| Message ID | 20190307214546.9624-1-natechancellor@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | iio: common: ssp_sensors: Initialize calculated_time in ssp_common_process_data | expand |
On Thu, Mar 7, 2019 at 1:46 PM Nathan Chancellor <natechancellor@gmail.com> 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@gmail.com> 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@google.com> > --- > drivers/iio/common/ssp_sensors/ssp_iio.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/iio/common/ssp_sensors/ssp_iio.c b/drivers/iio/common/ssp_sensors/ssp_iio.c > index 645f2e3975db..e38f704d88b7 100644 > --- a/drivers/iio/common/ssp_sensors/ssp_iio.c > +++ b/drivers/iio/common/ssp_sensors/ssp_iio.c > @@ -81,7 +81,7 @@ int ssp_common_process_data(struct iio_dev *indio_dev, void *buf, > unsigned int len, int64_t timestamp) > { > __le32 time; > - int64_t calculated_time; > + int64_t calculated_time = 0; > struct ssp_sensor_data *spd = iio_priv(indio_dev); > > if (indio_dev->scan_bytes == 0) > -- > 2.21.0 >
On Thu, 7 Mar 2019 16:35:26 -0800 Nick Desaulniers <ndesaulniers@google.com> wrote: > On Thu, Mar 7, 2019 at 1:46 PM Nathan Chancellor > <natechancellor@gmail.com> 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@gmail.com> > > 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@google.com> 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. Thanks, Jonathan > > > --- > > drivers/iio/common/ssp_sensors/ssp_iio.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/iio/common/ssp_sensors/ssp_iio.c b/drivers/iio/common/ssp_sensors/ssp_iio.c > > index 645f2e3975db..e38f704d88b7 100644 > > --- a/drivers/iio/common/ssp_sensors/ssp_iio.c > > +++ b/drivers/iio/common/ssp_sensors/ssp_iio.c > > @@ -81,7 +81,7 @@ int ssp_common_process_data(struct iio_dev *indio_dev, void *buf, > > unsigned int len, int64_t timestamp) > > { > > __le32 time; > > - int64_t calculated_time; > > + int64_t calculated_time = 0; > > struct ssp_sensor_data *spd = iio_priv(indio_dev); > > > > if (indio_dev->scan_bytes == 0) > > -- > > 2.21.0 > > > >
On Sun, Mar 10, 2019 at 10:37 AM Jonathan Cameron <jic23@kernel.org> wrote: > On Thu, 7 Mar 2019 16:35:26 -0800 Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Thu, Mar 7, 2019 at 1:46 PM Nathan Chancellor <natechancellor@gmail.com> 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@gmail.com> > > > > 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@google.com> > 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
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@kernel.org> wrote: > > On Thu, 7 Mar 2019 16:35:26 -0800 Nick Desaulniers <ndesaulniers@google.com> wrote: > > > On Thu, Mar 7, 2019 at 1:46 PM Nathan Chancellor <natechancellor@gmail.com> 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@gmail.com> > > > > > > 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@google.com> > > 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
diff --git a/drivers/iio/common/ssp_sensors/ssp_iio.c b/drivers/iio/common/ssp_sensors/ssp_iio.c index 645f2e3975db..e38f704d88b7 100644 --- a/drivers/iio/common/ssp_sensors/ssp_iio.c +++ b/drivers/iio/common/ssp_sensors/ssp_iio.c @@ -81,7 +81,7 @@ int ssp_common_process_data(struct iio_dev *indio_dev, void *buf, unsigned int len, int64_t timestamp) { __le32 time; - int64_t calculated_time; + int64_t calculated_time = 0; struct ssp_sensor_data *spd = iio_priv(indio_dev); if (indio_dev->scan_bytes == 0)
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@gmail.com> --- drivers/iio/common/ssp_sensors/ssp_iio.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)