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From: "René Scharfe" <l.s.r@web.de>
To: Jeff King <peff@peff.net>
Cc: Git List <git@vger.kernel.org>, Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH] tag: avoid NULL pointer arithmetic
Date: Mon, 2 Oct 2017 15:06:57 +0200	[thread overview]
Message-ID: <32a8b949-638a-1784-7fba-948ae32206fc@web.de> (raw)
In-Reply-To: <20171002050810.ryj4nv3nwqp7gb7p@sigill.intra.peff.net>

Am 02.10.2017 um 07:08 schrieb Jeff King:
> On Sun, Oct 01, 2017 at 04:45:13PM +0200, René Scharfe wrote:
> 
>> lookup_blob() etc. can return NULL if the referenced object isn't of the
>> expected type.  In theory it's wrong to reference the object member in
>> that case.  In practice it's OK because it's located at offset 0 for all
>> types, so the pointer arithmetic (NULL + 0) is optimized out by the
>> compiler.  The issue is reported by Clang's AddressSanitizer, though.
>>
>> 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.

René



  reply	other threads:[~2017-10-02 13:07 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-01 14:45 [PATCH] tag: avoid NULL pointer arithmetic René Scharfe
2017-10-02  4:13 ` Junio C Hamano
2017-10-02  5:08 ` Jeff King
2017-10-02 13:06   ` René Scharfe [this message]
2017-10-02 19:23     ` Jeff King
2017-10-03 10:22 ` SZEDER Gábor
2017-10-03 12:51   ` René Scharfe
2017-10-03 13:47     ` [PATCH] fsck: check results of lookup_blob() and lookup_tree() for NULL René Scharfe
2017-10-04  4:00       ` Junio C Hamano
2017-10-05 19:41         ` René Scharfe
2017-10-05 19:41       ` [PATCH v2] fsck: handle NULL return of lookup_blob() and lookup_tree() René Scharfe
2017-10-06  2:23         ` Junio C Hamano
2017-10-06 16:21           ` René Scharfe

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