[FFmpeg-devel] [PATCH]lavu/mem: Make alloc array functions more similar to av_malloc

[Andreas Rheinhardt]

Carl Eugen Hoyos:
> Am So., 12. Apr. 2020 um 23:58 Uhr schrieb James Almer <jamrial at gmail.com>:
>>
>> On 4/12/2020 6:53 PM, Carl Eugen Hoyos wrote:
>>> Am So., 12. Apr. 2020 um 23:52 Uhr schrieb James Almer <jamrial at gmail.com>:
>>>>
>>>> On 4/12/2020 5:55 PM, Carl Eugen Hoyos wrote:
>>>>> Am So., 12. Apr. 2020 um 22:48 Uhr schrieb James Almer <jamrial at gmail.com>:
>>>>>>
>>>>>> On 4/11/2020 8:53 PM, Carl Eugen Hoyos wrote:
>>>>>>> Am So., 12. Apr. 2020 um 00:44 Uhr schrieb Carl Eugen Hoyos
>>>>>>> <ceffmpeg at gmail.com>:
>>>>>>>>
>>>>>>>> Am So., 5. Apr. 2020 um 14:03 Uhr schrieb Michael Niedermayer
>>>>>>>> <michael at niedermayer.cc>:
>>>>>>>>>
>>>>>>>>> On Sat, Apr 04, 2020 at 12:46:36AM +0200, Carl Eugen Hoyos wrote:
>>>>>>>>>> Hi!
>>>>>>>>>>
>>>>>>>>>> Attached patch makes the alloc array functions more similar to
>>>>>>>>>> av_malloc, depending on max_alloc_size instead of INT_MAX.
>>>>>>>>>>
>>>>>>>>>> Allows a work-around for ticket #7140
>>>>>>>>>>
>>>>>>>>>> Please comment, Carl Eugen
>>>>>>>>>
>>>>>>>>>>  mem.c |    8 ++++----
>>>>>>>>>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>>>>>>>>> 507531ed6f0932834d005bc1dd7d18e762f158b2  0001-lavu-mem-Make-alloc-array-functions-more-similar-to-.patch
>>>>>>>>>> From 7ae240a9f7885130251031aba5d0764b11947fec Mon Sep 17 00:00:00 2001
>>>>>>>>>> From: Carl Eugen Hoyos <ceffmpeg at gmail.com>
>>>>>>>>>> Date: Sat, 4 Apr 2020 00:37:03 +0200
>>>>>>>>>> Subject: [PATCH] lavu/mem: Make alloc array functions more similar to
>>>>>>>>>>  av_malloc().
>>>>>>>>>>
>>>>>>>>>> Do not limit the array allocation functions to allocations of INT_MAX,
>>>>>>>>>> instead depend on max_alloc_size like av_malloc().
>>>>>>>>>>
>>>>>>>>>> Allows a workaround for ticket #7140.
>>>>>>>>>> ---
>>>>>>>>>>  libavutil/mem.c | 8 ++++----
>>>>>>>>>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>>>>>>>>
>>>>>>>>> av_size_mult() may be faster
>>>>>>>>
>>>>>>>> New patch attached.
>>>>>>>
>>>>>>> And an actually working variant.
>>>>>>>
>>>>>>> Please comment, Carl Eugen
>>>>>>
>>>>>>> From 643c501d6698d7d17e47a9f907165649f1446fa6 Mon Sep 17 00:00:00 2001
>>>>>>> From: Carl Eugen Hoyos <ceffmpeg at gmail.com>
>>>>>>> Date: Sun, 12 Apr 2020 00:36:30 +0200
>>>>>>> Subject: [PATCH] lavu/mem: Make other alloc functions more similar to av_malloc().
>>>>>>>
>>>>>>> Do not limit the array allocation functions and av_calloc() to allocations
>>>>>>> of INT_MAX, instead depend on max_alloc_size like av_malloc().
>>>>>>>
>>>>>>> Allows a workaround for ticket #7140.
>>>>>>> ---
>>>>>>>  libavutil/mem.c | 20 ++++++++++++--------
>>>>>>>  1 file changed, 12 insertions(+), 8 deletions(-)
>>>>>>>
>>>>>>> diff --git a/libavutil/mem.c b/libavutil/mem.c
>>>>>>> index 88fe09b179..e044374c62 100644
>>>>>>> --- a/libavutil/mem.c
>>>>>>> +++ b/libavutil/mem.c
>>>>>>> @@ -183,23 +183,26 @@ int av_reallocp(void *ptr, size_t size)
>>>>>>>
>>>>>>>  void *av_malloc_array(size_t nmemb, size_t size)
>>>>>>>  {
>>>>>>> -    if (!size || nmemb >= INT_MAX / size)
>>>>>>> +    size_t result;
>>>>>>> +    if (av_size_mult(nmemb, size, &result) < 0)
>>>>>>>          return NULL;
>>>>>>> -    return av_malloc(nmemb * size);
>>>>>>> +    return av_malloc(result);
>>>>>>
>>>>>> If I'm reading this right, when size is 0, instead of NULL this will now
>>>>>> return av_malloc(0), which looks like it may end up being a pointer to a
>>>>>> 1 byte big buffer. Is that intended?
>>>>>>
>>>>>> The previous version you sent apparently considered that scenario.
>>>>>
>>>>> But it did not pass fate because the behaviour before the patch
>>>>> was not to return NULL for alloc(0).
>>>>
>>>> Before this patch it would return NULL when size was 0 and alloc(0) when
>>>> nmemb was 0. Now it will return alloc(0) when either of the two
>>>> arguments is 0.
>>>>
>>>> The check should be (!size || av_size_mult(nmemb, size, &result) < 0) or
>>>> similar instead, if we want to keep the original behavior.
>>>
>>> How did the original behaviour make any sense?
>>
>> Not saying it made sense, i'm saying we changed that behavior when the
>> patch, at least based on the description, only tried to replace the
>> INT_MAX limit with max_alloc_size.
>>
>> If making size 0 return malloc(0) was intended, or ultimately preferred,
>> then I'll not oppose to it.
> 
> To me, the old behaviour (returning NULL for some argument being 0
> but not the other) made less sense than the new behaviour (not
> special-casing 0 for any argument).
> The fact that returning NULL broke fate surprised me but I failed
> to find the reason.
> 
Which tests failed?

- Andreas