[dpdk-dev,08/10] lpm6: fix compilation with -Og

  The compilation with gcc-6.3.0 and EXTRA_CFLAGS=-Og gives the following
error:

  CC rte_lpm6.o
  rte_lpm6.c: In function ‘rte_lpm6_add_v1705’:
  rte_lpm6.c:442:11: error: ‘tbl_next’ may be used uninitialized in
                             this function [-Werror=maybe-uninitialized]
     if (!tbl[tbl_index].valid) {
             ^
  rte_lpm6.c:521:29: note: ‘tbl_next’ was declared here
    struct rte_lpm6_tbl_entry *tbl_next;
                               ^~~~~~~~

This is a false positive from gcc. Fix it by initializing tbl_next
to NULL.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
---
 lib/librte_lpm/rte_lpm6.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
  

On 9/11/2017 4:13 PM, Olivier Matz wrote:
> The compilation with gcc-6.3.0 and EXTRA_CFLAGS=-Og gives the following
> error:
> 
>   CC rte_lpm6.o
>   rte_lpm6.c: In function ‘rte_lpm6_add_v1705’:
>   rte_lpm6.c:442:11: error: ‘tbl_next’ may be used uninitialized in
>                              this function [-Werror=maybe-uninitialized]
>      if (!tbl[tbl_index].valid) {
>              ^
>   rte_lpm6.c:521:29: note: ‘tbl_next’ was declared here
>     struct rte_lpm6_tbl_entry *tbl_next;
>                                ^~~~~~~~
> 
> This is a false positive from gcc. Fix it by initializing tbl_next
> to NULL.

This is hard to trace, and it seems there is a way to have it, not sure
practically possible:

rte_lpm6_add_v1705
    add_step
        if (depth <= bits_covered) {
            ...
            return 0 <--- so tbl_next stays untouched.
    tbl = tbl_next
    add_step
        tbl[tbl_index]


So same comment as previous, if there is a practically available path,
this patch makes it harder to find by hiding compiler warning, so adding
maintainer for decision.


> 
> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> ---
>  lib/librte_lpm/rte_lpm6.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/librte_lpm/rte_lpm6.c b/lib/librte_lpm/rte_lpm6.c
> index b4a7df348..f9496fe1b 100644
> --- a/lib/librte_lpm/rte_lpm6.c
> +++ b/lib/librte_lpm/rte_lpm6.c
> @@ -518,7 +518,7 @@ rte_lpm6_add_v1705(struct rte_lpm6 *lpm, uint8_t *ip, uint8_t depth,
>  		uint32_t next_hop)
>  {
>  	struct rte_lpm6_tbl_entry *tbl;
> -	struct rte_lpm6_tbl_entry *tbl_next;
> +	struct rte_lpm6_tbl_entry *tbl_next = NULL;
>  	int32_t rule_index;
>  	int status;
>  	uint8_t masked_ip[RTE_LPM6_IPV6_ADDR_SIZE];
>
  

On Fri, Oct 06, 2017 at 01:18:00AM +0100, Ferruh Yigit wrote:
> On 9/11/2017 4:13 PM, Olivier Matz wrote:
> > The compilation with gcc-6.3.0 and EXTRA_CFLAGS=-Og gives the following
> > error:
> > 
> >   CC rte_lpm6.o
> >   rte_lpm6.c: In function ‘rte_lpm6_add_v1705’:
> >   rte_lpm6.c:442:11: error: ‘tbl_next’ may be used uninitialized in
> >                              this function [-Werror=maybe-uninitialized]
> >      if (!tbl[tbl_index].valid) {
> >              ^
> >   rte_lpm6.c:521:29: note: ‘tbl_next’ was declared here
> >     struct rte_lpm6_tbl_entry *tbl_next;
> >                                ^~~~~~~~
> > 
> > This is a false positive from gcc. Fix it by initializing tbl_next
> > to NULL.
> 
> This is hard to trace, and it seems there is a way to have it, not sure
> practically possible:
> 
> rte_lpm6_add_v1705
>     add_step
>         if (depth <= bits_covered) {
>             ...
>             return 0 <--- so tbl_next stays untouched.
>     tbl = tbl_next
>     add_step
>         tbl[tbl_index]
> 
> 
> So same comment as previous, if there is a practically available path,
> this patch makes it harder to find by hiding compiler warning, so adding
> maintainer for decision.
> 
> 
+Cristian, who has more knowledge of this library than I.

I don't think there is an issue here, since there is an additional check
before the second and subsequent calls to add_step(). The condition
check on the loop in add_v1705 is:

"i < RTE_LPM6_IPV6_ADDR_SIZE && status == 1;"

The "return 0" sets status to 0, causing the loop to break, preventing
any more calls to "tbl = tbl_next".

Therefore I don't think this masks an issue, and the fix is ok.

In the absense of any other objections or comments on this from
Cristian:

Acked-by: Bruce Richardson <bruce.richardson@intel.com>
  

On 9/11/2017 8:13 AM, Olivier Matz wrote:
> The compilation with gcc-6.3.0 and EXTRA_CFLAGS=-Og gives the following
> error:
> 
>   CC rte_lpm6.o
>   rte_lpm6.c: In function ‘rte_lpm6_add_v1705’:
>   rte_lpm6.c:442:11: error: ‘tbl_next’ may be used uninitialized in
>                              this function [-Werror=maybe-uninitialized]
>      if (!tbl[tbl_index].valid) {
>              ^
>   rte_lpm6.c:521:29: note: ‘tbl_next’ was declared here
>     struct rte_lpm6_tbl_entry *tbl_next;
>                                ^~~~~~~~
> 
> This is a false positive from gcc. Fix it by initializing tbl_next
> to NULL.
> 
> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>

> Acked-by: Bruce Richardson <bruce.richardson@intel.com>
Applied to dpdk-next-net/master, thanks.