Re: [PATCH] ixgbe: fix build with gcc 4.4

[Vlad Zolotarov <vladz-RmZWMc9puTNJc61us3aD9laTQe2KTcn/@public.gmane.org>]

On 04/14/15 16:06, Ananyev, Konstantin wrote:
>
>> -----Original Message-----
>> From: Vlad Zolotarov [mailto:vladz-RmZWMc9puTNJc61us3aD9laTQe2KTcn/@public.gmane.org]
>> Sent: Tuesday, April 14, 2015 1:49 PM
>> To: Thomas Monjalon; Ananyev, Konstantin; Zhang, Helin
>> Cc: dev-VfR2kkLFssw@public.gmane.org
>> Subject: Re: [PATCH] ixgbe: fix build with gcc 4.4
>>
>>
>>
>> On 04/14/15 12:31, Thomas Monjalon wrote:
>>> With GCC 4.4.7 from CentOS 6.5, the following errors arise:
>>>
>>> lib/librte_pmd_ixgbe/ixgbe_rxtx.c: In function ‘ixgbe_dev_rx_queue_setup’:
>>> lib/librte_pmd_ixgbe/ixgbe_rxtx.c:2509: error: missing initializer
>>> lib/librte_pmd_ixgbe/ixgbe_rxtx.c:2509: error: (near initialization for ‘dev_info.driver_name’)
>>>
>>> lib/librte_pmd_ixgbe/ixgbe_rxtx.c: In function ‘ixgbe_set_rsc’:
>>> lib/librte_pmd_ixgbe/ixgbe_rxtx.c:4072: error: missing initializer
>>> lib/librte_pmd_ixgbe/ixgbe_rxtx.c:4072: error: (near initialization for ‘dev_info.driver_name’)
>>>
>>> lib/librte_pmd_ixgbe/ixgbe_rxtx.c: In function ‘ixgbe_recv_pkts_lro_single_alloc’:
>>> lib/librte_pmd_ixgbe/ixgbe_rxtx.c:1479: error: ‘next_rsc_entry’ may be used uninitialized in this function
>>> lib/librte_pmd_ixgbe/ixgbe_rxtx.c:1480: error: ‘next_rxe’ may be used uninitialized in this function
>>>
>>> Fixes: 8eecb3295aed ("ixgbe: add LRO support")
>>>
>>> Signed-off-by: Thomas Monjalon <thomas.monjalon-pdR9zngts4EAvxtiuMwx3w@public.gmane.org>
>>> ---
>>>    lib/librte_pmd_ixgbe/ixgbe_rxtx.c | 8 ++++----
>>>    1 file changed, 4 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
>>> index f1da9ec..a2b8631 100644
>>> --- a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
>>> +++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
>>> @@ -1476,8 +1476,8 @@ ixgbe_recv_pkts_lro(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts,
>>>    		bool eop;
>>>    		struct ixgbe_rx_entry *rxe;
>>>    		struct ixgbe_rsc_entry *rsc_entry;
>>> -		struct ixgbe_rsc_entry *next_rsc_entry;
>>> -		struct ixgbe_rx_entry *next_rxe;
>>> +		struct ixgbe_rsc_entry *next_rsc_entry = NULL;
>>> +		struct ixgbe_rx_entry *next_rxe = NULL;
>>>    		struct rte_mbuf *first_seg;
>>>    		struct rte_mbuf *rxm;
>>>    		struct rte_mbuf *nmb;
>>> @@ -2506,7 +2506,7 @@ ixgbe_dev_rx_queue_setup(struct rte_eth_dev *dev,
>>>    	struct ixgbe_rx_queue *rxq;
>>>    	struct ixgbe_hw     *hw;
>>>    	uint16_t len;
>>> -	struct rte_eth_dev_info dev_info = { 0 };
>>> +	struct rte_eth_dev_info dev_info = { .max_rx_queues = 0 };
>>>    	struct rte_eth_rxmode *dev_rx_mode = &dev->data->dev_conf.rxmode;
>>>    	bool rsc_requested = false;
>>>
>>> @@ -4069,7 +4069,7 @@ ixgbe_set_rsc(struct rte_eth_dev *dev)
>>>    {
>>>    	struct rte_eth_rxmode *rx_conf = &dev->data->dev_conf.rxmode;
>>>    	struct ixgbe_hw *hw = IXGBE_DEV_PRIVATE_TO_HW(dev->data->dev_private);
>>> -	struct rte_eth_dev_info dev_info = { 0 };
>>> +	struct rte_eth_dev_info dev_info = { .max_rx_queues = 0 };
>> Hmmm... Unless I miss something this and one above would zero only a
>> single field - "max_rx_queues"; and would leave the rest uninitialized.
>> The original code intend to zero the whole struct. The alternative to
>> the original lines could be usage of memset().
> As I understand, in that case compiler had to set all non-explicitly initialised members to 0.
> So I think we are ok here.

Yeah, I guess it does zero-initializes the rest 
(https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html) however I 
don't understand how the above change fixes the error if it complains 
about the dev_info.driver_name?

What I'm trying to say - the proposed fix is completely unclear and 
confusing. Think of somebody reading this line in a month from today - 
he wouldn't get a clue why is it there, why to explicitly set 
max_rx_queues to zero and leave the rest be zeroed automatically... Why 
to add such artifacts to the code instead of just zeroing the struct 
with a memset() and putting a good clear comment above it explaining why 
we use a memset() and not and initializer?

>   
>>>    	bool rsc_capable = false;
>>>    	uint16_t i;
>>>    	uint32_t rdrxctl;