[FFmpeg-devel] [PATCH]lavf/dashdec: Do not use memcpy() to copy a struct

Steven Liu lq at chinaffmpeg.org
Thu Apr 19 05:45:59 EEST 2018



> On 19 Apr 2018, at 03:20, wm4 <nfxjfg at googlemail.com> wrote:
> 
> On Wed, 18 Apr 2018 16:10:26 -0300
> James Almer <jamrial at gmail.com> wrote:
> 
>> On 4/18/2018 2:45 PM, Carl Eugen Hoyos wrote:
>>> Hi!
>>> 
>>> Attached patch is supposed to fix a warning (and a bug), is this the
>>> right and preferred fix?
>>> 
>>> Please comment, Carl Eugen
>>> 
>>> 
>>> 0001-lavf-dashdec-Do-not-use-memcpy-to-copy-a-struct.patch
>>> 
>>> 
>>> From cf7d2aefc1a3b3a2e9f578ede43906ed6ee96bfd Mon Sep 17 00:00:00 2001
>>> From: Carl Eugen Hoyos <ceffmpeg at gmail.com>
>>> Date: Wed, 18 Apr 2018 19:42:57 +0200
>>> Subject: [PATCH] lavf/dashdec: Do not use memcpy() to copy a struct.
>>> 
>>> Fixes a warning:
>>> libavformat/dashdec.c:1900:65: warning: argument to 'sizeof' in 'memcpy' call is the same pointer type 'struct fragment *' as the destination; expected 'struct fragment' or an explicit length
>>> ---
>>> libavformat/dashdec.c |    2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>> 
>>> diff --git a/libavformat/dashdec.c b/libavformat/dashdec.c
>>> index 6304ad9..917fb54 100644
>>> --- a/libavformat/dashdec.c
>>> +++ b/libavformat/dashdec.c
>>> @@ -1897,7 +1897,7 @@ static int init_section_compare_audio(DASHContext *c)
>>> 
>>> static void copy_init_section(struct representation *rep_dest, struct representation *rep_src)
>>> {
>>> -    memcpy(rep_dest->init_section, rep_src->init_section, sizeof(rep_src->init_section));
>>> +    rep_dest->init_section = rep_src->init_section;  
>> 
>> This would only copy the pointer. The fact memcpy was used here makes me
>> think the intention was to copy the contents of the struct, so something
>> like
>> 
>> *rep_dest->init_section = *rep_src->init_section;
>> 
>> or
>> 
>> memcpy(rep_dest->init_section, rep_src->init_section,
>> sizeof(*rep_src->init_section));
>> 
>> Would be the correct fix.
> 
> The first version would be preferable. But I think the original code
> makes no sense and was never really tested. Looking slightly closer at
> the code, init_section points to a struct that contains a further
> pointer, which would require allocating and dup'ing the memory.
> 
> Also the rep_dest->init_sec_buf allocation call isn't even checked. It
> just memcpy's to a NULL pointer. This is some seriously shit code, and
> all of dashdec.c is shit. I'd like to ask Steven Liu (who
> reviewed/pushed the patch that added this copy_init_section code) to
> _actually_ review the patches and to keep up the quality standards in
> this project (which are slightly higher than this).
Yes, that is my mistake, patch welcome and welcome you to contribute code for refine the dashdec
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Thanks
Steven







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