Re: [PATCH] WAVELAN - compile-time check for struct sizes

["John W. Linville" <linville@tuxdriver.com>]

On Wed, Feb 06, 2008 at 01:59:50PM -0800, Andrew Morton wrote:
> On Wed, 6 Feb 2008 21:47:47 +0000
> Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:

> > I assume that it's the second BUILD_BUG_ON() which is triggering?
> 
> yup.
> 
> > Given that:
> > 
> > #define MMW_SIZE        37
> > 
> > is not a multiple of sizeof(unsigned long) this is hardly surprising.
> > 
> > If structures are used to define a layout of something and must not
> > contain compiler padding, it must be packed.  Given these structures
> > contain just unsigned char, there's no concerns about >8bit loads
> > becoming less efficient.

Does a patch like this suffice?  I haven't checked whether such a
patch implies that the BUILD_BUG_ON()'s become unnecessary...

Does anyone actually have this hardware to test?

---

From: John W. Linville <linville@tuxdriver.com>
Subject: [PATCH] wavelan: mark hardware interfacing structures as packed

Signed-off-by: John W. Linville <linville@tuxdriver.com>
---
 drivers/net/wireless/wavelan.h |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/wavelan.h b/drivers/net/wireless/wavelan.h
index 27172cd..964db3e 100644
--- a/drivers/net/wireless/wavelan.h
+++ b/drivers/net/wireless/wavelan.h
@@ -100,7 +100,7 @@ struct ha_t
 	unsigned short	ha_piop1;	/* Program I/O Port 1 */
 	unsigned short	ha_pior2;	/* Program I/O Address Register Port 2 */
 	unsigned short	ha_piop2;	/* Program I/O Port 2 */
-};
+} __attribute__ ((packed));
 
 #define HA_SIZE		16
 
@@ -202,7 +202,7 @@ struct psa_t
   unsigned char	psa_conf_status;	/* [0x3C] Conf Status, bit 0=1:config*/
   unsigned char	psa_crc[2];		/* [0x3D] CRC-16 over PSA */
   unsigned char	psa_crc_status;		/* [0x3F] CRC Valid Flag */
-};
+} __attribute__ ((packed));
 
 #define	PSA_SIZE	64
 
@@ -292,7 +292,7 @@ struct mmw_t
 #define	MMW_EXT_ANT_INTERNAL	0x00	/* Internal antenna */
 #define	MMW_EXT_ANT_EXTERNAL	0x03	/* External antenna */
 #define	MMW_EXT_ANT_IQ_TEST	0x1C	/* IQ test pattern (set to 0) */
-};
+} __attribute__ ((packed));;
 
 #define	MMW_SIZE	37
 
@@ -347,7 +347,7 @@ struct mmr_t
   unsigned char	mmr_unused4[1];		/* unused */
   unsigned char	mmr_fee_data_l;		/* Read data from EEPROM (low) */
   unsigned char	mmr_fee_data_h;		/* Read data from EEPROM (high) */
-};
+} __attribute__ ((packed));
 
 #define	MMR_SIZE	36
 
-- 
1.5.3.3

-- 
John W. Linville
linville@tuxdriver.com