netdev - Re: [PATCH] iwlwifi: pcie: fix constant-conversion warning

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Date:   Thu, 11 Nov 2021 08:33:34 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Luca Coelho <luciano.coelho@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Johannes Berg <johannes.berg@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Yaara Baruch <yaara.baruch@...el.com>,
        Matti Gottlieb <matti.gottlieb@...el.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] iwlwifi: pcie: fix constant-conversion warning

On Wed, Nov 10, 2021 at 10:38 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Thu, Nov 4, 2021 at 6:37 AM Arnd Bergmann <arnd@...nel.org> wrote:
> >
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > clang points out a potential issue with integer overflow when
> > the iwl_dev_info_table[] array is empty:
> >
> > drivers/net/wireless/intel/iwlwifi/pcie/drv.c:1344:42: error: implicit conversion from 'unsigned long' to 'int' changes value from 18446744073709551615 to -1 [-Werror,-Wconstant-conversion]
> >         for (i = ARRAY_SIZE(iwl_dev_info_table) - 1; i >= 0; i--) {
> >                ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
> >
> > This is still harmless, as the loop correctly terminates, but adding
> > an (int) cast makes that clearer to the compiler.
> >
> > Fixes: 3f7320428fa4 ("iwlwifi: pcie: simplify iwl_pci_find_dev_info()")
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > ---
> >  drivers/net/wireless/intel/iwlwifi/pcie/drv.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/drv.c b/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
> > index c574f041f096..81e8f2fc4982 100644
> > --- a/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
> > +++ b/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
> > @@ -1341,7 +1341,7 @@ iwl_pci_find_dev_info(u16 device, u16 subsystem_device,
> >  {
> >         int i;
> >
> > -       for (i = ARRAY_SIZE(iwl_dev_info_table) - 1; i >= 0; i--) {
> > +       for (i = (int)ARRAY_SIZE(iwl_dev_info_table) - 1; i >= 0; i--) {
>
> Perhaps `i` could be a `size_t` instead of an `int`?
>
> size_t i = ARRAY_SIZE(iwl_dev_info_table);
> while (i--) {
>   ...

I imagine 'i' is idiomatically 'int' in inner iterations.

I've sent a different fix now.

        Arnd