scsi: pmcraid: fix 'ioarcb' alignment warning

Commit Message

Arnd Bergmann Feb. 1, 2021, 4:59 p.m. UTC

From: Arnd Bergmann <[e-mail]>

Building with 'make W=1' enables -Wpacked-not-aligned, and this
warns about pmcraid because of incompatible alignment constraints for
pmcraid_passthrough_ioctl_buffer:

drivers/scsi/pmcraid.h:1044:1: warning: alignment 1 of 'struct pmcraid_passthrough_ioctl_buffer' is less than 32 [-Wpacked-not-aligned]
 1044 | } __attribute__ ((packed));
      | ^
drivers/scsi/pmcraid.h:1041:24: warning: 'ioarcb' offset 16 in 'struct pmcraid_passthrough_ioctl_buffer' isn't aligned to 32 [-Wpacked-not-aligned]
 1041 |  struct pmcraid_ioarcb ioarcb;

The inner structure is documented as having 32 byte alignment here,
but is starts at a 16 byte offset in the outer structure, so it's never
actually aligned, as the outer structure is also marked 'packed'.

Lee Jones point this out as one of the last files that need to be changed
before the warning can be enabled by default.

Change the annotations in a way that avoids the warning but leaves the
layout unchanged, by removing the packing on the inner structure and
adding it to the outer one. The one-byte request_buffer[] array should
have been a flexible array member here, which is how I change it to
avoid extra padding from the alignment attribute.

Cc: Lee Jones <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>
---
 drivers/scsi/pmcraid.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

Lee Jones Feb. 2, 2021, 8:17 a.m. UTC | #1

On Mon, 01 Feb 2021, Arnd Bergmann wrote:

> From: Arnd Bergmann <[e-mail]>
> 
> Building with 'make W=1' enables -Wpacked-not-aligned, and this
> warns about pmcraid because of incompatible alignment constraints for
> pmcraid_passthrough_ioctl_buffer:
> 
> drivers/scsi/pmcraid.h:1044:1: warning: alignment 1 of 'struct pmcraid_passthrough_ioctl_buffer' is less than 32 [-Wpacked-not-aligned]
>  1044 | } __attribute__ ((packed));
>       | ^
> drivers/scsi/pmcraid.h:1041:24: warning: 'ioarcb' offset 16 in 'struct pmcraid_passthrough_ioctl_buffer' isn't aligned to 32 [-Wpacked-not-aligned]
>  1041 |  struct pmcraid_ioarcb ioarcb;
> 
> The inner structure is documented as having 32 byte alignment here,
> but is starts at a 16 byte offset in the outer structure, so it's never
> actually aligned, as the outer structure is also marked 'packed'.
> 
> Lee Jones point this out as one of the last files that need to be changed
> before the warning can be enabled by default.
> 
> Change the annotations in a way that avoids the warning but leaves the
> layout unchanged, by removing the packing on the inner structure and
> adding it to the outer one. The one-byte request_buffer[] array should
> have been a flexible array member here, which is how I change it to
> avoid extra padding from the alignment attribute.

Looks good to me.

Reviewed-by: Lee Jones <[e-mail]>

Patch

diff --git a/drivers/scsi/pmcraid.h b/drivers/scsi/pmcraid.h
index 15c962108075..6d36debde18e 100644
--- a/drivers/scsi/pmcraid.h
+++ b/drivers/scsi/pmcraid.h
@@ -244,7 +244,7 @@  struct pmcraid_ioarcb {
 	__u8  hrrq_id;
 	__u8  cdb[PMCRAID_MAX_CDB_LEN];
 	struct pmcraid_ioarcb_add_data add_data;
-} __attribute__((packed, aligned(PMCRAID_IOARCB_ALIGNMENT)));
+};
 
 /* well known resource handle values */
 #define PMCRAID_IOA_RES_HANDLE        0xffffffff
@@ -1040,8 +1040,8 @@  struct pmcraid_passthrough_ioctl_buffer {
 	struct pmcraid_ioctl_header ioctl_header;
 	struct pmcraid_ioarcb ioarcb;
 	struct pmcraid_ioasa  ioasa;
-	u8  request_buffer[1];
-} __attribute__ ((packed));
+	u8  request_buffer[];
+} __attribute__ ((packed, aligned(PMCRAID_IOARCB_ALIGNMENT)));
 
 /*
  * keys to differentiate between driver handled IOCTLs and passthrough