lkml.org 
[lkml]   [2016]   [Jan]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25
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

\
 
 \ /
  Last update: 2016-01-26 18:21    [W:0.059 / U:1.200 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site