From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Andre Tanner Subject: Re: [PATCH 7/7] printk: provide a filtering macro for printk Date: Wed, 2 Sep 2009 11:54:49 +0200 Message-ID: <20090902095449.GD2736@debbook.brain-dump.org> References: <1251844269-12394-1-git-send-email-mat@brain-dump.org> <1251844269-12394-8-git-send-email-mat@brain-dump.org> <20090901233542.GA1321@shareable.org> <20090902090313.GB2736@debbook.brain-dump.org> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20090902090313.GB2736@debbook.brain-dump.org> Sender: linux-embedded-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Jamie Lokier Cc: linux-embedded@vger.kernel.org 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