[PATCH] table: fix build error with gcc 8

[PATCH] table: fix build error with gcc 8

[Jasvinder Singh]

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>
---
 lib/librte_table/rte_table_hash_cuckoo.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/librte_table/rte_table_hash_cuckoo.c b/lib/librte_table/rte_table_hash_cuckoo.c
index dcb4fe9..f7eae27 100644
--- a/lib/librte_table/rte_table_hash_cuckoo.c
+++ b/lib/librte_table/rte_table_hash_cuckoo.c
@@ -103,11 +103,13 @@ rte_table_hash_cuckoo_create(void *params,
 		return NULL;
 	}
 
+	void *hash_func = p->f_hash;
+
 	/* Create cuckoo hash table */
 	struct rte_hash_parameters hash_cuckoo_params = {
 		.entries = p->n_keys,
 		.key_len = p->key_size,
-		.hash_func = (rte_hash_function)(p->f_hash),
+		.hash_func = (rte_hash_function) hash_func,
 		.hash_func_init_val = p->seed,
 		.socket_id = socket_id,
 		.name = p->name
-- 
2.9.3

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

[Dumitrescu, Cristian]

> -----Original Message-----
> From: Singh, Jasvinder
> Sent: Monday, April 9, 2018 1:50 PM
> To: dev@dpdk.org
> Cc: Dumitrescu, Cristian <cristian.dumitrescu@intel.com>
> Subject: [PATCH] table: fix build error with gcc 8
> 
> 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>
> ---
>  lib/librte_table/rte_table_hash_cuckoo.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_table/rte_table_hash_cuckoo.c
> b/lib/librte_table/rte_table_hash_cuckoo.c
> index dcb4fe9..f7eae27 100644
> --- a/lib/librte_table/rte_table_hash_cuckoo.c
> +++ b/lib/librte_table/rte_table_hash_cuckoo.c
> @@ -103,11 +103,13 @@ rte_table_hash_cuckoo_create(void *params,
>  		return NULL;
>  	}
> 
> +	void *hash_func = p->f_hash;
> +
>  	/* Create cuckoo hash table */
>  	struct rte_hash_parameters hash_cuckoo_params = {
>  		.entries = p->n_keys,
>  		.key_len = p->key_size,
> -		.hash_func = (rte_hash_function)(p->f_hash),
> +		.hash_func = (rte_hash_function) hash_func,
>  		.hash_func_init_val = p->seed,
>  		.socket_id = socket_id,
>  		.name = p->name
> --
> 2.9.3

Acked-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>

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

[Bruce Richardson]

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

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

[Singh, Jasvinder]

> -----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

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

[Stephen Hemminger]

On Mon,  9 Apr 2018 13:49:48 +0100
Jasvinder Singh <jasvinder.singh@intel.com> 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>
> ---
>  lib/librte_table/rte_table_hash_cuckoo.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_table/rte_table_hash_cuckoo.c b/lib/librte_table/rte_table_hash_cuckoo.c
> index dcb4fe9..f7eae27 100644
> --- a/lib/librte_table/rte_table_hash_cuckoo.c
> +++ b/lib/librte_table/rte_table_hash_cuckoo.c
> @@ -103,11 +103,13 @@ rte_table_hash_cuckoo_create(void *params,
>  		return NULL;
>  	}
>  
> +	void *hash_func = p->f_hash;
> +
>  	/* Create cuckoo hash table */
>  	struct rte_hash_parameters hash_cuckoo_params = {
>  		.entries = p->n_keys,
>  		.key_len = p->key_size,
> -		.hash_func = (rte_hash_function)(p->f_hash),
> +		.hash_func = (rte_hash_function) hash_func,
>  		.hash_func_init_val = p->seed,
>  		.socket_id = socket_id,
>  		.name = p->name

This is just tricking the compiler into not complaining.
I would really rather see the two hash functions made the same.

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

[Bruce Richardson]

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

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

[Dumitrescu, Cristian]

> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Monday, April 9, 2018 4:10 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,  9 Apr 2018 13:49:48 +0100
> Jasvinder Singh <jasvinder.singh@intel.com> 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>
> > ---
> >  lib/librte_table/rte_table_hash_cuckoo.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/librte_table/rte_table_hash_cuckoo.c
> b/lib/librte_table/rte_table_hash_cuckoo.c
> > index dcb4fe9..f7eae27 100644
> > --- a/lib/librte_table/rte_table_hash_cuckoo.c
> > +++ b/lib/librte_table/rte_table_hash_cuckoo.c
> > @@ -103,11 +103,13 @@ rte_table_hash_cuckoo_create(void *params,
> >  		return NULL;
> >  	}
> >
> > +	void *hash_func = p->f_hash;
> > +
> >  	/* Create cuckoo hash table */
> >  	struct rte_hash_parameters hash_cuckoo_params = {
> >  		.entries = p->n_keys,
> >  		.key_len = p->key_size,
> > -		.hash_func = (rte_hash_function)(p->f_hash),
> > +		.hash_func = (rte_hash_function) hash_func,
> >  		.hash_func_init_val = p->seed,
> >  		.socket_id = socket_id,
> >  		.name = p->name
> 
> This is just tricking the compiler into not complaining.
> I would really rather see the two hash functions made the same.

