Messages in this thread | | | Date | Tue, 26 Jan 2016 08:43:54 -0800 | From | Greg KH <> | Subject | Re: UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25 |
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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
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