Re: UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25

[Andrey Ryabinin]

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 practice, undefined shift just leads to undefined result of shift operation
(it depends on operands and architecture).


> Alan Stern
>