(Adding Bruce as well to consolidate all conversations in a single thread.)

What we want to do here is be able to use the librte_hash under the same API as the several hash table flavors implemented in librte_table.

Both of these libraries allow configuring the hash function per each hash table instance. Problem is: hash function in librte_hash has only 3 parameters (no key mask), while hash function in librte_table has 4 parameters (includes key mask). The key mask helps a lot for practical protocol implementations by avoiding key copy & pre-process on lookup.

So then: how to plug in librte_hash under the same API as the suite of hash tables in librte_table? We don't want to re-implement cuckoo hash from librte_hash, we simply want to invoke it as a low-level primitive, similarly to how the LPM and ACL tables are plugged into librte_table.

Solution is: as an exception, pass a 3-parameter hash function to cuckoo hash flavor under the librte_table. Maybe this should be documented better. This currently triggers a build warning with gcc 8, which is easy to fix, hence this trivial patch.

Ideally, for every 3-parameter hash function, I would like to generate the corresponding 4-parameter hash function on-the-fly, but unfortunately this is not what C language can do.

Of course, IMO the best solution is to add key mask support to librte_hash.

Regards,
Cristian

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

[Van Haaren, Harry]

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Dumitrescu, Cristian
> Sent: Monday, April 9, 2018 4:59 PM
> To: Stephen Hemminger <stephen@networkplumber.org>; Singh, Jasvinder
> <jasvinder.singh@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8
> 
> 
> 
> > -----Original Message-----
> > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > Sent: Monday, April 9, 2018 4:10 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,  9 Apr 2018 13:49:48 +0100
> > Jasvinder Singh <jasvinder.singh@intel.com> 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>
> > > ---
> > >  lib/librte_table/rte_table_hash_cuckoo.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/lib/librte_table/rte_table_hash_cuckoo.c
> > b/lib/librte_table/rte_table_hash_cuckoo.c
> > > index dcb4fe9..f7eae27 100644
> > > --- a/lib/librte_table/rte_table_hash_cuckoo.c
> > > +++ b/lib/librte_table/rte_table_hash_cuckoo.c
> > > @@ -103,11 +103,13 @@ rte_table_hash_cuckoo_create(void *params,
> > >  		return NULL;
> > >  	}
> > >
> > > +	void *hash_func = p->f_hash;
> > > +
> > >  	/* Create cuckoo hash table */
> > >  	struct rte_hash_parameters hash_cuckoo_params = {
> > >  		.entries = p->n_keys,
> > >  		.key_len = p->key_size,
> > > -		.hash_func = (rte_hash_function)(p->f_hash),
> > > +		.hash_func = (rte_hash_function) hash_func,
> > >  		.hash_func_init_val = p->seed,
> > >  		.socket_id = socket_id,
> > >  		.name = p->name
> >
> > This is just tricking the compiler into not complaining.
> > I would really rather see the two hash functions made the same.
> 
> (Adding Bruce as well to consolidate all conversations in a single thread.)
> 
> What we want to do here is be able to use the librte_hash under the same API
> as the several hash table flavors implemented in librte_table.
> 
> Both of these libraries allow configuring the hash function per each hash
> table instance. Problem is: hash function in librte_hash has only 3 parameters
> (no key mask), while hash function in librte_table has 4 parameters (includes
> key mask). The key mask helps a lot for practical protocol implementations by
> avoiding key copy & pre-process on lookup.
> 
> So then: how to plug in librte_hash under the same API as the suite of hash
> tables in librte_table? We don't want to re-implement cuckoo hash from
> librte_hash, we simply want to invoke it as a low-level primitive, similarly
> to how the LPM and ACL tables are plugged into librte_table.
> 
> Solution is: as an exception, pass a 3-parameter hash function to cuckoo hash
> flavor under the librte_table. Maybe this should be documented better. This
> currently triggers a build warning with gcc 8, which is easy to fix, hence
> this trivial patch.
> 
> Ideally, for every 3-parameter hash function, I would like to generate the
> corresponding 4-parameter hash function on-the-fly, but unfortunately this is
> not what C language can do.
> 
> Of course, IMO the best solution is to add key mask support to librte_hash.


