On 23/03/2021 14.14, Arnd Bergmann wrote: > From: Arnd Bergmann <arnd@xxxxxxxx> > > overlapping input and output arguments to snprintf() are > undefined behavior in C99: > Good luck: https://lore.kernel.org/lkml/1457469654-17059-1-git-send-email-linux@xxxxxxxxxxxxxxxxxx/ At least 5 years ago the consensus from old-timers was that "the kernel's snprintf supports this use case, just keep it working that way". > diff --git a/drivers/input/joystick/analog.c b/drivers/input/joystick/analog.c > index f798922a4598..8c9fed3f13e2 100644 > --- a/drivers/input/joystick/analog.c > +++ b/drivers/input/joystick/analog.c > @@ -419,14 +419,16 @@ static void analog_calibrate_timer(struct analog_port *port) > > static void analog_name(struct analog *analog) > { > - snprintf(analog->name, sizeof(analog->name), "Analog %d-axis %d-button", > + int len; > + > + len = snprintf(analog->name, sizeof(analog->name), "Analog %d-axis %d-button", > hweight8(analog->mask & ANALOG_AXES_STD), > hweight8(analog->mask & ANALOG_BTNS_STD) + !!(analog->mask & ANALOG_BTNS_CHF) * 2 + > hweight16(analog->mask & ANALOG_BTNS_GAMEPAD) + !!(analog->mask & ANALOG_HBTN_CHF) * 4); > > if (analog->mask & ANALOG_HATS_ALL) > - snprintf(analog->name, sizeof(analog->name), "%s %d-hat", > - analog->name, hweight16(analog->mask & ANALOG_HATS_ALL)); > + len += snprintf(analog->name + len, sizeof(analog->name) - len, "%d-hat", > + hweight16(analog->mask & ANALOG_HATS_ALL)); Use scnprintf, this is too fragile and hard to verify. If the first snprintf overflows, the second passes a huge size_t to snprintf which will WARN. Rasmus
