Re: [Qemu-devel] [PATCH 1/7] s390x/pci: factor out endianess conversion

[Philippe Mathieu-Daudé]

On 11/09/2017 01:38 PM, Cornelia Huck wrote:
> On Tue,  7 Nov 2017 18:24:33 +0100
> Pierre Morel <address@hidden> wrote:
> 
>> There are two places where the same endianness conversion
>> is done.
>> Let's factor this out into a static function.
>>
>> Signed-off-by: Pierre Morel <address@hidden>
>> Reviewed-by: Yi Min Zhao <address@hidden>
>> ---
>>  hw/s390x/s390-pci-inst.c | 58 
>> ++++++++++++++++++++++++++----------------------
>>  1 file changed, 32 insertions(+), 26 deletions(-)
>>
>> diff --git a/hw/s390x/s390-pci-inst.c b/hw/s390x/s390-pci-inst.c
>> index 8e088f3..8fcb02d 100644
>> --- a/hw/s390x/s390-pci-inst.c
>> +++ b/hw/s390x/s390-pci-inst.c
>> @@ -314,6 +314,35 @@ out:
>>      return 0;
>>  }
>>  
>> +/**
>> + * This function swaps the data at ptr according from one
>> + * endianness to the other.
>> + * valid data in the uint64_t data field.
> 
> I'm not sure what that line is supposed to mean?
> 
>> + * @ptr: a pointer to a uint64_t data field
>> + * @len: the length of the valid data, must be 1,2,4 or 8
>> + */
>> +static int zpci_endian_swap(uint64_t *ptr, uint8_t len)
>> +{
>> +    uint64_t data = *ptr;
>> +    switch (len) {
>> +    case 1:
>> +        break;
>> +    case 2:
>> +        data = bswap16(data);
>> +        break;
>> +    case 4:
>> +        data = bswap32(data);
>> +        break;
>> +    case 8:
>> +        data = bswap64(data);
>> +        break;
>> +    default:
>> +        return -EINVAL;
>> +    }
>> +    *ptr = data;
>> +    return 0;
>> +}

This is usually care taken by memory::adjust_endianness() ...

> I was expecting more code to use a similar pattern, but it seems
> surprisingly uncommon.

Which ring a bell for latent bug?

This remind me of a similar issue on ppc:

http://lists.nongnu.org/archive/html/qemu-devel/2017-02/msg05121.html
...
http://lists.nongnu.org/archive/html/qemu-devel/2017-02/msg05666.html