Re: [Qemu-devel] [PATCH 1/6] qtest: add test framework

[Stefan Hajnoczi]

On Mon, Jan 16, 2012 at 5:08 PM, Anthony Liguori <address@hidden> wrote:
> On 01/16/2012 10:59 AM, Stefan Hajnoczi wrote:
>>
>> On Fri, Jan 13, 2012 at 6:32 PM, Anthony Liguori<address@hidden>
>>  wrote:
>>>
>>> +    if (strcmp(words[0], "outb") == 0 ||
>>> +        strcmp(words[0], "outw") == 0 ||
>>> +        strcmp(words[0], "outl") == 0) {
>>> +        uint16_t addr;
>>> +        uint32_t value;
>>> +
>>> +        g_assert(words[1]&&  words[2]);
>>> +        addr = strtol(words[1], NULL, 0);
>>> +        value = strtol(words[2], NULL, 0);
>>> +
>>> +        if (words[0][3] == 'b') {
>>> +            cpu_outb(addr, value);
>>> +        } else if (words[0][3] == 'w') {
>>> +            cpu_outw(addr, value);
>>> +        } else if (words[0][3] == 'l') {
>>> +            cpu_outl(addr, value);
>>> +        }
>>> +        qtest_send_prefix(chr);
>>> +        qtest_send(chr, "OK\n");
>>> +    } else if (strcmp(words[0], "inb") == 0 ||
>>> +        strcmp(words[0], "inw") == 0 ||
>>> +        strcmp(words[0], "inl") == 0) {
>>> +        uint16_t addr;
>>> +        uint32_t value = -1U;
>>> +
>>> +        g_assert(words[1]);
>>> +        addr = strtol(words[1], NULL, 0);
>>> +
>>> +        if (words[0][2] == 'b') {
>>> +            value = cpu_inb(addr);
>>> +        } else if (words[0][2] == 'w') {
>>> +            value = cpu_inw(addr);
>>> +        } else if (words[0][2] == 'l') {
>>> +            value = cpu_inl(addr);
>>> +        }
>>> +        qtest_send_prefix(chr);
>>> +        qtest_send(chr, "OK 0x%04x\n", value);
>>
>>
>> Endianness is a little weird here.  memory.c will byteswap if target
>> and device endianness differ.
>>
>> Imagine the case where we're on an x86 host, running a ppc guest,
>> reading from PCI configuration space (little-endian).
>
>
> These functions expect to get host native endian.  The qtest wire protocol
> is a string (which has no endianness) and converts it to host native endian.

The cpu_inl() return value is not host native endian.  We perform a
byteswap if the memory region endianness is different from the target
endianness.  For example, big-endian target and little-endian device
means we byteswap.  Little-endian target and little-endian device
means we do not byteswap.

Running the same test binary against qemu-system-x86_64 and
qemu-system-$be_arch results in 0 and 1 byteswaps, respectively.  Both
can't be right.

>>  Since ppc
>> (target endian) is big-endian and the device is little-endian the
>> value read/written will be byteswapped.  However, our qtest runs on
>> the host and therefore we don't want that automatic swap (or we need
>> to neutralize it by performing another byteswap on top).
>
>
> ppc wouldn't use outb/inb.  It would do mmio to the PIO region which would
> send it through the host controller (which would do byte swapping as
> necessary).
>
> So a qtest test case would have to do little endian MMIO to interact with
> the PCI bus.

Maybe ppc is a bad example, but are there other targets where in/out is used?

Stefan