linux-kernel - Re: UBSAN: Undefined behaviour in drivers/scsi/aic7xxx/aic7xxx

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Message-ID: <1463083710.2380.46.camel@linux.vnet.ibm.com>
Date:	Thu, 12 May 2016 13:08:30 -0700
From:	James Bottomley <jejb@...ux.vnet.ibm.com>
To:	Meelis Roos <mroos@...ux.ee>, linux-scsi@...r.kernel.org,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Hannes Reinecke <hare@...e.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: UBSAN: Undefined behaviour in
 drivers/scsi/aic7xxx/aic7xxx_core.c:2831:31

On Thu, 2016-05-12 at 19:02 +0300, Meelis Roos wrote:
> This is from a dual-AthlonMP 32-bit x86 system with onboard Adaptec
> SCSI 
> controller, once during bootup.
> 
> [    4.896307]
> =====================================================================
> ===========
> [    4.896471] UBSAN: Undefined behaviour in
> drivers/scsi/aic7xxx/aic7xxx_core.c:2831:31
> [    4.896629] shift exponent -1 is negative

Is this some sort of false positive?  The shift in question is

	devinfo->target_mask = (0x01 << devinfo->target_offset);

The code which calls this in ahc_linux_initialize_scsi_bus() looks to
be looping from 0-16 (or variations).  Since the value passed in is
unsigned, it would have to be set to ~0, which doesn't seem possible.

James