Looking at the previous discussion I see the following as a possible solution;

Given the current code looks broken it should be fixed in this release.
Given the actual code fix is an API / ABI break (depending on solution) it cannot be merged official in this release.
We have a NEXT_ABI macro - it allows us to break API/ABI conditionally at compile time.

With the above 3 points, I think the best solution is to correctly fix the problem that GCC 8 is identifying, and putting that new API inside the NEXT_ macros.

In this case, we can preserve backwards (buggy) behavior if required, and provide correct (but API/ABI breaking) code as well. This is a tough decision - particularly for distros - what do they package?

Given the current code, I don't see a better solution - but I hope I'm wrong :)

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

[Stephen Hemminger]

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

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

[Ferruh Yigit]

On 4/9/2018 5:38 PM, Van Haaren, Harry wrote:
>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Dumitrescu, Cristian
>> Sent: Monday, April 9, 2018 4:59 PM
>> To: Stephen Hemminger <stephen@networkplumber.org>; Singh, Jasvinder
>> <jasvinder.singh@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>
>> Cc: dev@dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8
>>
>>
>>
>>> -----Original Message-----
>>> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
>>> Sent: Monday, April 9, 2018 4:10 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,  9 Apr 2018 13:49:48 +0100
>>> Jasvinder Singh <jasvinder.singh@intel.com> 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>
>>>> ---
>>>>  lib/librte_table/rte_table_hash_cuckoo.c | 4 +++-
>>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/lib/librte_table/rte_table_hash_cuckoo.c
>>> b/lib/librte_table/rte_table_hash_cuckoo.c
>>>> index dcb4fe9..f7eae27 100644
>>>> --- a/lib/librte_table/rte_table_hash_cuckoo.c
>>>> +++ b/lib/librte_table/rte_table_hash_cuckoo.c
>>>> @@ -103,11 +103,13 @@ rte_table_hash_cuckoo_create(void *params,
>>>>  		return NULL;
>>>>  	}
>>>>
>>>> +	void *hash_func = p->f_hash;
>>>> +
>>>>  	/* Create cuckoo hash table */
>>>>  	struct rte_hash_parameters hash_cuckoo_params = {
>>>>  		.entries = p->n_keys,
>>>>  		.key_len = p->key_size,
>>>> -		.hash_func = (rte_hash_function)(p->f_hash),
>>>> +		.hash_func = (rte_hash_function) hash_func,
>>>>  		.hash_func_init_val = p->seed,
>>>>  		.socket_id = socket_id,
>>>>  		.name = p->name
>>>
>>> This is just tricking the compiler into not complaining.
>>> I would really rather see the two hash functions made the same.
>>
>> (Adding Bruce as well to consolidate all conversations in a single thread.)
>>
>> What we want to do here is be able to use the librte_hash under the same API
>> as the several hash table flavors implemented in librte_table.
>>
>> Both of these libraries allow configuring the hash function per each hash
>> table instance. Problem is: hash function in librte_hash has only 3 parameters
>> (no key mask), while hash function in librte_table has 4 parameters (includes
>> key mask). The key mask helps a lot for practical protocol implementations by
>> avoiding key copy & pre-process on lookup.
>>
>> So then: how to plug in librte_hash under the same API as the suite of hash
>> tables in librte_table? We don't want to re-implement cuckoo hash from
>> librte_hash, we simply want to invoke it as a low-level primitive, similarly
>> to how the LPM and ACL tables are plugged into librte_table.
>>
>> Solution is: as an exception, pass a 3-parameter hash function to cuckoo hash
>> flavor under the librte_table. Maybe this should be documented better. This
>> currently triggers a build warning with gcc 8, which is easy to fix, hence
>> this trivial patch.
>>
>> Ideally, for every 3-parameter hash function, I would like to generate the
>> corresponding 4-parameter hash function on-the-fly, but unfortunately this is
>> not what C language can do.
>>
>> Of course, IMO the best solution is to add key mask support to librte_hash.
> 
> 
> Looking at the previous discussion I see the following as a possible solution;
> 
> Given the current code looks broken it should be fixed in this release.
> Given the actual code fix is an API / ABI break (depending on solution) it cannot be merged official in this release.
> We have a NEXT_ABI macro - it allows us to break API/ABI conditionally at compile time.
> 
> With the above 3 points, I think the best solution is to correctly fix the problem that GCC 8 is identifying, and putting that new API inside the NEXT_ macros.
> 
> In this case, we can preserve backwards (buggy) behavior if required, and provide correct (but API/ABI breaking) code as well. This is a tough decision - particularly for distros - what do they package?

