On 7/15/19 10:42 AM, Eugeniu Rosca wrote:
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?
Thanks for your analysis.
struct uuid is only used in lib/uuid.c inside gen_rand_uuid(). Hence there is no need make this structure packed. We should still remove the superfluous call to cpu_to_be32().
Best regards
Heinrich
[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/?i... -----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<-----