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

scott andrew franco samiam at moorecad.com
Tue Jun 18 23:10:48 CEST 2019 

Ok I see, apologies. Will try that.
 
Scott
 
--------- Original Message --------- Subject: Re: [alsa-devel] Serious bug calling ALSA lib functions from .so vs. .o file
From: "Takashi Iwai" <tiwai at suse.de>
Date: 6/18/19 1:49 pm
To: "scott andrew franco" <samiam at moorecad.com>
Cc: alsa-devel at alsa-project.org

On Tue, 18 Jun 2019 20:59:19 +0200,
 scott andrew franco wrote:
 > 
 > PS. I really appreciate the help, I have spent more than a week on this, it is a serious blocking issue.
 > 
 > I've gone over the example I posted quite carefully. I recommend you try the example out. You just need the
 > two source files below (test2.c and playwav.c). and execute the commands shown below.
 > 
 > The fact that it fails only in the .so file can explain why this bug hasn't affected more user code, since most
 > people don't call alsa from another library. However, it does not explain everything since I believe there must
 > be a few users who do put the calling code in a library.
 
 What Jaroslav pointed is to pass -lasound2 at creating the *.so file,
 not at linking to the final binary. That is,
 
 % gcc -shared test2.o -o test2.so -lasound
 
 Otherwise the linker won't get the proper versioned symbol, hence an
 incorrect symbol may be taken instead of the expected versioned one.
 
 Calling ALSA library from a shared object is commonly done,
 e.g. PulseAudio. The tricky part is the versioned symbol handling,
 and it's not specific to ALSA-lib but a generic problem.
 
 
 Takashi
 
 > 
 > Thanks,
 > 
 > Scott Franco
 > 
 > --------- Original Message --------- Subject: RE: Re: [alsa-devel] Serious bug calling ALSA lib functions from .so vs. .o file
 > From: "scott andrew franco" <samiam at moorecad.com>
 > Date: 6/18/19 11:33 am
 > To: "Jaroslav Kysela" <perex at perex.cz>
 > Cc: alsa-devel at alsa-project.org
 > 
 > 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.
 > _______________________________________________
 > Alsa-devel mailing list
 > Alsa-devel at alsa-project.org
 > https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
 > _______________________________________________
 > Alsa-devel mailing list
 > Alsa-devel at alsa-project.org
 > https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
 > 
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