[U-Boot] [PATCH 1/1] lib: uuid: alignment error in gen_rand_uuid()

[Eugeniu Rosca]

Hi Heinrich,

On Sun, Jul 14, 2019 at 11:31:50PM +0200, Heinrich Schuchardt wrote:
> Packed structures like struct uuid are not aligned. GCC 9.1 therefore
> throws an error when trying to compile gen_rand_uuid().
> 
> lib/uuid.c: In function ‘gen_rand_uuid’:
> lib/uuid.c:244:2: error: converting a packed ‘struct uuid’ pointer
> (alignment 1) to a ‘unsigned int’ pointer (alignment 4) may result in
> an unaligned pointer value [-Werror=address-of-packed-member]
>   244 |  unsigned int *ptr = (unsigned int *)&uuid;
>       |  ^~~~~~~~
> 
> Generate the uuid in a properly aligned buffer.
> 
> The byte order of a random number should not matter. Do not call
> cpu_to_be32() to change the byte order.

There is a striking resemblance between "struct uuid" [1] in U-Boot and
"struct afs_uuid" [2] in Linux, with the major difference that the
latter has never been defined as __packed.

Is there any compelling reason for the U-Boot struct to be packed?

[1] https://gitlab.denx.de/u-boot/u-boot/commit/4e4815feae4d3
    ("lib: uuid: add functions to generate UUID version 4")
 -----8<-----
 struct uuid {
 	unsigned int time_low;
 	unsigned short time_mid;
 	unsigned short time_hi_and_version;
 	unsigned char clock_seq_hi_and_reserved;
 	unsigned char clock_seq_low;
 	unsigned char node[6];
 } __packed;
 -----8<-----

[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f044c8847bb6
 -----8<-----
 struct afs_uuid {
 	__be32		time_low;			/* low part of timestamp */
 	__be16		time_mid;			/* mid part of timestamp */
 	__be16		time_hi_and_version;		/* high part of timestamp and version  */
 	__u8		clock_seq_hi_and_reserved;	/* clock seq hi and variant */
 	__u8		clock_seq_low;			/* clock seq low */
 	__u8		node[6];			/* spatially unique node ID (MAC addr) */
 };
 -----8<-----

-- 
Best Regards,
Eugeniu.