[Buildroot] abi problem with arm [solves alsa-lib invalid ioctl]

[Ivan Kuten <ivan.kuten@promwad.com>]

ing. Federico Fuga wrote:
> Hi,
> 
> I have found and solved the problem that breaks the ioctl of alsa-lib in
> arm.
> Just a little preamble:
> 
> when compiling with arm xscale on an em-x270 board, all the installation
> works correctly except that the alsactl cannot set the volume levels of
> mixer:
> 
> # alsactl restore
> unknown ioctl = 0xc2c45513 ioctl ELEM_WRITE=0xc2c85513 struct 712
> alsactl: set_control:1159: Cannot write control '2:0:0:Speaker Playback
> Volume:0' : Inappropriate ioctl for device
> 
> (note that the "unknown ioctl" message is a debug message i put on the
> sound/core/control.c source to get rid of the problem).
> If you compile a simple program that prints the ioctl and sizeof struct
> snd_ctl_elem_value, you'll notice that the structure size is 708 in this
> case.
> As someone pointed out, there may be an alignment problem problem in the
> structure when compiled with the toolchain.
> The strange thing is that a kernel compiled with this toolchain
> (arm-linux-uclibc) works perfectly with all programs except that alsa,
> and that if you run that kernel with a file system and alsa compiled
> with glibc (angstrom linux) alsactl works perfectly.
> So after 5 days of digging, I found that the alsa drivers in the kernel
> are compiled with the -mabi=aapcs-linux option in gcc.
> If I add that option to CFLAGS in the alsa-lib configure script and
> compile, alsactl works perfectly!
> So I suggest to put the option
> 
> -mabi=aapcs-linux
> 
> to all the compilation of uclibc and buildroot.
> I would propose the patch, but I do not know where to put the option in
> the scripts/configuration.
> Hope that helps,
> 
> Federico Fuga
> 
> 

Yes, I can confirm that adding

CFLAGS="$(TARGET_CFLAGS) -mabi=aapcs-linux"

to alsa_utils.mk and alsa-utils.mk indeed fixes a problem for ARM (tested on ARM920T Cirrus Logic CPU)