Jan Kiszka wrote:
Jan Kiszka wrote:
Wolfgang Grandegger wrote:
Jan Kiszka wrote:
Oliver Hartkopp wrote:
When you're touching anything inside your API, have you ever thought to add

__attribute__ ((aligned(8)))

to the data[8] element of the struct can_frame?

This would enable you to make 64 bit compares directly in the data
section of the can_frame ...

typedef __u32 canid_t;

struct can_frame {
    canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
    __u8    can_dlc; /* data length code: 0 .. 8 */
    __u8    data[8] __attribute__ ((aligned(8)));
[Swallowing down my well-known opinion on typeof(can_dlc) :)]

Yes, this should be done, already for the more urging sake of
unambiguous layout of the structure across the kernel/user space border.
Is this not already the case? At least the size of struct can_frame is 16 bytes.
On all target archs? With all supported compilers? Better make it explicit.

gcc -Os is such an example, toasting the assumed can_frame layout by
moving that 3-byte hole *after* data.

Ah, oh, this is always the case, not only with "-0s", as my tests show. But the size of the structure is always 16.

So this was an urging ABI bug, and I applied the alignment to both
stable and trunk Xenomai SVNs. Thanks to Oliver for insisting on this!



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