linux-kernel - Re: -Wsometimes-uninitialized Clang warning in drivers/net/ethernet/broadcom/bnxt/bnxt.c

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Date:   Wed, 20 Mar 2019 12:08:49 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Michael Chan <michael.chan@...adcom.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com
Subject: Re: -Wsometimes-uninitialized Clang warning in
 drivers/net/ethernet/broadcom/bnxt/bnxt.c

On Thu, Mar 07, 2019 at 05:57:35PM -0700, Nathan Chancellor wrote:
> Hi all,
> 
> We are trying to get Clang's -Wsometimes-uninitialized turned on for the
> kernel as it can catch some bugs that GCC can't. This warning came up:
> 
> drivers/net/ethernet/broadcom/bnxt/bnxt.c:1612:6: warning: variable 'len' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
>         if (rxcmp1->rx_cmp_cfa_code_errors_v2 & RX_CMP_L2_ERRORS) {
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/net/ethernet/broadcom/bnxt/bnxt.c:1703:19: note: uninitialized use occurs here
>         cpr->rx_bytes += len;
>                          ^~~
> drivers/net/ethernet/broadcom/bnxt/bnxt.c:1612:2: note: remove the 'if' if its condition is always false
>         if (rxcmp1->rx_cmp_cfa_code_errors_v2 & RX_CMP_L2_ERRORS) {
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/net/ethernet/broadcom/bnxt/bnxt.c:1540:18: note: initialize the variable 'len' to silence this warning
>         unsigned int len;
>                         ^
>                          = 0
> 1 warning generated.
> 
> It seems like the logical change to make is this; however, I am not sure
> if this has any other unintended consequences since this is a rather
> dense function. I would much appreciate your input, especially if there
> is a better way to fix it.
> 
> Cheers,
> Nathan
> 
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> index 0bb9d7b3a2b6..7d3d206c2e86 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> @@ -1615,7 +1615,7 @@ static int bnxt_rx_pkt(struct bnxt *bp, struct bnxt_cp_ring_info *cpr,
>                         bnxt_reuse_rx_agg_bufs(cpr, cp_cons, agg_bufs);
>  
>                 rc = -EIO;
> -               goto next_rx;
> +               goto next_rx_no_prod_no_len;
>         }
>  
>         len = le32_to_cpu(rxcmp->rx_cmp_len_flags_type) >> RX_CMP_LEN_SHIFT;

Gentle ping (if there was a response to this, I didn't receive it). I
know I sent it in the middle of a merge window so I get if it slipped
through the cracks.

Thanks,
Nathan