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

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Date:	Tue, 26 Jan 2016 10:25:39 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Chris Bainbridge <chris.bainbridge@...il.com>
cc:	linux-kernel@...r.kernel.org, <aryabinin@...tuozzo.com>,
	<gregkh@...uxfoundation.org>, <linux-usb@...r.kernel.org>
Subject: Re: UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25

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?

Alan Stern