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

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2016-04-04 23:03, 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?

I was suggesting that everyone can use -Wno-error when using -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.

If some driver maintainers think there are some things to fix,
they are free to send a patch by themselves before the end of the week.

> >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
> 
> 
> 
>