Re: [FFmpeg-devel] [PATCH] lavu/tx: stop using av_log(NULL, )

[Lynne via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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On 26/07/2024 10:22, Andreas Rheinhardt wrote:
> Lynne via ffmpeg-devel:
>> Its not feasible to add an AVClass in the main context, as
>> it would waste space, as the main context is recursive, and
>> every bit of assembly would need to be changed.
>>
>> While its true that on paper av_log has access to the main
>> context, that functionality is not used as no options are
>> available for setting. No options will be exposed either,
>> and it makes no sense.
>>
>> mpv has recently started warning if a NULL AVClass is used
>> as an FFmpeg bug. While I don't fully agree nor disagree with
>> this, this is a simple patch which fixes the issue.
> 
> Really?
> https://github.com/mpv-player/mpv/commit/54d0763b92f3d8239aa2258f2193eebdc74a91ef
> is 13 years old and the check would only warn if a logcontext with NULL
> AVClass* is used.

Odd, something started triggering the check on my system.

>>   libavutil/tx.c | 16 +++++++++++-----
>>   1 file changed, 11 insertions(+), 5 deletions(-)
>>
>> diff --git a/libavutil/tx.c b/libavutil/tx.c
>> index 0aae4c7cf7..136d10c374 100644
>> --- a/libavutil/tx.c
>> +++ b/libavutil/tx.c
>> @@ -30,6 +30,12 @@
>>        ((x) == AV_TX_DOUBLE_ ## type) || \
>>        ((x) == AV_TX_INT32_ ## type))
>>   
>> +static const AVClass tx_class = {
>> +    .class_name                = "tx",
>> +    .item_name                 = av_default_item_name,
>> +    .version                   = LIBAVUTIL_VERSION_INT,
>> +};
>> +
>>   /* Calculates the modular multiplicative inverse */
>>   static av_always_inline int mulinv(int n, int m)
>>   {
>> @@ -645,7 +651,7 @@ static void print_cd_info(const FFTXCodelet *cd, int prio, int len, int print_pr
>>       if (print_prio)
>>           av_bprintf(&bp, ", prio: %i", prio);
>>   
>> -    av_log(NULL, log_level, "%s\n", bp.str);
>> +    av_log((void *)&tx_class, log_level, "%s\n", bp.str);
>>   }
>>   
>>   static void print_tx_structure(AVTXContext *s, int depth)
>> @@ -653,7 +659,7 @@ static void print_tx_structure(AVTXContext *s, int depth)
>>       const FFTXCodelet *cd = s->cd_self;
>>   
>>       for (int i = 0; i <= depth; i++)
>> -        av_log(NULL, AV_LOG_DEBUG, "    ");
>> +        av_log((void *)&tx_class, AV_LOG_DEBUG, "    ");
>>   
>>       print_cd_info(cd, cd->prio, s->len, 0, AV_LOG_DEBUG);
>>   
>> @@ -818,10 +824,10 @@ av_cold int ff_tx_init_subtx(AVTXContext *s, enum AVTXType type,
>>       AV_QSORT(cd_matches, nb_cd_matches, TXCodeletMatch, cmp_matches);
>>   
>>   #if !CONFIG_SMALL
>> -    av_log(NULL, AV_LOG_TRACE, "%s\n", bp.str);
>> +    av_log((void *)&tx_class, AV_LOG_TRACE, "%s\n", bp.str);
>>   
>>       for (int i = 0; i < nb_cd_matches; i++) {
>> -        av_log(NULL, AV_LOG_TRACE, "    %i: ", i + 1);
>> +        av_log((void *)&tx_class, AV_LOG_TRACE, "    %i: ", i + 1);
>>           print_cd_info(cd_matches[i].cd, cd_matches[i].prio, 0, 1, AV_LOG_TRACE);
>>       }
>>   #endif
>> @@ -931,7 +937,7 @@ av_cold int av_tx_init(AVTXContext **ctx, av_tx_fn *tx, enum AVTXType type,
>>       *tx  = tmp.fn[0];
>>   
>>   #if !CONFIG_SMALL
>> -    av_log(NULL, AV_LOG_DEBUG, "Transform tree:\n");
>> +    av_log((void *)&tx_class, AV_LOG_DEBUG, "Transform tree:\n");
>>       print_tx_structure(*ctx, 0);
>>   #endif
>>   
> 
> Did you ever test this? av_log() expects a pointer to an AVClass-enabled
> struct, not a pointer to an AVClass. This will crash (it will interpret
> AVClass.class_name as pointer to an AVClass) when the log is active
> (when loglevel is high enough).

No, I trusted that I did test it when I submitted it a year ago.

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