Re: [dpdk-dev] [PATCH 1/2] eal: detect endianness

["Qiu, Michael" <michael.qiu@intel.com>]

On 12/4/2014 8:20 PM, Thomas Monjalon wrote:
> 2014-12-04 10:28, Qiu, Michael:
>> On 12/4/2014 5:01 PM, Thomas Monjalon wrote:
>>> 2014-12-04 02:28, Qiu, Michael:
>>>> On 12/4/2014 5:26 AM, Thomas Monjalon wrote:
>>>>> There is no standard to check endianness.
>>>>> So we need to try different checks.
>>>>> Previous trials were done in testpmd (see commits
>>>>> 51f694dd40f56 and 64741f237cf29) without full success.
>>>>> This one is not guaranteed to work everywhere so it could
>>>>> evolve when exceptions are found.
>>> [...]
>>>>>  #include <stdint.h>
>>>>> +#ifdef RTE_EXEC_ENV_BSDAPP
>>>>> +#include <sys/endian.h>
>>>>> +#else
>>>>> +#include <endian.h>
>>>>> +#endif
>>>>> +
>>>>> +/*
>>>>> + * Compile-time endianness detection
>>>>> + */
>>>>> +#define RTE_BIG_ENDIAN    1
>>>>> +#define RTE_LITTLE_ENDIAN 2
>>>>> +#if defined __BYTE_ORDER
>>>>> +#if __BYTE_ORDER == __BIG_ENDIAN
>>>>> +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
>>>>> +#elif __BYTE_ORDER == __LITTLE_ENDIAN
>>>>> +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
>>>>> +#endif /* __BYTE_ORDER */
>>>>> +#elif defined __BYTE_ORDER__
>>>>> +#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
>>>>> +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
>>>>> +#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
>>>>> +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
>>>>> +#endif /* __BYTE_ORDER__ */
>>>>> +#elif defined __BIG_ENDIAN__
>>>>> +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
>>>>> +#elif defined __LITTLE_ENDIAN__
>>>>> +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
>>>>> +#endif
>>>> What do you think about :
>>>>
>>>> +/*
>>>> +  * Compile-time endianness detection
>>>> + */
>>>> +#define RTE_BIG_ENDIAN 1
>>>> +#define RTE_LITTLE_ENDIAN 2
>>>> +if defined __BYTE_ORDER__    /* Prefer gcc build-in macros */
>>>> +#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
>>>> +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
>>>> +#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
>>>> +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
>>>> +#endif /* __BYTE_ORDER__ */
>>>> +#else
>>>> +#if defined RTE_EXEC_ENV_BSDAPP
>>>> +#include <sys/endian.h>
>>>> +#else
>>>> +#include <endian.h>
>>>> +#endif
>>>> +#if defined __BYTE_ORDER
>>>> +#if __BYTE_ORDER == __BIG_ENDIAN
>>>> +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
>>>> +#elif __BYTE_ORDER == __LITTLE_ENDIAN
>>>> +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
>>>> +#endif /* __BYTE_ORDER */
>>>> +#elif defined __BIG_ENDIAN__
>>>> +#define RTE_BYTE_ORDER RTE_BIG_ENDIAN
>>>> +#elif defined __LITTLE_ENDIAN__
>>>> +#define RTE_BYTE_ORDER RTE_LITTLE_ENDIAN
>>>> +#endif
>>>> +#endif
>>> Please, could you give more explanations about your proposal?
>>> Why not always try to include endian.h?
>> I assume that if gcc can handler why we need include that file?
> Separating include on top is easier to read, and I'm not sure it won't
> be needed for __BYTE_ORDER__ with some toolchains.
>
>> Also it seems that only old version could have this issue, newer
>> versions has build in this marcos.
>>
>> So that's why I prefer  "__BYTE_ORDER__" for high priority.
> I have no problem with reversing this priority.
>
>>> Why giving high priority to __BYTE_ORDER__?
> Any other comment? May I apply with above change?

Acked-by: Michael Qiu <michael.qiu@intel.com>