For the moment, I am focusing on the frontend ioctl problem
According to the fops:
static const struct file_operations dvb_frontend_fops = {
.owner = THIS_MODULE,
.unlocked_ioctl = dvb_generic_ioctl,
.poll = dvb_frontend_poll,
.open = dvb_frontend_open,
.release = dvb_frontend_release,
.llseek = noop_llseek,
};
There is no support for compact_ioctl, so it must be added
2017-11-02 19:52 GMT+01:00 Alan Cox <gnomes@xxxxxxxxxxxxxxxxxxx>:
> On Thu, 2 Nov 2017 12:16:39 +0100
> Menion <menion@xxxxxxxxx> wrote:
>
>> Hi all
>> I am investigating for Armbian, the feasability of running 32bit
>> userland on single board computers based on arm64 SoC, where only 64
>> bit kernel is available, for reducing the memory footprint.
>> I have discovered that there is a flaw in the DVB frontend ioctl (at
>> least) that prevents to do so.
>> in frontend.h the biggest problem is:
>>
>> struct dtv_properties {
>> __u32 num;
>> struct dtv_property *props;
>> };
>>
>> The master userland-kernel ioctl structure is based on an array set by
>> pointer, so the 32bit userland will allocate 32bit pointer (and the
>> resulting structure size) while the 64bit kernel will expect the 64bit
>> pointers
>
> And in some cases the pointer might end up aligned to the next 64bit
> boundary.
>
>> The void *reserved2 field will also give problem when crossing the
>> 32-64bits boundaries
>> As today the endire dvb linux infrastructure can only work in 32-32
>> and 64-64 bit mode
>
> If this isn't handled by the existing media compat_ioctl support then you
> can send patches to use compat_ioctl handlers to fix this.
>
> Alan
