Re: [PATCH] tag: avoid NULL pointer arithmetic

From: Jeff King <peff@peff.net>
Date: Oct 2, 2017, 19:23 UTC
Message-ID: <20171002192327.xyynkh47r2kgir7f@sigill.intra.peff.net>
In-Reply-To: <32a8b949-638a-1784-7fba-948ae32206fc@web.de>

On Mon, Oct 02, 2017 at 03:06:57PM +0200, René Scharfe wrote:

Show 12 quoted lines

> >> Avoid the ASan error by casting the results of the lookup functions to
> >> struct object pointers.  That works fine with NULL pointers as well.  We
> >> already rely on the object member being first in all object types in
> >> other places in the code.
> > 
> > Out of curiosity, did you have to do anything to coax this out of ASan
> > (e.g., a specific version)?  I've been running it pretty regularly and
> > didn't see this one (I did switch from clang to gcc a month or two ago,
> > but this code is pretty old, I think).
> 
> I did "make -j4 SANITIZE=undefined,address BLK_SHA1=1 test" with
> clang version 4.0.1-1 (tags/RELEASE_401/final), and t1450-fsck.sh failed.

Interesting. I can trigger it with the same setup, but not if:

  1. I use gcc instead of clang.

  2. If I only use one of UBSan and ASan. It's the combination that
     triggers it.

-Peff