Re: ["PATCH alsa-lib"] Change snd_dlopen() function to return the error string

[Takashi Iwai <tiwai@suse.de>]

On Mon, 27 Nov 2017 21:49:06 +0100,
Jaroslav Kysela wrote:
> 
> Dne 27.11.2017 v 21:24 Takashi Iwai napsal(a):
> > On Mon, 27 Nov 2017 19:19:51 +0100,
> > Takashi Sakamoto wrote:
> >>
> >> Hi Jaroslav,
> >>
> >> On Nov 27 2017 17:50, Jaroslav Kysela wrote:
> >>> The dlopen() function might fail also for another reason than
> >>> a missing file, thus return the error string from dlerror().
> >>>
> >>> Signed-off-by: Jaroslav Kysela <perex@perex.cz>
> >>> ---
> >>>   include/global.h        |  2 +-
> >>>   src/Versions.in         |  5 +++++
> >>>   src/conf.c              | 13 ++++++-----
> >>>   src/dlmisc.c            | 60 +++++++++++++++++++++++++++++++++++++++----------
> >>>   src/hwdep/hwdep.c       |  6 ++---
> >>>   src/mixer/simple_abst.c | 10 ++++-----
> >>>   src/pcm/pcm_hooks.c     |  8 +++----
> >>>   src/pcm/pcm_meter.c     |  6 ++---
> >>>   src/rawmidi/rawmidi.c   |  6 ++---
> >>>   src/seq/seq.c           |  6 ++---
> >>>   src/timer/timer.c       |  6 ++---
> >>>   src/timer/timer_query.c |  6 ++---
> >>>   12 files changed, 88 insertions(+), 46 deletions(-)
> >>
> >> Unfortunately, this patch brings build error in my environment (Ubuntu
> >> 17.10 amd64, gcc7.2.0 from gcc-7 7.2.0-8ubuntu3).
> >>
> >> $ ./gitcompile
> >> $ make
> >> make[2]: Entering directory '/tmp/alsa-lib/src'
> >>   CCLD     libasound.la
> >> /usr/bin/ld: unable to find version dependency `ALSA_1.1.6'
> >> pcm/.libs/libpcm.a(pcm_generic.o): In function `snd1_pcm_generic_hwsync':
> >> /tmp/alsa-lib/src/pcm/pcm_generic.c:142: warning:
> >> collect2: error: ld returned 1 exit status
> >> Makefile:491: recipe for target 'libasound.la' failed
> >> make[2]: *** [libasound.la] Error 1
> >>
> >> At present, I don't know exactly the reason, but I'll start
> >> investigating it in next morning (I'd like to have sleep...).
> > 
> > It's likely a bogus definition in version symbols.
> > It has to be a form like:
> > 
> >   ALSA_1.1.6 {
> >     global:
> >       @SYMBOL_PREFIX@snd_dlopen;
> >   } ALSA_1.1.5;
> > 
> > while the patch put "ALSA_1.1.6" to both places.
> 
> Yes, I forgot to modify src/Versions.in (I modified only src/Versions
> for my local build).
> 
> > Besides that, I'm scared by the versioned symbols, of which I have
> > only a bad memory.
> 
> I know, but the major issue that we forgot to apply old symbol versions
> to some functions in the past, right ? I don't see any drawback.

IIRC, some apps didn't compile the stuff properly with the versioned
symbols, thus fall back to bind with the old symbols without error,
which leads to a crash at runtime.

Another case is when an app or a library does symbol resolution by
itself via dlopen and dlsym.  libao does it, for example.

The snd_dlopen() isn't supposed to be used widely in external apps, so
maybe the influence is limited.  But I still feel bad with the usage
of versioned symbols unless really needed.  In this case, we can avoid
the issue just by adding another better function.  And, the purpose is
only for a better debuggability, so the change in caller side isn't
mandatory.


thanks,

Takashi