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

[scott andrew franco]

Hi, and thanks for the reply.
 
>I think that you must link .so to -lasound, too.
 
This was done and shows in the command line example below, IE,
 
 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 that in both the "succeeds" case and the "fails" case carry the -lasound option. It would not compile
if not.
 
Scott Franco
 
--------- Original Message --------- Subject: Re: [alsa-devel] Serious bug calling ALSA lib functions from .so vs. .o file
From: "Jaroslav Kysela" <perex at perex.cz>
Date: 6/18/19 11:18 am
To: "scott andrew franco" <samiam at moorecad.com>
Cc: alsa-devel at alsa-project.org

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);
 > }
 > _______________________________________________
 > Alsa-devel mailing list
 > Alsa-devel at alsa-project.org
 > https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
 > 
 
 
 -- 
 Jaroslav Kysela <perex at perex.cz>
 Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
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