[alsa-devel] Serious bug calling ALSA lib functions from .so vs. .o file

[Jaroslav Kysela]

Dne 18. 06. 19 v 17:16 scott andrew franco napsal(a):
> Hello,
>  
> The issue:
>  
> calling across .so (dynamic linking) produces different behavior in ALSA library calls than normal,
> and causes ALSA to malfunction.
>  
> I have minimized my issue to as small a code section as possible. Note the code is from commonly available
> internet examples, including Free Electrons "Audio in embedded linux systems".

It seems like a linker issue. I think that you must link .so to -lasound, too.
(add -lasound to the command producing your .so library to satisfy the
versioned symbols)

						Jaroslav

>  
> The run is:
>  
> samiam at samiam-home-pc:~/projects/petit_ami$ gcc -fPIC -c test2.c -o test2.o
> samiam at samiam-home-pc:~/projects/petit_ami$ gcc -g3 -Iinclude linux/playwav.c ./test2.so -lasound -o playwav
> samiam at samiam-home-pc:~/projeclufthansa check reservationts/petit_ami$ ./playwav
> alsaplaywave: rate: 1
> alsaplaywave: rate: 0
> samiam at samiam-home-pc:~/projects/petit_ami$ gcc -g3 -Iinclude linux/playwav.c ./test2.o -lasound -o playwav
> samiam at samiam-home-pc:~/projects/petit_ami$ ./playwav
> alsaplaywave: rate: 1
> alsaplaywave: rate: 1
>   
>  Note the only difference between the two runs of "playwave" is if the second module, test2, is linked as a .so or
>  linked as a .o.
>   
>  The code is:
>  =======================================================================================
>  playwav.c
>  #include <alsa/asoundlib.h>
> #include <stdio.h>
>  void alsaplaywave1(void)
>  {
>  snd_pcm_t *pcm_handle;
>  snd_pcm_hw_params_t *params;
>  unsigned int val;
>  unsigned int rate;
>  int r;
>  /* open pcm device */
>  r = snd_pcm_open(&pcm_handle, "default", SND_PCM_STREAM_PLAYBACK, 0);
>  if (r < 0) printf("Cannot open PCM output device");
>  snd_pcm_hw_params_alloca(&params); /* get hw parameter block */
>  snd_pcm_hw_params_any(pcm_handle, params);
>  r = snd_pcm_hw_params_set_access(pcm_handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
>  if (r < 0) printf("Cannot set interleaved mode");
>  r = snd_pcm_hw_params_set_format(pcm_handle, params, SND_PCM_FORMAT_S16_LE);
>  if (r < 0) printf("Cannot set format");
>  r = snd_pcm_hw_params_set_channels(pcm_handle, params, 2);
>  if (r < 0) printf("Cannot set channels number");
>  val = 44100;
>  r = snd_pcm_hw_params_set_rate_near(pcm_handle, params, &rate, 0);
>  if (r < 0) printf("Cannot set rate");
>  snd_pcm_hw_params_get_rate(params, &rate, 0);
>  printf("alsaplaywave: rate: %d\n", rate);
>  snd_pcm_close(pcm_handle);
>  }
>  extern void alsaplaywave2(void);
>  int main(int argc, char **argv)
>  {
>  alsaplaywave1();
>  alsaplaywave2();
>  return 0;
> }
>   
>  ==================================================================================
>  test2.c
>  #include <alsa/asoundlib.h>
> #include <stdio.h>
>  void alsaplaywave2(void)
>  {
>  snd_pcm_t *pcm_handle;
>  snd_pcm_hw_params_t *params;
>  unsigned int val;
>  unsigned int rate;
>  int r;
>  /* open pcm device */
>  r = snd_pcm_open(&pcm_handle, "default", SND_PCM_STREAM_PLAYBACK, 0);
>  if (r < 0) printf("Cannot open PCM output device");
>  snd_pcm_hw_params_alloca(&params); /* get hw parameter block */
>  snd_pcm_hw_params_any(pcm_handle, params);
>  r = snd_pcm_hw_params_set_access(pcm_handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
>  if (r < 0) printf("Cannot set interleaved mode");
>  r = snd_pcm_hw_params_set_format(pcm_handle, params, SND_PCM_FORMAT_S16_LE);
>  if (r < 0) printf("Cannot set format");
>  r = snd_pcm_hw_params_set_channels(pcm_handle, params, 2);
>  if (r < 0) printf("Cannot set channels number");
>  val = 44100;
>  r = snd_pcm_hw_params_set_rate_near(pcm_handle, params, &rate, 0);
>  if (r < 0) printf("Cannot set rate");
>  snd_pcm_hw_params_get_rate(params, &rate, 0);
>  printf("alsaplaywave: rate: %d\n", rate);
>  snd_pcm_close(pcm_handle);
>  }
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-- 
Jaroslav Kysela <perex at perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.