Re: [PATCH v3 03/33] staging: rtl8192e: Mark unaligned memcpy()

Mateusz Kulikowski
2015-05-14T20:29:44Z

On 13.05.2015 10:22, Dan Carpenter wrote:
> On Tue, May 12, 2015 at 10:00:13PM +0200, Mateusz Kulikowski wrote:
>> On 11.05.2015 10:26, Dan Carpenter wrote:
(...)
>>>
>>> Which part isn't aligned? I think they both are.
>>>
>> struct rtllib_rxb *prxb = prxbIndicateArray[j];
>>
>> struct rtllib_rxb {
>> u8 nr_subframes;
>> struct sk_buff *subframes[MAX_SUBFRAME_COUNT == 64];
>> u8 dst[ETH_ALEN]; // here
>> u8 src[ETH_ALEN]; // here
>> } __packed;
>>
>> Either I forgot alignment / packing rules or this fields are never aligned "by design".
>
> You must have forgotten something... Everything after the pointer is
> going to be aligned sizeof(void *).

That would be true, if structure was not __packed:

$ pahole drivers/staging/rtl8192e/rtllib.ko -C rtllib_rxb
struct rtllib_rxb {
u8 nr_subframes; /* 0 1 */
struct sk_buff * subframes[64]; /* 1 256 */
/* --- cacheline 4 boundary (256 bytes) was 1 bytes ago --- */
u8 dst[6]; /* 257 6 */
u8 src[6]; /* 263 6 */

/* size: 269, cachelines: 5, members: 4 */
/* last cacheline: 13 bytes */
};

Am I right?

Regards,
Mateusz