ALSA: core: fix 64-bit SNDRV_PCM_IOCTL_STATUS ABI breakage

Commit 4eeaaeaea (ALSA: core: add hooks for audio timestamps) added the new audio_tstamp field to struct snd_pcm_status. However, struct timespec requires 64-bit alignment, so the 64-bit compiler would insert 32 bits of padding before this field, which broke SNDRV_PCM_IOCTL_STATUS with error messages like this:

kernel: unknown ioctl = 0x80984120

To solve this, insert the padding explicitly so that it can be taken into account when calculating the ABI structure size.

Signed-off-by Clemens Ladisch <[email protected]>

---
 include/uapi/sound/asound.h |    3 ++-
 sound/core/pcm_compat.c     |    3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

include/uapi/sound/asound.h +2 -1

@@ -408,8 +408,9 @@ struct snd_pcm_status {
 	snd_pcm_uframes_t avail_max;	/* max frames available on hw since last status */
 	snd_pcm_uframes_t overrange;	/* count of ADC (capture) overrange detections from last status */
 	snd_pcm_state_t suspended_state; /* suspended stream state */
+	__u32 reserved_alignment;	/* must be filled with zero */
 	struct timespec audio_tstamp;	/* from sample counter or wall clock */
-	unsigned char reserved[60-sizeof(struct timespec)]; /* must be filled with zero */
+	unsigned char reserved[56-sizeof(struct timespec)]; /* must be filled with zero */
 };
 
 struct snd_pcm_mmap_status {

sound/core/pcm_compat.c +2 -1

@@ -190,8 +190,9 @@ struct snd_pcm_status32 {
 	u32 avail_max;
 	u32 overrange;
 	s32 suspended_state;
+	u32 reserved_alignment;
 	struct compat_timespec audio_tstamp;
-	unsigned char reserved[60-sizeof(struct compat_timespec)];
+	unsigned char reserved[56-sizeof(struct compat_timespec)];
 } __attribute__((packed));
 
 

Quoted 11 lines · Clemens Ladisch

Commit 4eeaaeaea (ALSA: core: add hooks for audio timestamps) added the new audio_tstamp field to struct snd_pcm_status. However, struct timespec requires 64-bit alignment, so the 64-bit compiler would insert 32 bits of padding before this field, which broke SNDRV_PCM_IOCTL_STATUS with error messages like this:

kernel: unknown ioctl = 0x80984120

To solve this, insert the padding explicitly so that it can be taken into account when calculating the ABI structure size.

Quoted 1 line

Signed-off-by Clemens Ladisch <[email protected]>

Oops, that's bad. Thanks for catching this.
I applied it now to for-next branch.

Could you fix alsa-lib code as well?

Quoted 12 lines · Takashi Iwai

Quoted 11 lines · Clemens Ladisch

Commit 4eeaaeaea (ALSA: core: add hooks for audio timestamps) added the new audio_tstamp field to struct snd_pcm_status. However, struct timespec requires 64-bit alignment, so the 64-bit compiler would insert 32 bits of padding before this field, which broke SNDRV_PCM_IOCTL_STATUS with error messages like this:

kernel: unknown ioctl = 0x80984120

To solve this, insert the padding explicitly so that it can be taken into account when calculating the ABI structure size.

Quoted 6 lines

Quoted 1 line

Signed-off-by Clemens Ladisch <[email protected]>

Oops, that's bad. Thanks for catching this.
I applied it now to for-next branch.

Could you fix alsa-lib code as well?

Oops; done.