builtin_constant_p(PRINTK_FILTER(fmt)) || PRINTK_FILTER(fmt)) \
> printk((fmt), ##__VA_ARGS__); \
> })
>
> The sizeof check wouldn't be necessary. Is this correct?
Marc
--
Marc Andre Tanner >< http://www.brain-dump.org/ >< GPG key: CF7D56C0
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