Re: [dpdk-dev] [PATCH 1/3 v2] librte_hash: Fix unsupported instruction `crc32' in i686 platform

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

2015-03-06 01:39, Qiu, Michael:
> On 3/6/2015 1:11 AM, Thomas Monjalon wrote:
> > 2015-03-06 00:55, Michael Qiu:
> >> CC rte_hash.o
> >> Error: unsupported instruction `crc32'
> >>
> >> The root cause is that i686 platform does not support 'crc32q'
> >> Need make it only available in x86_64 platform
> >>
> >> Signed-off-by: Michael Qiu <michael.qiu@intel.com>
> >> ---
> >> v2 --> v1:
> >>          Make crc32 instruction only works in X86 platform
> >>  lib/librte_hash/rte_hash_crc.h | 12 ++++++++++++
> >>  1 file changed, 12 insertions(+)
> >>
> >> diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
> >> index d28bb2a..c0a789e 100644
> >> --- a/lib/librte_hash/rte_hash_crc.h
> >> +++ b/lib/librte_hash/rte_hash_crc.h
> >> @@ -364,6 +364,7 @@ crc32c_2words(uint64_t data, uint32_t init_val)
> >>  	return crc;
> >>  }
> >>  
> >> +#if defined RTE_ARCH_I686 || defined RTE_ARCH_X86_64
> >>  static inline uint32_t
> >>  crc32c_sse42_u32(uint32_t data, uint32_t init_val)
> >>  {
> >> @@ -373,7 +374,9 @@ crc32c_sse42_u32(uint32_t data, uint32_t init_val)
> >>  			: [data] "rm" (data));
> >>  	return init_val;
> >>  }
> >> +#endif
> > 
> > Wouldn't it be more elegant to define a stub which returns 0 in #else
> > in order to remove #ifdef below?
> > Not sure, matter of taste.
> 
> It may be not a good idea, see rte_hash_crc_8byte(), if no crc32
> support, it will use crc32c_2words(), if we define a stub which returns
> 0 in #else, then we need always check the return value whether it is
> none-zero otherwise need fallback.

I don't think so.
The stub won't never been called because they are protected by the cpuflag
condition.