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From: Richard Henderson <rth@twiddle.net>
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Date: Wed, 10 Aug 2016 16:25:56 +0530
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Subject: Re: [Qemu-devel] [PATCH v3 1/9] util: Add UUID API
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To: Fam Zheng <famz@redhat.com>, qemu-devel@nongnu.org
Cc: kwolf@redhat.com, qemu-block@nongnu.org, sw@weilnetz.de, jcody@redhat.com, mdroth@linux.vnet.ibm.com, armbru@redhat.com, pbonzini@redhat.com, mreitz@redhat.com

On 08/09/2016 12:19 PM, Fam Zheng wrote:
> +/* Version 4 UUID (pseudo random numbers), RFC4122 4.4. */
> +
> +typedef struct {
> +    unsigned char data[16];
> +} QemuUUID;
...
> +void qemu_uuid_generate(QemuUUID *uuid)
> +{
> +    int i;
> +    uint32_t *out = (uint32_t *)&uuid->data[0];

You can't do this cast without adding alignment on the QemuUUID structure.

> +    for (i = 0; i < 4; ++i) {
> +        out[i] = g_random_int();
> +    }

But if there's no other need for uint32_t access to QemuUUID, you could either

(1) write into a local uint32_t[4] array and memcpy over, or
(2) use stl_he_p from qemu/bswap.h, which will handle the unaligned store.


r~