From: Derrick Stolee <stolee@gmail.com>
Date: Wed, 28 Feb 2018 20:57:26 GMT
Subject: Re: [PATCH v2] sha1_name: fix uninitialized memory errors
Message-ID: <ce8421bb-4519-c4e5-ff0a-98ae532d764b@gmail.com>
In-Reply-To: <xmqqy3jckfe3.fsf@gitster-ct.c.googlers.com>

On 2/28/2018 3:50 PM, Junio C Hamano wrote:
> Derrick Stolee <dstolee@microsoft.com> writes:
>
>> diff --git a/sha1_name.c b/sha1_name.c
>> index 611c7d24dd..a041d8d24f 100644
>> --- a/sha1_name.c
>> +++ b/sha1_name.c
>> @@ -547,15 +547,15 @@ static void find_abbrev_len_for_pack(struct packed_git *p,
>>   	 */
>>   	mad->init_len = 0;
>>   	if (!match) {
>> -		nth_packed_object_oid(&oid, p, first);
>> -		extend_abbrev_len(&oid, mad);
>> +		if (nth_packed_object_oid(&oid, p, first))
>> +			extend_abbrev_len(&oid, mad);
>>   	} else if (first < num - 1) {
>> -		nth_packed_object_oid(&oid, p, first + 1);
>> -		extend_abbrev_len(&oid, mad);
>> +		if (nth_packed_object_oid(&oid, p, first + 1))
>> +			extend_abbrev_len(&oid, mad);
>>   	}
>>   	if (first > 0) {
>> -		nth_packed_object_oid(&oid, p, first - 1);
>> -		extend_abbrev_len(&oid, mad);
>> +		if (nth_packed_object_oid(&oid, p, first - 1))
>> +			extend_abbrev_len(&oid, mad);
>>   	}
>>   	mad->init_len = mad->cur_len;
>>   }
> I do not think they are wrong, but aren't the latter two somewhat
> redundant?  "num" is p->num_objects, and we call (first+1)th element
> only after we see (first < num - 1), i.e. first+1 < num, and the
> access to (first-1)th is done only when first > 0.  The first one,
> i.e. when first points at where we _would_ find it if it existed,
> can access "first" that could be p->num_objects, so the change there
> makes sense, though.
>

Yes. But I'd rather keep the blocks consistent and use the return value 
of nth_packed_object_oid() when possible.

Thanks,
-Stolee