[FFmpeg-devel] [PATCH]lavc/truehd_core: Initialize the last bytes of the output buffer

[James Almer]

On 2/14/2019 5:59 PM, Carl Eugen Hoyos wrote:
> 2019-02-12 12:58 GMT+01:00, Carl Eugen Hoyos <ceffmpeg at gmail.com>:
>> Hi!
>>
>> The output of truehd_core is currently undeterministic, the last bytes
>> are uninitialized, valgrind protests if less than 8 bytes are
>> initialized.
>> I believe attached patch is simpler than calculating the necessary
>> write size at the bottom of the function.
> New patch attached.
> 
> Please comment, Carl Eugen
> 
> 
> 0001-lavc-truehd_core-Initialize-the-last-bytes-of-the-ou.patch
> 
> From f3e4231af54b7a7664e1a2224cc1223be683f93c Mon Sep 17 00:00:00 2001
> From: Carl Eugen Hoyos <ceffmpeg at gmail.com>
> Date: Thu, 14 Feb 2019 21:57:48 +0100
> Subject: [PATCH] lavc/truehd_core: Initialize the last bytes of the output
>  buffer.
> 
> Avoids undeterministic output.
> ---
>  libavcodec/truehd_core_bsf.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/libavcodec/truehd_core_bsf.c b/libavcodec/truehd_core_bsf.c
> index be021af..4760872 100644
> --- a/libavcodec/truehd_core_bsf.c
> +++ b/libavcodec/truehd_core_bsf.c
> @@ -117,6 +117,8 @@ static int truehd_core_filter(AVBSFContext *ctx, AVPacket *out)
>          out->size -= reduce * 2;
>          parity_nibble ^= out->size / 2;
>  
> +        if (out_size > 8)
> +            AV_ZERO64(out->data + out_size - 8);

AV_ZERO# may use mmx instructions. It should be safe if no float ops are
going to be used after it, otherwise an emms_c() will be needed and the
performance hit may remove any gain you get from not using memset().

An x86_32 build compiled with -mmmx or an -march value that enables mmx
should be enough to test it.

>          if (have_header) {
>              memcpy(out->data + 4, in->data + 4, 28);
>              out->data[16 + 4] = (out->data[16 + 4] & 0x0f) | (FFMIN(s->hdr.num_substreams, 3) << 4);
> -- 1.7.10.4
> 
> 
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