+1 to use RTE_NEXT_ABI and deliver fixed code, and agree this is kind of pushing
decision to distros.

> 
> Given the current code, I don't see a better solution - but I hope I'm wrong :)
> 

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

[Dumitrescu, Cristian]

> -----Original Message-----
> From: Van Haaren, Harry
> Sent: Monday, April 9, 2018 5:38 PM
> To: Dumitrescu, Cristian <cristian.dumitrescu@intel.com>; Stephen
> Hemminger <stephen@networkplumber.org>; Singh, Jasvinder
> <jasvinder.singh@intel.com>; Richardson, Bruce
> <bruce.richardson@intel.com>
> Cc: dev@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH] table: fix build error with gcc 8
> 
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Dumitrescu,
> Cristian
> > Sent: Monday, April 9, 2018 4:59 PM
> > To: Stephen Hemminger <stephen@networkplumber.org>; Singh,
> Jasvinder
> > <jasvinder.singh@intel.com>; Richardson, Bruce
> <bruce.richardson@intel.com>
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8
> >
> >
> >
> > > -----Original Message-----
> > > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > > Sent: Monday, April 9, 2018 4:10 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,  9 Apr 2018 13:49:48 +0100
> > > Jasvinder Singh <jasvinder.singh@intel.com> 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>
> > > > ---
> > > >  lib/librte_table/rte_table_hash_cuckoo.c | 4 +++-
> > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/lib/librte_table/rte_table_hash_cuckoo.c
> > > b/lib/librte_table/rte_table_hash_cuckoo.c
> > > > index dcb4fe9..f7eae27 100644
> > > > --- a/lib/librte_table/rte_table_hash_cuckoo.c
> > > > +++ b/lib/librte_table/rte_table_hash_cuckoo.c
> > > > @@ -103,11 +103,13 @@ rte_table_hash_cuckoo_create(void
> *params,
> > > >  		return NULL;
> > > >  	}
> > > >
> > > > +	void *hash_func = p->f_hash;
> > > > +
> > > >  	/* Create cuckoo hash table */
> > > >  	struct rte_hash_parameters hash_cuckoo_params = {
> > > >  		.entries = p->n_keys,
> > > >  		.key_len = p->key_size,
> > > > -		.hash_func = (rte_hash_function)(p->f_hash),
> > > > +		.hash_func = (rte_hash_function) hash_func,
> > > >  		.hash_func_init_val = p->seed,
> > > >  		.socket_id = socket_id,
> > > >  		.name = p->name
> > >
> > > This is just tricking the compiler into not complaining.
> > > I would really rather see the two hash functions made the same.
> >
> > (Adding Bruce as well to consolidate all conversations in a single thread.)
> >
> > What we want to do here is be able to use the librte_hash under the same
> API
> > as the several hash table flavors implemented in librte_table.
> >
> > Both of these libraries allow configuring the hash function per each hash
> > table instance. Problem is: hash function in librte_hash has only 3
> parameters
> > (no key mask), while hash function in librte_table has 4 parameters
> (includes
> > key mask). The key mask helps a lot for practical protocol implementations
> by
> > avoiding key copy & pre-process on lookup.
> >
> > So then: how to plug in librte_hash under the same API as the suite of
> hash
> > tables in librte_table? We don't want to re-implement cuckoo hash from
> > librte_hash, we simply want to invoke it as a low-level primitive, similarly
> > to how the LPM and ACL tables are plugged into librte_table.
> >
> > Solution is: as an exception, pass a 3-parameter hash function to cuckoo
> hash
> > flavor under the librte_table. Maybe this should be documented better.
> This
> > currently triggers a build warning with gcc 8, which is easy to fix, hence
> > this trivial patch.
> >
> > Ideally, for every 3-parameter hash function, I would like to generate the
> > corresponding 4-parameter hash function on-the-fly, but unfortunately this
> is
> > not what C language can do.
> >
> > Of course, IMO the best solution is to add key mask support to librte_hash.
> 
> 
> Looking at the previous discussion I see the following as a possible solution;
> 
> Given the current code looks broken it should be fixed in this release.

The code is not broken. This is not a bug, it is a limitation for that particular table type. The only gap that I see is adding a Doxygen comment in the API header file.

User explicitly picks the hash table type it wants; when using this particular hash table type, that pointer needs to point to a 3-parameter function instead of 4. Given the limitation is clearly documented in Doxygen (current gap that we can quickly address), I don't see any problem.

If people think that this function conversion is not nice, it can be reworked in multiple ways at the expense of API (but not ABI) change:
1. Define the hash function field in the table parameter structure as opaque void * rather than 4-parameter version.
2. Create a separate parameter structure just for this hash table type.

