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

From Andrey Ryabinin <aryabinin@virtuozzo.com>
Newsgroups linux.kernel
Subject Re: UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25
Date 2016-01-26 17:10 +0100
Message-ID <qVelS-6xm-57@gated-at.bofh.it> (permalink)
References <qVdJ9-5Zk-25@gated-at.bofh.it>
Organization linux.* mail to news gateway

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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
> 

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Thread

UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25 Chris Bainbridge <chris.bainbridge@gmail.com> - 2016-01-26 11:20 +0100
  Re: UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25 Alan Stern <stern@rowland.harvard.edu> - 2016-01-26 16:30 +0100
    Re: UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25 Andrey Ryabinin <aryabinin@virtuozzo.com> - 2016-01-26 17:10 +0100
      Re: UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25 Greg KH <gregkh@linuxfoundation.org> - 2016-01-26 17:50 +0100

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