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

[Carl Eugen Hoyos]

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?

Carl Eugen