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

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 9 Apr 2018 16:28:12 +0100
Bruce Richardson <bruce.richardson@intel.com> wrote:

> 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?

Yes. the current code is working only by luck