On Tue, Feb 09, 2016 at 06:37:46PM -0800, Guenter Roeck wrote: > On 02/09/2016 07:26 AM, Arnd Bergmann wrote: > >On Tuesday 09 February 2016 07:08:59 Guenter Roeck wrote: > >>IS_ERR_VALUE() assumes that its parameter is an unsigned long. > >>It can not be used to check if an unsigned int reflects an error. > >>Doing so can result in the following build warning. > >> > >>drivers/tty/serial/digicolor-usart.c: In function ‘digicolor_uart_probe’: > >>include/linux/err.h:21:38: warning: > >> comparison is always false due to limited range of data type > >>drivers/tty/serial/digicolor-usart.c:485:6: note: > >> in expansion of macro ‘IS_ERR_VALUE’ > >> > >>If that warning is seen, an error return from platform_get_irq() is missed. > >> > >> > > > >The patch looks correct to me, but what compiler version and which kernel > >tree is it that triggered the warning? > > > >Andrzej Hajda just modified the definition of IS_ERR_VALUE(), and the > >changes are still under discussion, but I don't see that warning with > >any of the versions. > > > I see it with gcc 5.1 and 5.2 (and W=1). I did not see / notice Andrzej's patch. > > I agree that fixing the problem in IS_ERR_VALUE() is preferrable. I disagree. What happens if (eg) you decide to do this: u8 irq; irq = platform_get_irq(...); if (IS_ERR_VALUE(irq)) ... is that the fault of IS_ERR_VALUE() that it will never be true? No, it's a programming error in the caller, because the caller is using the wrong type here - in fact, you can't do anything in IS_ERR_VALUE() to correct that. The same is true if you assign an error value to an unsigned int: the problem is in the caller, not in IS_ERR_VALUE(). What would be preferable is if there was some way IS_ERR_VALUE() could detect if it's used on something that isn't at least a short, and is signed, but I suspect coccinelle can do that much better than trying to work out some way to get the C compiler to check that. -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
