Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, Apr 09, 2018 at 03:51:10PM +0100, Singh, Jasvinder wrote:
> 
> > -----Original Message-----
> > From: Richardson, Bruce
> > Sent: Monday, April 9, 2018 2:09 PM
> > To: Singh, Jasvinder <jasvinder.singh@intel.com>
> > Cc: dev@dpdk.org; Dumitrescu, Cristian <cristian.dumitrescu@intel.com>
> > Subject: Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8
> > 
> > On Mon, Apr 09, 2018 at 01:49:48PM +0100, Jasvinder Singh wrote:
> > > Fix build error with gcc 8.0 due to cast between function types.
> > > Fixes: 5a80bf0ae613 ("table: add cuckoo hash")
> > >
> > > Signed-off-by: Jasvinder Singh <jasvinder.singh@intel.com>
> > 
> > What's the actual error message? Why do the types not match?
> > 
> > /Bruce
>  
> Error log is captured below;
> 
>   CC rte_table_hash_cuckoo.o
> /librte_table/rte_table_hash_cuckoo.c: In function 'rte_table_hash_cuckoo_create':
> /librte_table/rte_table_hash_cuckoo.c:110:16: error: cast between incompatible
>  function types from 'rte_table_hash_op_hash' {aka 'long unsigned int (*)(void *, void *, unsigned int,  long unsigned int)'}
>  to 'uint32_t (*)(const void *, uint32_t,  uint32_t)' {aka 'unsigned int (*)(const void *, unsigned int,  unsigned int)'} [-Werror=cast-function-type]
>    .hash_func = (rte_hash_function) p->f_hash,
>                 ^
> cc1: all warnings being treated as errors
> 
Even if the compiler isn't complaining now, how can that cast work? Looking
at the error message given, it appears there are two big issues:

1. The expected function call takes 3 parameters:
	(const void *, uint32_t,  uint32_t),
   but you are giving it a function that takes 4 parameters:
	(void *, void *, unsigned int,  long unsigned int)
2. The return type expected is "unsigned int", but you are giving a
   function returning "long unsigned int". On 32-bit systems, these are
   going to be the same size, but on 64-bit, they will be different.
   Similarly for the last function argument.

Is the error message correct?

/Bruce