[dpdk-dev] [PATCH] gcc compiler option -Og warnings fix
Wiles, Keith
keith.wiles at intel.com
Tue Apr 5 01:03:20 CEST 2016
>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
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