On Wed, 2016-05-18 at 12:16 +0300, Andrey Ryabinin wrote: > 2016-05-18 11:18 GMT+03:00 Oliver Neukum <oneukum@xxxxxxxx>: > > On Wed, 2016-05-18 at 10:40 +0300, Andrey Ryabinin wrote: > >> 2016-05-18 1:16 GMT+03:00 Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>: > >> > On Tue, May 17, 2016 at 05:52:40PM -0400, Valdis Kletnieks wrote: > >> >> So, not content in the amount of breakage I generate already, I > >> >> compiled with UBSAN enabled... > >> >> > >> >> The immediately relevant part: > >> >> > >> >> [ 2.418576] ================================================================================ > >> >> [ 2.418579] UBSAN: Undefined behaviour in drivers/usb/host/ehci-hub.c:877:47 > >> >> [ 2.418582] index -1 is out of range for type 'u32 [1]' > >> > > >> > <snip> > >> > > >> > It's a known bug in ubsan, > >> > >> It's not a bug. int *p = &a[-1] is undefined behavior. It doesn't > >> matter whether that pointer dereferenced or not. > > > > That is a bold statement. Pointer arithmetic is defined. How can > > the computation of an address be undefined behavior while it is > > not used? > > It's defined only if pointer points to array element or one-past-end > element. Everything else is undefined. > > $ 6.5.6.8 > "If both the pointer operand and the result point to elements of > the same array object, > or one past the last element of the array object, the evaluation > shall not produce an overflow; > otherwise, the behavior is undefined." But we do not care whether the calculation overflows. We don't use it at all in those cases. Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