> Given the actual code fix is an API / ABI break (depending on solution) it
> cannot be merged official in this release.
> We have a NEXT_ABI macro - it allows us to break API/ABI conditionally at
> compile time.

This is not new code introduced in this release cycle, this is just fixing the compiler warning, I fail to see how your ABI breakage mention is applicable.

Maybe we should talk more specifics over the code, where exactly in the code would you like to place your NEXT_ABI macro?

> 
> With the above 3 points, I think the best solution is to correctly fix the
> problem that GCC 8 is identifying, and putting that new API inside the NEXT_
> macros.
> 
> In this case, we can preserve backwards (buggy) behavior if required, and
> provide correct (but API/ABI breaking) code as well. This is a tough decision -
> particularly for distros - what do they package?
> 
> Given the current code, I don't see a better solution - but I hope I'm wrong :)

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

[Dumitrescu, Cristian]

> -----Original Message-----
> From: Yigit, Ferruh
> Sent: Monday, April 9, 2018 5:43 PM
> To: Van Haaren, Harry <harry.van.haaren@intel.com>; Dumitrescu, Cristian
> <cristian.dumitrescu@intel.com>; Stephen Hemminger
> <stephen@networkplumber.org>; Singh, Jasvinder
> <jasvinder.singh@intel.com>; Richardson, Bruce
> <bruce.richardson@intel.com>
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8
> 
> On 4/9/2018 5:38 PM, Van Haaren, Harry wrote:
> >> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Dumitrescu,
> Cristian
> >> Sent: Monday, April 9, 2018 4:59 PM
> >> To: Stephen Hemminger <stephen@networkplumber.org>; Singh,
> Jasvinder
> >> <jasvinder.singh@intel.com>; Richardson, Bruce
> <bruce.richardson@intel.com>
> >> Cc: dev@dpdk.org
> >> Subject: Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8
> >>
> >>
> >>
> >>> -----Original Message-----
> >>> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> >>> Sent: Monday, April 9, 2018 4:10 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,  9 Apr 2018 13:49:48 +0100
> >>> Jasvinder Singh <jasvinder.singh@intel.com> 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>
> >>>> ---
> >>>>  lib/librte_table/rte_table_hash_cuckoo.c | 4 +++-
> >>>>  1 file changed, 3 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/lib/librte_table/rte_table_hash_cuckoo.c
> >>> b/lib/librte_table/rte_table_hash_cuckoo.c
> >>>> index dcb4fe9..f7eae27 100644
> >>>> --- a/lib/librte_table/rte_table_hash_cuckoo.c
> >>>> +++ b/lib/librte_table/rte_table_hash_cuckoo.c
> >>>> @@ -103,11 +103,13 @@ rte_table_hash_cuckoo_create(void
> *params,
> >>>>  		return NULL;
> >>>>  	}
> >>>>
> >>>> +	void *hash_func = p->f_hash;
> >>>> +
> >>>>  	/* Create cuckoo hash table */
> >>>>  	struct rte_hash_parameters hash_cuckoo_params = {
> >>>>  		.entries = p->n_keys,
> >>>>  		.key_len = p->key_size,
> >>>> -		.hash_func = (rte_hash_function)(p->f_hash),
> >>>> +		.hash_func = (rte_hash_function) hash_func,
> >>>>  		.hash_func_init_val = p->seed,
> >>>>  		.socket_id = socket_id,
> >>>>  		.name = p->name
> >>>
> >>> This is just tricking the compiler into not complaining.
> >>> I would really rather see the two hash functions made the same.
> >>
> >> (Adding Bruce as well to consolidate all conversations in a single thread.)
> >>
> >> What we want to do here is be able to use the librte_hash under the
> same API
> >> as the several hash table flavors implemented in librte_table.
> >>
> >> Both of these libraries allow configuring the hash function per each hash
> >> table instance. Problem is: hash function in librte_hash has only 3
> parameters
> >> (no key mask), while hash function in librte_table has 4 parameters
> (includes
> >> key mask). The key mask helps a lot for practical protocol
> implementations by
> >> avoiding key copy & pre-process on lookup.
> >>
> >> So then: how to plug in librte_hash under the same API as the suite of
> hash
> >> tables in librte_table? We don't want to re-implement cuckoo hash from
> >> librte_hash, we simply want to invoke it as a low-level primitive, similarly
> >> to how the LPM and ACL tables are plugged into librte_table.
> >>
> >> Solution is: as an exception, pass a 3-parameter hash function to cuckoo
> hash
> >> flavor under the librte_table. Maybe this should be documented better.
> This
> >> currently triggers a build warning with gcc 8, which is easy to fix, hence
> >> this trivial patch.
> >>
> >> Ideally, for every 3-parameter hash function, I would like to generate the
> >> corresponding 4-parameter hash function on-the-fly, but unfortunately
> this is
> >> not what C language can do.
> >>
> >> Of course, IMO the best solution is to add key mask support to
> librte_hash.
> >
> >
> > Looking at the previous discussion I see the following as a possible
> solution;
> >
> > Given the current code looks broken it should be fixed in this release.
> > Given the actual code fix is an API / ABI break (depending on solution) it
> cannot be merged official in this release.
> > We have a NEXT_ABI macro - it allows us to break API/ABI conditionally at
> compile time.
> >
> > With the above 3 points, I think the best solution is to correctly fix the
> problem that GCC 8 is identifying, and putting that new API inside the NEXT_
> macros.
> >
> > In this case, we can preserve backwards (buggy) behavior if required, and
> provide correct (but API/ABI breaking) code as well. This is a tough decision -
> particularly for distros - what do they package?
> 
> +1 to use RTE_NEXT_ABI and deliver fixed code, and agree this is kind of
> pushing
> decision to distros.
> 

