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

18 Jun 2019


      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@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:~/projeclufthansa check reservationts/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 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@perex.cz
Date: 6/18/19 11:18 am
To: "scott andrew franco" samiam@moorecad.com
Cc: alsa-devel@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@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:~/projeclufthansa check reservationts/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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-- 
 Jaroslav Kysela perex@perex.cz
 Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
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