I haven't had much time to work on this 'audacity' bug until today, but by tomorrow I hope to either provide draft patches that allow it to run on my system, or at least provide a more complete description of what's going wrong with the code.

I see that upstream does not allow people to open their own accounts on their Bugzilla (like X.org does), so I will need the Debian Multimedia team to mediate for me.


(I really wish that I could bisect using 'git'.  Does the 'audacity'
upstream use 'git', or do the Debian maintainers have their own 'git'
repo where they merge new versions from upstream?

    http://packages.qa.debian.org/a/audacity.html

See the VCS link on the left, there it is.

Thanks for pointing this out! I have looked at info on packages.debian.org before, but never knew about the public VCS links.

Reviewing the 'git' history, I found that the changes that break on my system were introduced in version 1.3.8.

Reviewing old emails I sent out to people, I see that the last time I used 'audacity' was mid-March 2009 (!), not any time during 2010. The date on the emails allowed me to compare with the dates in changelog.Debian.gz -- and I see now that the Debian version I last used was 1.3.7-2. The fog is clearing.


beginner with tools such as 'git' and 'gdb', but I did spend a month

Given that you have a memory issue here, I'd like to recommend valgrind.
That's a nice tool to spot out of bound access and the lot.

I haven't tried valgrind yet. The free time during the past week that I might have used debugging 'audacity' was spent reading about, and experimenting with, 'gdb'. After reading the 'info' pages, and practicing with using it on some of my own homemade software, I'm getting a feel for using it -- stepping through the code, setting break points and watch points, etc.

So far, it looks like the entire problem is limited to the changes made to open_mixer() in version 1.3.8 [file=lib-src/portmixer/src/ px_linux_alsa.c]. I won't know if there are problems beyond this function (or even the file) unless I can get open_mixer() to finish without segfaulting.

On lines 124-142 (Debian version 1.3.12-3), an attempt is made to count the number of "selems" (sound elements?) so that dynamic memory can be reserved (line 144) for a local list of structures holding information about those elements which is filled up in lines 150-222. In the loop that counts the selems, the function snd_mixer_selem_get_enum_items() repeated returns negative error codes for the first half-dozen or dozen iterations of the "elem" pointer. This causes the value of dev-> numselems to quickly add up into the negative 100's range. Later, further iterations of "elem" begin to cause dev->numselems to add up to several hundred (positive). Here is the loop in question, with problematic line 139 marked with (*):

      for (elem = snd_mixer_first_elem(dev->handle);
           elem != NULL;
           elem = snd_mixer_elem_next(elem))
      {
         if (playback) {
            if (snd_mixer_selem_has_common_volume(elem) ||
                snd_mixer_selem_has_playback_volume(elem)) {
               dev->numselems++;
            }
         }
         else {
            if (snd_mixer_selem_get_capture_group(elem) >= 0) {
               dev->numselems++;
            }
            else if (snd_mixer_selem_is_enum_capture(elem)) {
*              dev->numselems += snd_mixer_selem_get_enum_items(elem);
            }
         }
      }

Clearly, the error codes should be ignored and not added to dev-> numselems! The same sort of iteration of "elem" is made later, in the loop that fills up the array of information structures, and a very similar error in assuming there would be no error codes returned is made on line 199 (see Adrian's patch in Message #30 above on the BTS).

I need to take a break for a while, but my next experiment will be to attempt a workaround in those two loops so that any error code returned by ALSA on an "elem" pointer will cause the loop to iterate to the next "elem" (continue).


Miracle of miracles!  Version 1.3.5 runs fine on my system -- no changes

No miracle at all, they changed the code in px_linux_alsa.c. git bisect
will tell you about it.

Well, I reported that an earlier version of 'audacity' had been working for me, so I could not have meant that getting an older version to run was the miracle.

Instead, I found it miraculous that this very old version of audacity would compile on this up-to-date Sid system, with much newer versions of its dependencies than had existed back with 1.3.5 was new! (But, yes, I probably overreacted ;-)


More to come....
Dave W.



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