Again, where is the bug, and where exactly in the code you want to put RTE_NEXT_ABI macro, and what is the problem fixed by using this macro?

As stated in the reply to Harry, this could be reworked in multiple ways if people think the function pointer conversion is misleading to the user.

> >
> > Given the current code, I don't see a better solution - but I hope I'm wrong
> :)
> >

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

[Ananyev, Konstantin]

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Dumitrescu, Cristian
> Sent: Monday, April 9, 2018 6:02 PM
> To: Van Haaren, Harry <harry.van.haaren@intel.com>; Stephen Hemminger <stephen@networkplumber.org>; Singh, Jasvinder
> <jasvinder.singh@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8
> 
> 
> 
> > -----Original Message-----
> > From: Van Haaren, Harry
> > Sent: Monday, April 9, 2018 5:38 PM
> > To: Dumitrescu, Cristian <cristian.dumitrescu@intel.com>; Stephen
> > Hemminger <stephen@networkplumber.org>; Singh, Jasvinder
> > <jasvinder.singh@intel.com>; Richardson, Bruce
> > <bruce.richardson@intel.com>
> > Cc: dev@dpdk.org
> > Subject: RE: [dpdk-dev] [PATCH] table: fix build error with gcc 8
> >
> > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Dumitrescu,
> > Cristian
> > > Sent: Monday, April 9, 2018 4:59 PM
> > > To: Stephen Hemminger <stephen@networkplumber.org>; Singh,
> > Jasvinder
> > > <jasvinder.singh@intel.com>; Richardson, Bruce
> > <bruce.richardson@intel.com>
> > > Cc: dev@dpdk.org
> > > Subject: Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > > > Sent: Monday, April 9, 2018 4:10 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,  9 Apr 2018 13:49:48 +0100
> > > > Jasvinder Singh <jasvinder.singh@intel.com> 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>
> > > > > ---
> > > > >  lib/librte_table/rte_table_hash_cuckoo.c | 4 +++-
> > > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/lib/librte_table/rte_table_hash_cuckoo.c
> > > > b/lib/librte_table/rte_table_hash_cuckoo.c
> > > > > index dcb4fe9..f7eae27 100644
> > > > > --- a/lib/librte_table/rte_table_hash_cuckoo.c
> > > > > +++ b/lib/librte_table/rte_table_hash_cuckoo.c
> > > > > @@ -103,11 +103,13 @@ rte_table_hash_cuckoo_create(void
> > *params,
> > > > >  		return NULL;
> > > > >  	}
> > > > >
> > > > > +	void *hash_func = p->f_hash;
> > > > > +
> > > > >  	/* Create cuckoo hash table */
> > > > >  	struct rte_hash_parameters hash_cuckoo_params = {
> > > > >  		.entries = p->n_keys,
> > > > >  		.key_len = p->key_size,
> > > > > -		.hash_func = (rte_hash_function)(p->f_hash),
> > > > > +		.hash_func = (rte_hash_function) hash_func,
> > > > >  		.hash_func_init_val = p->seed,
> > > > >  		.socket_id = socket_id,
> > > > >  		.name = p->name
> > > >
> > > > This is just tricking the compiler into not complaining.
> > > > I would really rather see the two hash functions made the same.
> > >
> > > (Adding Bruce as well to consolidate all conversations in a single thread.)
> > >
> > > What we want to do here is be able to use the librte_hash under the same
> > API
> > > as the several hash table flavors implemented in librte_table.
> > >
> > > Both of these libraries allow configuring the hash function per each hash
> > > table instance. Problem is: hash function in librte_hash has only 3
> > parameters
> > > (no key mask), while hash function in librte_table has 4 parameters
> > (includes
> > > key mask). The key mask helps a lot for practical protocol implementations
> > by
> > > avoiding key copy & pre-process on lookup.
> > >
> > > So then: how to plug in librte_hash under the same API as the suite of
> > hash
> > > tables in librte_table? We don't want to re-implement cuckoo hash from
> > > librte_hash, we simply want to invoke it as a low-level primitive, similarly
> > > to how the LPM and ACL tables are plugged into librte_table.
> > >
> > > Solution is: as an exception, pass a 3-parameter hash function to cuckoo
> > hash
> > > flavor under the librte_table. Maybe this should be documented better.
> > This
> > > currently triggers a build warning with gcc 8, which is easy to fix, hence
> > > this trivial patch.
> > >
> > > Ideally, for every 3-parameter hash function, I would like to generate the
> > > corresponding 4-parameter hash function on-the-fly, but unfortunately this
> > is
> > > not what C language can do.
> > >
> > > Of course, IMO the best solution is to add key mask support to librte_hash.
> >
> >
> > Looking at the previous discussion I see the following as a possible solution;
> >
> > Given the current code looks broken it should be fixed in this release.
> 
> The code is not broken. This is not a bug, it is a limitation for that particular table type. The only gap that I see is adding a Doxygen
> comment in the API header file.
> 
> User explicitly picks the hash table type it wants; when using this particular hash table type, that pointer needs to point to a 3-parameter
> function instead of 4. Given the limitation is clearly documented in Doxygen (current gap that we can quickly address), I don't see any
> problem.
> 
> If people think that this function conversion is not nice, it can be reworked in multiple ways at the expense of API (but not ABI) change:
> 1. Define the hash function field in the table parameter structure as opaque void * rather than 4-parameter version.
> 2. Create a separate parameter structure just for this hash table type.

