On Mon, Mar 11, 2019 at 12:10:18PM +0100, Arnd Bergmann wrote: > On Sun, Mar 10, 2019 at 10:37 AM Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > > On Thu, 7 Mar 2019 16:35:26 -0800 Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > > On Thu, Mar 7, 2019 at 1:46 PM Nathan Chancellor <natechancellor@xxxxxxxxx> wrote: > > > > > > > > When building with -Wsometimes-uninitialized, Clang warns: > > > > > > > > drivers/iio/common/ssp_sensors/ssp_iio.c:95:6: warning: variable > > > > 'calculated_time' is used uninitialized whenever 'if' condition is false > > > > [-Wsometimes-uninitialized] > > > > > > > > While it isn't wrong, this will never be a problem because > > > > iio_push_to_buffers_with_timestamp only uses calculated_time > > > > on the same condition that it is assigned (when scan_timestamp > > > > is not zero). While iio_push_to_buffers_with_timestamp is marked > > > > as inline, Clang does inlining in the optimization stage, which > > > > happens after the semantic analysis phase (plus inline is merely > > > > a hint to the compiler). > > > > > > > > Fix this by just zero initializing calculated_time. > > > > > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/394 > > > > Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx> > > > > > > Knowing that the same invariant holds across function boundaries to > > > protect access of unitialized values and thus undefined behavior > > > sounds tricky to diagnose accurately. Thanks for the patch. > > > Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > Applied to the togreg branch of iio.git and pushed out as testing > > for the autobuilders to play with it. > > > > Note this is going to be a while before it hits mainline but as > > it is a false (if reasonable!) warning I'm not going to rush > > it in as a fix. > > I think it's actually a correct warning, it just doesn't trigger > on gcc because of a known gcc bug. > > I'm not sure however why I don't see the warning with clang-8 > on my local build. Is this something I have to enable > separately? > > Arnd Yes, -Wsometimes-uninitialized is not on by default because -Wuninitialized is disabled. You can either pass it via KCFLAGS or modify scripts/Makefile.extrawarn, which is the eventual goal because Clang can catch things that GCC can't: https://github.com/ClangBuiltLinux/linux/issues/381 Cheers, Nathan
