Re: [Qemu-devel] [PATCH] qtest: add read/write accessors with a specific endianness

[Cédric Le Goater]

On 10/05/2016 04:20 PM, Peter Maydell wrote:
> On 5 October 2016 at 07:00, Cédric Le Goater <address@hidden> wrote:
>> On 10/05/2016 03:53 PM, Peter Maydell wrote:
>>> Which tswap? Last time I worked through the stack of
>>> what happens I thought that we had the right set of
>>> swaps in the right places.
>>
>> The one I am talking about are under qtest_process_command(),
>> see below.
> 
> Those are correct and required, and they do not change
> the overall behaviour of the system depending on the host
> endianness. (They convert 32-bit values to "bag of
> bytes in guest order" which is what the cpu_physical_memory_*
> functions want.)
> 
> https://lists.gnu.org/archive/html/qemu-arm/2016-07/msg00037.html
> is the explanation from last time around, I think.
> 
> If your test is giving different answers on different
> host endiannesses, it is presumably because it is
> incorrectly issuing different readl/etc commands
> in the two cases.

OK. I think my brain is starting to see things from the right 
angle.

Let's try that : my test is simulating a Little Endian CPU which
is writing a Big Endian value, so it *always* needs to bswap() 
that value. cpu_to_be32 is incorrect as it implies the endianness
of the host which can be wrong (when running BE).

The qtest layer is a just fixing layer.

Thanks,
C.