[dpdk-dev] [PATCH] gcc compiler option -Og warnings fix

[Wiles, Keith]

>2016-04-01 14:20, Keith Wiles:
>> The new compiler option -Og causes a few warning on variables
>> being used before being set warnings.
>
>Sometimes the compiler is wrong. It seems this option makes it
>even wronger. Why not use -Wno-error with -Og?

Did you want me to make these changes or just request everyone to use -Wno-error with -Og?

If you want a new patch from me on these changes it will be toward the weekend after I get back home from traveling.

>
>More details below:
>
>>  lib/librte_eal/linuxapp/eal/eal_pci_uio.c | 2 +-
>>  lib/librte_lpm/rte_lpm6.c                 | 1 +
>>  lib/librte_vhost/vhost_rxtx.c             | 4 ++--
>
>There are also some warnings in mlx drivers, solved with patch below:
>
>--- a/drivers/net/mlx4/mlx4.c
>+++ b/drivers/net/mlx4/mlx4.c
>@@ -5415,7 +5415,7 @@ mlx4_pci_devinit(struct rte_pci_driver *pci_drv, struct rte_pci_device *pci_dev)
>        int err = 0;
>        struct ibv_context *attr_ctx = NULL;
>        struct ibv_device_attr device_attr;
>-       unsigned int vf;
>+       unsigned int vf = 0;
>        int idx;
>        int i;
> 
>--- a/drivers/net/mlx5/mlx5.c
>+++ b/drivers/net/mlx5/mlx5.c
>@@ -260,8 +260,8 @@ mlx5_pci_devinit(struct rte_pci_driver *pci_drv, struct rte_pci_device *pci_dev)
>        int err = 0;
>        struct ibv_context *attr_ctx = NULL;
>        struct ibv_device_attr device_attr;
>-       unsigned int vf;
>-       unsigned int mps;
>+       unsigned int vf = 0;
>+       unsigned int mps = 0;
>        int idx;
>        int i;
>
>> --- a/lib/librte_eal/linuxapp/eal/eal_pci_uio.c
>> +++ b/lib/librte_eal/linuxapp/eal/eal_pci_uio.c
>> @@ -152,7 +152,7 @@ pci_get_uio_dev(struct rte_pci_device *dev, char *dstbuf,
>>  			   unsigned int buflen, int create)
>>  {
>>  	struct rte_pci_addr *loc = &dev->addr;
>> -	unsigned int uio_num;
>> +	unsigned int uio_num = 0;
>
>This one is OK to fix.
>
>> --- a/lib/librte_lpm/rte_lpm6.c
>> +++ b/lib/librte_lpm/rte_lpm6.c
>> @@ -381,6 +381,7 @@ add_step(struct rte_lpm6 *lpm, struct rte_lpm6_tbl_entry *tbl,
>>  	int8_t bitshift;
>>  	uint8_t bits_covered;
>>  
>> +	*tbl_next = NULL;
>>  	/*
>>  	 * Calculate index to the table based on the number and position
>>  	 * of the bytes being inspected in this step.
>
>It would be more logical to set this variable in the right condition branch:
>--- a/lib/librte_lpm/rte_lpm6.c
>+++ b/lib/librte_lpm/rte_lpm6.c
>@@ -429,6 +429,7 @@ add_step(struct rte_lpm6 *lpm, struct rte_lpm6_tbl_entry *tbl,
>                        }
>                }
> 
>+               *tbl_next = NULL;
>                return 0;
>        }
>
>> --- a/lib/librte_vhost/vhost_rxtx.c
>> +++ b/lib/librte_vhost/vhost_rxtx.c
>> @@ -295,7 +295,7 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
>>  	for (i = 0; i < count; i++) {
>>  		uint16_t desc_idx = desc_indexes[i];
>>  		uint16_t used_idx = (res_start_idx + i) & (vq->size - 1);
>> -		uint32_t copied;
>> +		uint32_t copied = 0;
>
>This variable is not used if copy_mbuf_to_desc fails, so it is always
>initialised before being used.
>We can workaround the silly compiler while avoiding a performance hit
>by resetting the variable only in the error case of copy_mbuf_to_desc:
>
>--- a/lib/librte_vhost/vhost_rxtx.c
>+++ b/lib/librte_vhost/vhost_rxtx.c
>@@ -147,8 +147,10 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
>        struct virtio_net_hdr_mrg_rxbuf virtio_hdr = {{0, 0, 0, 0, 0, 0}, 0};
> 
>        desc = &vq->desc[desc_idx];
>-       if (unlikely(desc->len < vq->vhost_hlen))
>+       if (unlikely(desc->len < vq->vhost_hlen)) {
>+               *copied = 0;
>                return -1;
>+       }
>
>>  		err = copy_mbuf_to_desc(dev, vq, pkts[i], desc_idx, &copied);
>> @@ -531,7 +531,7 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t queue_id,
>>  {
>>  	struct vhost_virtqueue *vq;
>>  	uint32_t pkt_idx = 0, nr_used = 0;
>> -	uint16_t start, end;
>> +	uint16_t start = 0, end = 0;
>
>I don't understand this one because the variables are not used if
>reserve_avail_buf_mergeable fails.
>I don't see any smart workaround.
>Huawei, Yuanhan, can we expect a little slowdown with this change?
>
>


Regards,
Keith