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

[Thomas Monjalon <thomas.monjalon@6wind.com>]

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?

-- 
Thomas