Why just not define your f_hash member as a union:

struct rte_table_hash_params {
...
union {
    rte_table_hash_op_hash  f_hash_4params;
    rte_hash_function f_hash_3_params;
}; 

?

> 
> > Given the actual code fix is an API / ABI break (depending on solution) it
> > cannot be merged official in this release.
> > We have a NEXT_ABI macro - it allows us to break API/ABI conditionally at
> > compile time.
> 
> This is not new code introduced in this release cycle, this is just fixing the compiler warning, I fail to see how your ABI breakage mention is
> applicable.
> 
> Maybe we should talk more specifics over the code, where exactly in the code would you like to place your NEXT_ABI macro?
> 
> >
> > With the above 3 points, I think the best solution is to correctly fix the
> > problem that GCC 8 is identifying, and putting that new API inside the NEXT_
> > macros.
> >
> > In this case, we can preserve backwards (buggy) behavior if required, and
> > provide correct (but API/ABI breaking) code as well. This is a tough decision -
> > particularly for distros - what do they package?
> >
> > Given the current code, I don't see a better solution - but I hope I'm wrong :)

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

[Dumitrescu, Cristian]

> >
> > If people think that this function conversion is not nice, it can be reworked
> in multiple ways at the expense of API (but not ABI) change:
> > 1. Define the hash function field in the table parameter structure as
> opaque void * rather than 4-parameter version.
> > 2. Create a separate parameter structure just for this hash table type.
> 
> Why just not define your f_hash member as a union:
> 
> struct rte_table_hash_params {
> ...
> union {
>     rte_table_hash_op_hash  f_hash_4params;
>     rte_hash_function f_hash_3_params;
> };
> 
> ?
> 

Yes, agreed, this is yet another way to handle this, thanks Konstantin.

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

[Neil Horman]

