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))
\
printk((fmt), ##__VA_ARGS__);
\
})
The sizeof check wouldn't be necessary. Is this correct?
Marc
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Marc Andre Tanner >< http://www.brain-dump.org/ >< GPG key: CF7D56C0
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