I don't know very much about the workings of transcode, or dynamic
loading, so I thought I'd
post some info here.

Transcode seems to dump core after doing a lot of work correctly, and
then it wants to initialise a plugin when there is some weird argument
corruption.

Here is some output to show what happens.

$ transcode  -H 10 -z -k -o snapshot -y ppm,null -x vob,null -i /dev/dvdrw -c 16-17 -L 75751 -q 255
transcode v0.6.12 (C) 2001-2003 Thomas Oestreich, 2003-2004 T. Bitterberg
...
(dvd_reader.c) DVD title 1/11: 36 chapter(s), 1 angle(s), title set 1
(dvd_reader.c) title playback time: 01:35:59.20  5760 sec
(dvd_reader.c) [Chapter 01] 00:00:00.000 , block from 95 to 150247
(dvd_reader.c) [Chapter 02] 00:04:35.840 , block from 150248 to 152525
...
(dvd_reader.c) [Chapter 36] 01:33:04.760 , block from 1894117 to 1980430
[transcode] (probe) suggested AV correction -D 0 (0 ms) | AV 0 ms | 0 ms
code] auto-probing source /dev/dvdrw (ok)
[transcode] V: import format    | MPEG-2 DVD PAL (V=vob|A=null)
16 frames to 17 frames 
[transcode] V: AV demux/sync    | (1) sync AV at initial MPEG sequence
[transcode] V: import frame     | 720x576  1.25:1  encoded @ 16:9
[transcode] V: flip frame       | yes
[transcode] V: rgb2bgr          | yes
[transcode] V: bits/pixel       | 0.174
[transcode] V: decoding fps,frc | 25.000,3
[transcode] A: import format    | 0x2001  AC3/A52      [48000,16,2]
[transcode] A: export           | disabled
[transcode] V: encoding fps,frc | 25.000,3
[transcode] A: language         | en
[transcode] A: bytes per frame  | 7680 (7680.000000)
[transcode] A: adjustment       | 0@1000
[transcode] encoder delay = decode=40000 encode=40000 usec
[transcode] V: video buffer     | 10 @ 720x576
[transcode] allocating 10 framebuffer (static)
loading audio import module /usr/pkg/lib/transcode/import_null.so
loading video import module /usr/pkg/lib/transcode/import_vob.so
module=tca_import [option=20, flag=255]
Bus error (core dumped)


$ gdb /usr/pkg/bin/transcode transcode.core 
GNU gdb 5.3nb1
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Type "show copying" to see the conditions.
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This GDB was configured as "x86_64--netbsd"...(no debugging symbols found)...
Core was generated by `transcode'.
Program terminated with signal 10, Bus error.
Reading symbols from /usr/libexec/ld.elf_so...(no debugging symbols found)...
done.
Loaded symbols for /usr/libexec/ld.elf_so
Reading symbols from /usr/lib/libm.so.0...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/libm.so.0
Reading symbols from /usr/lib/libpthread.so.0...(no debugging symbols found)...
done.
Loaded symbols for /usr/lib/libpthread.so.0
Reading symbols from /usr/lib/libintl.so.0...(no debugging symbols found)...
done.
Loaded symbols for /usr/lib/libintl.so.0
Reading symbols from /usr/lib/libc.so.12...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/libc.so.12
Reading symbols from /usr/pkg/lib/transcode/import_null.so...done.
Loaded symbols for /usr/pkg/lib/transcode/import_null.so
Reading symbols from /usr/pkg/lib/transcode/import_vob.so...done.
Loaded symbols for /usr/pkg/lib/transcode/import_vob.so
#0  tc_import (opt=20, para1=0x40f84cd000000000, para2=0x7f7fffffe7e0)
    at import_def.h:50
50          verbose_flag = param->flag;
(gdb) print param
No symbol "param" in current context.

Note that MOD_name is a static function that must have been inlined into 
tc_import().

(gdb) list
45      
46      MOD_name
47      {
48          static int display=0;
49          
50          verbose_flag = param->flag;
51          
52          // print module version only once
53          if(verbose_flag && (display++ == 0)) fprintf(stderr, "[%s] %s %s\n", MOD_NAME, MOD_VERSION, MOD_CODEC);
54      
(gdb) bt
#0  tc_import (opt=20, para1=0x40f84cd000000000, para2=0x7f7fffffe780)
    at import_def.h:50
#1  0x000000000041d75c in tca_import (opt=20, para1=0x7f7fffffe780, para2=0x0)
    at dl_loader.c:117
#2  0x000000000041aef4 in import_init (vob=0x73e000, 
    a_mod=0x7f7fffffe780 "\001", v_mod=0x7f7fffffee10 "vob") at decoder.c:203
#3  0x0000000000411b3f in transcoder (mode=20, vob=0x73e000) at transcode.c:564
#4  0x00000000004177dd in main (argc=-6272, argv=0x0) at transcode.c:3850

Note the difference in arguments between stack frame #0 and #1 - I think
they should just be the same, given that tca_import() calls
TCA_import(opt, para1, para2) (where TCA_import is actually a function
pointer, pointing to a module's tc_import() function).

Somehow opt is ok, para1 is some spurious extra value, and para2 is in
fact the correct value for para1 here:

(gdb) print *(transfer_t *)para2
$4 = {flag = 255, fd = 0x0, size = 0, buffer = 0x0, buffer2 = 0x0, 
  attributes = 0}

Any further ideas?

-Olaf.
-- 
___ Olaf 'Rhialto' Seibert      -- You author it, and I'll reader it.
\X/ rhialto/at/xs4all.nl        -- Cetero censeo "authored" delendum esse.