This is C standard hair-splitting, but afaict - sum will be promoted to signed int in computation since uint8_t fits - signed overflow is undefined.
No we need to add up an awful lot of bytes to actually make it overflow. But I guess the real risk is gcc spotting this and going bananas. Fix this by simply using unsigned in to force all computations to use the well-defined unsigned behaviour.
Spotted by coverity.
v2: Simplify the entire computation as suggested by Jean.
Cc: Russell King rmk+kernel@arm.linux.org.uk Cc: Rob Clark robdclark@gmail.com Cc: Jean-Francois Moine moinejf@free.fr Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch --- drivers/gpu/drm/i2c/tda998x_drv.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c b/drivers/gpu/drm/i2c/tda998x_drv.c index 48af5cac1902..240c331405b9 100644 --- a/drivers/gpu/drm/i2c/tda998x_drv.c +++ b/drivers/gpu/drm/i2c/tda998x_drv.c @@ -568,11 +568,11 @@ static irqreturn_t tda998x_irq_thread(int irq, void *data)
static uint8_t tda998x_cksum(uint8_t *buf, size_t bytes) { - uint8_t sum = 0; + int sum = 0;
while (bytes--) - sum += *buf++; - return (255 - sum) + 1; + sum -= *buf++; + return sum; }
#define HB(x) (x)