On Mon, Apr 09, 2018 at 04:38:11PM +0000, Van Haaren, Harry wrote:
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Dumitrescu, Cristian
> > Sent: Monday, April 9, 2018 4:59 PM
> > To: Stephen Hemminger <stephen@networkplumber.org>; Singh, Jasvinder
> > <jasvinder.singh@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8
> > 
> > 
> > 
> > > -----Original Message-----
> > > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > > Sent: Monday, April 9, 2018 4:10 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,  9 Apr 2018 13:49:48 +0100
> > > Jasvinder Singh <jasvinder.singh@intel.com> 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>
> > > > ---
> > > >  lib/librte_table/rte_table_hash_cuckoo.c | 4 +++-
> > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/lib/librte_table/rte_table_hash_cuckoo.c
> > > b/lib/librte_table/rte_table_hash_cuckoo.c
> > > > index dcb4fe9..f7eae27 100644
> > > > --- a/lib/librte_table/rte_table_hash_cuckoo.c
> > > > +++ b/lib/librte_table/rte_table_hash_cuckoo.c
> > > > @@ -103,11 +103,13 @@ rte_table_hash_cuckoo_create(void *params,
> > > >  		return NULL;
> > > >  	}
> > > >
> > > > +	void *hash_func = p->f_hash;
> > > > +
> > > >  	/* Create cuckoo hash table */
> > > >  	struct rte_hash_parameters hash_cuckoo_params = {
> > > >  		.entries = p->n_keys,
> > > >  		.key_len = p->key_size,
> > > > -		.hash_func = (rte_hash_function)(p->f_hash),
> > > > +		.hash_func = (rte_hash_function) hash_func,
> > > >  		.hash_func_init_val = p->seed,
> > > >  		.socket_id = socket_id,
> > > >  		.name = p->name
> > >
> > > This is just tricking the compiler into not complaining.
> > > I would really rather see the two hash functions made the same.
> > 
> > (Adding Bruce as well to consolidate all conversations in a single thread.)
> > 
> > What we want to do here is be able to use the librte_hash under the same API
> > as the several hash table flavors implemented in librte_table.
> > 
> > Both of these libraries allow configuring the hash function per each hash
> > table instance. Problem is: hash function in librte_hash has only 3 parameters
> > (no key mask), while hash function in librte_table has 4 parameters (includes
> > key mask). The key mask helps a lot for practical protocol implementations by
> > avoiding key copy & pre-process on lookup.
> > 
> > So then: how to plug in librte_hash under the same API as the suite of hash
> > tables in librte_table? We don't want to re-implement cuckoo hash from
> > librte_hash, we simply want to invoke it as a low-level primitive, similarly
> > to how the LPM and ACL tables are plugged into librte_table.
> > 
> > Solution is: as an exception, pass a 3-parameter hash function to cuckoo hash
> > flavor under the librte_table. Maybe this should be documented better. This
> > currently triggers a build warning with gcc 8, which is easy to fix, hence
> > this trivial patch.
> > 
> > Ideally, for every 3-parameter hash function, I would like to generate the
> > corresponding 4-parameter hash function on-the-fly, but unfortunately this is
> > not what C language can do.
> > 
> > Of course, IMO the best solution is to add key mask support to librte_hash.
> 
> 
> Looking at the previous discussion I see the following as a possible solution;
> 
> Given the current code looks broken it should be fixed in this release.
> Given the actual code fix is an API / ABI break (depending on solution) it cannot be merged official in this release.
> We have a NEXT_ABI macro - it allows us to break API/ABI conditionally at compile time.
> 
> With the above 3 points, I think the best solution is to correctly fix the problem that GCC 8 is identifying, and putting that new API inside the NEXT_ macros.
> 
> In this case, we can preserve backwards (buggy) behavior if required, and provide correct (but API/ABI breaking) code as well. This is a tough decision - particularly for distros - what do they package?
> 
> Given the current code, I don't see a better solution - but I hope I'm wrong :)
> 
Why not make the hash_func pointer in the rte_hash_parameters structure an
anonymous union, and reserve a bit in the extra_flag field to denote if the
function pointer has 3 arguments or 4?  Then rte_hash_hash can use the
appropriate calling convention on hash_func.

Neil

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

[Van Haaren, Harry]

+CC Neil from other reply

> From: Dumitrescu, Cristian
> Sent: Monday, April 9, 2018 6:27 PM
> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>; Van Haaren, Harry
> <harry.van.haaren@intel.com>; Stephen Hemminger <stephen@networkplumber.org>;
> Singh, Jasvinder <jasvinder.singh@intel.com>; Richardson, Bruce
> <bruce.richardson@intel.com>
> Cc: dev@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH] table: fix build error with gcc 8
> 
> > >
> > > If people think that this function conversion is not nice, it can be
> reworked
> > in multiple ways at the expense of API (but not ABI) change:
> > > 1. Define the hash function field in the table parameter structure as
> > opaque void * rather than 4-parameter version.
> > > 2. Create a separate parameter structure just for this hash table type.
> >
> > Why just not define your f_hash member as a union:
> >
> > struct rte_table_hash_params {
> > ...
> > union {
> >     rte_table_hash_op_hash  f_hash_4params;
> >     rte_hash_function f_hash_3_params;
> > };
> >
> > ?
> >
> 
> Yes, agreed, this is yet another way to handle this, thanks Konstantin.

Agree that this solution is a lot better than raw casting.

The issue I have with casting is that it doesn't explicitly show that the signature is different, and that the code must be aware of that fact. With a union, at least the code explicitly states that there is a difference in signature, and that this is being handled by the code, so this looks a better solution.

Neil proposed an alternative solution using a bit to indicate calling params in a separate reply - another possibility.