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Bug 749428 - theoraenc: memory errors reported by valgrind
theoraenc: memory errors reported by valgrind
Status: RESOLVED NOTABUG
Product: GStreamer
Classification: Platform
Component: gst-plugins-base
git master
Other Linux
: Normal normal
: git master
Assigned To: GStreamer Maintainers
GStreamer Maintainers
: 749378 (view as bug list)
Depends on:
Blocks:
 
 
Reported: 2015-05-15 12:44 UTC by Guillaume Desmottes
Modified: 2015-08-19 14:22 UTC
See Also:
GNOME target: ---
GNOME version: ---


Description Guillaume Desmottes 2015-05-15 12:44:33 UTC 
Validate transcode scenarios such as validate.file.transcode.to_vorbis_and_theora_in_ogg.mp3_h264_0_mp4 raise this kind of errors when run inside valgrind:

==25715== Use of uninitialised value of size 8
==25715==    at 0x3ECCA09F1D: UnknownInlinedFun (analyze.c:1047)
==25715==    by 0x3ECCA09F1D: oc_analyze_mb_mode_chroma.isra.1 (analyze.c:1458)
==25715==    by 0x3ECCA0ADD0: oc_cost_intra.isra.2 (analyze.c:1640)
==25715==    by 0x3ECCA113FF: oc_enc_analyze_inter (analyze.c:1958)
==25715==    by 0x3ECCA1E326: oc_enc_compress_frame (encode.c:1180)
==25715==    by 0x3ECCA1E326: th_encode_ycbcr_in (encode.c:1553)
==25715==    by 0x102FA2CE: theora_enc_handle_frame (gsttheoraenc.c:989)
==25715==    by 0x55705E6: gst_video_encoder_chain (gstvideoencoder.c:1380)


==25715== Conditional jump or move depends on uninitialised value(s)
==25715==    at 0x3ECCA0A097: oc_analyze_mb_mode_chroma.isra.1 (analyze.c:1466)
==25715==    by 0x3ECCA0ADD0: oc_cost_intra.isra.2 (analyze.c:1640)
==25715==    by 0x3ECCA113FF: oc_enc_analyze_inter (analyze.c:1958)
==25715==    by 0x3ECCA1E326: oc_enc_compress_frame (encode.c:1180)
==25715==    by 0x3ECCA1E326: th_encode_ycbcr_in (encode.c:1553)
==25715==    by 0x102FA2CE: theora_enc_handle_frame (gsttheoraenc.c:989)

Those could be false positives, bugs in libtheora or in gst (if the encoder expect a specific size of buffer or something like that).
Comment 1 Tim-Philipp Müller 2015-05-17 20:02:36 UTC 
Just filing valgrind bugs where it's not even clear whether there's an issue in GStreamer or not is only useful if you intend to investigate this further.

Typically these uninitialised values are when padding between rows or planes is accessed. Encoders often do that for efficiency reasons (so they don't have to deal with 'edge' cases) if resolutions are not a multiple of their block size.

Check the exact addresses involved. Check the address of the video frame. Check the row stride and the width and the plane offsets; and calculate where the padding would be and if this is what it is or not.

Alternative add some kind in gst_video_frame_map() or wherever that initialises the padding bytes.
Comment 2 Vincent Penquerc'h 2015-05-20 08:36:31 UTC 
*** Bug 749378 has been marked as a duplicate of this bug. ***
Comment 3 Vincent Penquerc'h 2015-08-19 14:22:06 UTC 
Those valgrind errors are gone once the entire frame is memset to 0, so it does seem to be just reads off the allocated border. While the errors are from internal libtheora data, I could trace those data back to reads from the buffer.
I wasted quite some time after having not memset the full frame area, causing me to think the problem was elsewhere...