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

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Date:   Wed, 20 Mar 2019 13:41:03 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Michael Chan <michael.chan@...adcom.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com, eddie.wai@...adcom.com,
        huangjw@...adcom.com, prashant@...adcom.com, mchan@...adcom.com,
        vasundhara-v.volam@...adcom.com
Subject: Re: -Wsometimes-uninitialized Clang warning in drivers/net/ethernet/broadcom/bnxt/bnxt.c

+ Broadcom folks from commit c0c050c58d84 ("bnxt_en: New Broadcom
ethernet driver.").  Looks like Michael wrote and is still maintaining
the driver.

On Wed, Mar 20, 2019 at 12:08 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> 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.

I agree that `goto next_rx_no_prod_no_len` appears to be most correct;
though I don't understand why this function is a mix of early return
codes, vs setting rc then updating *raw_cons.  The alternative is
probably zero initializing len, but I'm not sure whether *raw_cons
should be updated in that case or not.  Thanks for bringing this up
and the patch.  Sorry for the delay in review.  Can folks at Broadcom
please clarify?

-- 
Thanks,
~Nick Desaulniers