Re: Serious bug calling ALSA lib functions from .so vs. .o file

["scott andrew franco" <samiam@xxxxxxxxxxxx>]

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".
 
The run is:
 
samiam@samiam-home-pc:~/projects/petit_ami$ gcc -fPIC -c test2.c -o test2.o
samiam@samiam-home-pc:~/projects/petit_ami$ gcc -g3 -Iinclude linux/playwav.c ./test2.so -lasound -o playwav
samiam@samiam-home-pc:~/projects/petit_ami$ ./playwav
alsaplaywave: rate: 1
alsaplaywave: rate: 0
samiam@samiam-home-pc:~/projects/petit_ami$ gcc -g3 -Iinclude linux/playwav.c ./test2.o -lasound -o playwav
samiam@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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