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

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

2015-03-19 02:00, Qiu, Michael:
> On 3/8/2015 2:39 AM, Thomas Monjalon wrote:
> > 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.
> 
> Hi, Thomas
> 
> Indeed what I concerned occurs, when compile target i686 in X86_64
> platform, it will call the stub function

Oh, you mean compiling for i686 and run it in x86_64 target,
so the stub for crc32c_sse42_u64 is called?

> Then, should I make a patch to fix, change the code as this one(V2)
> Another choice is you could revert V3 and merge V2.
> Or if have other solution?

It's probably saner to submit a fix you have tested with ifdef like in v2.
Thanks