Re: [alsa-devel] [PATCH v7 8/9] ALSA: add new 32-bit layout for snd_pcm_mmap_status/control

[Takashi Iwai]

On Wed, 06 Oct 2021 19:49:17 +0200,
Michael Forney wrote:
> 
> Arnd Bergmann <arnd@xxxxxxxx> wrote:
> > +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> > +typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > +typedef char __pad_after_uframe[0];
> > +#endif
> > +
> > +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> > +typedef char __pad_before_uframe[0];
> > +typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> > +#endif
> > +
> > +struct __snd_pcm_mmap_status64 {
> > +	__s32 state;			/* RO: state - SNDRV_PCM_STATE_XXXX */
> > +	__u32 pad1;			/* Needed for 64 bit alignment */
> > +	__pad_before_uframe __pad1;
> > +	snd_pcm_uframes_t hw_ptr;	/* RO: hw ptr (0...boundary-1) */
> > +	__pad_after_uframe __pad2;
> > +	struct __snd_timespec64 tstamp;	/* Timestamp */
> > +	__s32 suspended_state;		/* RO: suspended stream state */
> > +	__u32 pad3;			/* Needed for 64 bit alignment */
> > +	struct __snd_timespec64 audio_tstamp; /* sample counter or wall clock */
> > +};
> > +
> > +struct __snd_pcm_mmap_control64 {
> > +	__pad_before_uframe __pad1;
> > +	snd_pcm_uframes_t appl_ptr;	 /* RW: appl ptr (0...boundary-1) */
> > +	__pad_before_uframe __pad2;
> 
> I was looking through this header and happened to notice that this
> padding is wrong. I believe it should be __pad_after_uframe here.
> 
> I'm not sure of the implications of this typo, but I suspect it
> breaks something on 32-bit systems with 64-bit time (regardless of
> the endianness, since it changes the offset of avail_min).

Right, that's the expected breakage.  It seems that the 64bit time on
32bit arch is still rare, so we haven't heard a regression by that, so
far...

In anyway, care to send a formal fix patch?

Thanks for catching this!


Takashi