On Tue, Jan 26, 2016 at 07:03:39PM +0300, Andrey Ryabinin wrote: > On 01/26/2016 06:25 PM, Alan Stern wrote: > > On Tue, 26 Jan 2016, Chris Bainbridge wrote: > > > >> Booting 4.5.0-rc1 with new UBSAN checker enabled: > >> > >> [ 4.556968] > >> ================================================================================ > >> [ 4.556972] UBSAN: Undefined behaviour in > >> drivers/usb/core/devio.c:1517:25 > >> [ 4.556975] shift exponent -1 is negative > > > > Does a left shift by a negative amount matter if the result isn't used? > > > > By definition, any code with undefined behavior could do anything.
But in reality, we are ok here, gcc isn't that foolish. > But in practice, undefined shift just leads to undefined result of shift > operation > (it depends on operands and architecture). But if we don't use the value... Anyway, please send a patch if you wish this issue to be fixed and we can discuss it that way. thanks, greg k-h
