Re: [Qemu-devel] [PATCH v7 2/7] tests: Add virtio device initialization

[Stefan Hajnoczi]

On Fri, Aug 29, 2014 at 12:40:43PM +0200, Marc Marí wrote:
> +static uint64_t qvirtio_pci_config_readq(QVirtioDevice *d, void *addr)
> +{
> +    QVirtioPCIDevice *dev = (QVirtioPCIDevice *)d;
> +    int i;
> +    union {
> +        uint8_t bytes[8];
> +        uint64_t u64;
> +    } quad;
> +
> +    if (qtest_big_endian()) {
> +        for (i = 0; i < 8; ++i) {
> +            quad.bytes[7-i] = qpci_io_readb(dev->pdev, addr + i);
> +        }
> +    } else {
> +        for (i = 0; i < 8; ++i) {
> +            quad.bytes[i] = qpci_io_readb(dev->pdev, addr + i);
> +        }
> +    }
> +
> +    return quad.u64;
> +}

This assumes that the host is little-endian.  The host could be
big-endian!

qvirtio_pci_config_readq() needs to return a 64-bit value in host CPU
endianness.  So the logic should be:

for (i = 0; i < 8; ++i) {
    quad.bytes[i] = qpci_io_readb(dev->pdev, addr + i);
}
if (qtest_big_endian() != qtest_host_endian()) {
    quad.u64 = bswap64(quad.u64);
}
return quard.u64;

Stefan

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