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SubjectRE: [PATCH] omap2/omapfb: make DBG() more resistant in if-else constructions
> -----Original Message-----
> From: linux-omap-owner@vger.kernel.org
> [mailto:linux-omap-owner@vger.kernel.org] On Behalf Of Niels de Vos
> Sent: Tuesday, May 10, 2011 2:51 PM
> To: linux-omap@vger.kernel.org
> Cc: linux-fbdev@vger.kernel.org;
> linux-kernel@vger.kernel.org; Niels de Vos
> Subject: [PATCH] omap2/omapfb: make DBG() more resistant in
> if-else constructions
>
> When DBG() is used in a simple if-else, the resulting code path
> currently depends on the definition of DBG(). Inserting the
> statement in
> a "do { ... } while (0)" prevents this possible misuse.
>
> Signed-off-by: Niels de Vos <ndevos@redhat.com>
>
> ---
> Note, I have not found any offenders, but a mistake can
> easily be made.
> The following example shows what can go wrong if little intention is
> paid to the definition of the DBG() macro.
>
> Example:
> if something_went_wrong()
> DBG("oh no, something went wrong!\n");
> else
> printk("all went fine\n");
>
> Old result where the else is placed inside the first if-statment:
> if something_went_wrong() {
> if (omapfb_debug) {
> printk(KERN_DEBUG "oh no, something
> went wrong!\n");
> } else {
> printk("all went fine\n");
> }
> }
>
> New result where the else is an alternative to the first if-statement:
> if something_went_wrong() {
> do {
> if (omapfb_debug)
> printk(KERN_DEBUG "oh no,
> something went wrong!\n");
> } while (0);
> } else {
> printk("all went fine\n");
> }
> ---
> drivers/video/omap2/omapfb/omapfb.h | 6 ++++--
> 1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/omap2/omapfb/omapfb.h
> b/drivers/video/omap2/omapfb/omapfb.h
> index 1305fc9..a01b0bb 100644
> --- a/drivers/video/omap2/omapfb/omapfb.h
> +++ b/drivers/video/omap2/omapfb/omapfb.h
> @@ -34,8 +34,10 @@
> #ifdef DEBUG
> extern unsigned int omapfb_debug;
> #define DBG(format, ...) \
> - if (omapfb_debug) \
> - printk(KERN_DEBUG "OMAPFB: " format, ## __VA_ARGS__)
> + do { \
> + if (omapfb_debug) \
> + printk(KERN_DEBUG "OMAPFB: " format, ##
> __VA_ARGS__); \
> + while (0)

A real good find. Wondering if it really didn't create any problems so far...

~sanjeev

> #else
> #define DBG(format, ...)
> #endif
> --
> 1.7.4.4
>
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