Dear Przemyslaw Marczak,
In message
<cc0f558724a4d3ea3497b84601038f5f18f37a7b.1394037321.git.p.marc...@samsung.com>
you wrote:
> This patch adds support to generate UUID (Universally Unique Identifier)
> in version 4 based on RFC4122, which is randomly.
...
> +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];
> +};
This struct starts with an uint, so it requires alignment on a 32 bit
boundary (i. e. an address that is a multiple of 4).
> +void gen_rand_uuid(unsigned char *uuid_bin)
> +{
> + struct uuid *uuid = (struct uuid *)uuid_bin;
Here you cast a pointer to the (unaligned) character buffer to a
struct buffer, which requires alignment.
> + unsigned int *ptr = (unsigned int *)uuid_bin;
> + /* Set all fields randomly */
> + for (i = 0; i < sizeof(struct uuid) / sizeof(*ptr); i++)
> + *(ptr + i) = rand();
This code is dangerous - if the size of the struct should not be a
multiple of sizeof(uint), there would remain uninitialized data.
And note that it is likely that all these accesses are unaligned and
might cause exceptions.
> + /* Set V4 format */
> + uuid->time_hi_and_version &= UUID_VERSION_CLEAR_BITS;
> + uuid->time_hi_and_version |= UUID_VERSION << UUID_VERSION_SHIFT;
Potentially unaligned accesses.
Best regards,
Wolfgang Denk
--
DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: w...@denx.de
As a general rule, the freedom of any people can be judged by the
volume of their laughter.
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