[PATCH] [v3] iwlwifi: pcie: fix constant-conversion warning

[PATCH] [v3] iwlwifi: pcie: fix constant-conversion warning

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

gcc-11 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 extra range check makes that obvious to both readers and to the
compiler.

Fixes: 3f7320428fa4 ("iwlwifi: pcie: simplify iwl_pci_find_dev_info()")
Reported-by: kernel test robot <lkp@intel.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
Changes in v3:
- make it actually work with gcc-11
- fix commit message s/clang/gcc-11/

Changes in v2:
- replace int cast with a range check
---
 drivers/net/wireless/intel/iwlwifi/pcie/drv.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/drv.c b/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
index c574f041f096..395e328c6a07 100644
--- a/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
+++ b/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
@@ -1339,9 +1339,13 @@ iwl_pci_find_dev_info(u16 device, u16 subsystem_device,
 		      u16 mac_type, u8 mac_step,
 		      u16 rf_type, u8 cdb, u8 rf_id, u8 no_160, u8 cores)
 {
+	int num_devices = ARRAY_SIZE(iwl_dev_info_table);
 	int i;
 
-	for (i = ARRAY_SIZE(iwl_dev_info_table) - 1; i >= 0; i--) {
+	if (!num_devices)
+		return NULL;
+
+	for (i = num_devices - 1; i >= 0; i--) {
 		const struct iwl_dev_info *dev_info = &iwl_dev_info_table[i];
 
 		if (dev_info->device != (u16)IWL_CFG_ANY &&
-- 
2.29.2

Re: [PATCH] [v3] iwlwifi: pcie: fix constant-conversion warning

[Nathan Chancellor]

On Thu, Nov 18, 2021 at 03:21:02PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> gcc-11 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--) {
>                ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~

For what it's worth, I do see this warning with Clang when both
CONFIG_IWLDVM and CONFIG_IWLMVM are disabled and looking through the GCC
warning docs [1], I do not see a -Wconstant-conversion option? Maybe
there is another warning that is similar but that warning right there
appears to have come from clang, as it matches mine exactly.

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--) {
               ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
1 error generated.

[1]: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

> This is still harmless, as the loop correctly terminates, but adding
> an extra range check makes that obvious to both readers and to the
> compiler.
> 
> Fixes: 3f7320428fa4 ("iwlwifi: pcie: simplify iwl_pci_find_dev_info()")
> Reported-by: kernel test robot <lkp@intel.com>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Regardless of above, this resolves the warning for clang.

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
> Changes in v3:
> - make it actually work with gcc-11
> - fix commit message s/clang/gcc-11/
> 
> Changes in v2:
> - replace int cast with a range check
> ---
>  drivers/net/wireless/intel/iwlwifi/pcie/drv.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/drv.c b/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
> index c574f041f096..395e328c6a07 100644
> --- a/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
> +++ b/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
> @@ -1339,9 +1339,13 @@ iwl_pci_find_dev_info(u16 device, u16 subsystem_device,
>  		      u16 mac_type, u8 mac_step,
>  		      u16 rf_type, u8 cdb, u8 rf_id, u8 no_160, u8 cores)
>  {
> +	int num_devices = ARRAY_SIZE(iwl_dev_info_table);
>  	int i;
>  
> -	for (i = ARRAY_SIZE(iwl_dev_info_table) - 1; i >= 0; i--) {
> +	if (!num_devices)
> +		return NULL;
> +
> +	for (i = num_devices - 1; i >= 0; i--) {
>  		const struct iwl_dev_info *dev_info = &iwl_dev_info_table[i];
>  
>  		if (dev_info->device != (u16)IWL_CFG_ANY &&
> -- 
> 2.29.2
> 

Re: [PATCH] [v3] iwlwifi: pcie: fix constant-conversion warning

[Arnd Bergmann]

On Thu, Nov 18, 2021 at 5:03 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> On Thu, Nov 18, 2021 at 03:21:02PM +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > gcc-11 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--) {
> >                ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
>
> For what it's worth, I do see this warning with Clang when both
> CONFIG_IWLDVM and CONFIG_IWLMVM are disabled and looking through the GCC
> warning docs [1], I do not see a -Wconstant-conversion option? Maybe
> there is another warning that is similar but that warning right there
> appears to have come from clang, as it matches mine exactly.
>
> 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--) {
>                ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
> 1 error generated.
>
> [1]: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

Ok, got it: it turns out this warning /also/ happens with gcc-11 and
the initial changelog was the one for matching the clang warning.
This is the gcc output, which is very similar but has a different
warning option.

drivers/net/wireless/intel/iwlwifi/pcie/drv.c: In function
'iwl_pci_find_dev_info':
include/linux/kernel.h:46:25: error: overflow in conversion from 'long
unsigned int' to 'int' changes value from '18446744073709551615' to
'-1' [-Werror=overflow]
   46 | #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) +
__must_be_array(arr))
      |                         ^
drivers/net/wireless/intel/iwlwifi/pcie/drv.c:1344:18: note: in
expansion of macro 'ARRAY_SIZE'
 1344 |         for (i = ARRAY_SIZE(iwl_dev_info_table) - 1; i >= 0; i--) {

My v2 patch only addressed the clang warning, while v3 works with both
gcc and clang. I can send a v4 if I should update the changelog again
to explain that, but I suppose it's still close enough.

      Arnd

Re: [v3] iwlwifi: pcie: fix constant-conversion warning

[Kalle Valo]

Arnd Bergmann <arnd@kernel.org> wrote:

> From: Arnd Bergmann <arnd@arndb.de>
> 
> Both gcc-11 and clang point out a potential issue with integer overflow when
> the iwl_dev_info_table[] array is empty. This is what clang warns:
> 
> 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 extra range check makes that obvious to both readers and to the
> compiler.
> 
> Fixes: 3f7320428fa4 ("iwlwifi: pcie: simplify iwl_pci_find_dev_info()")
> Reported-by: kernel test robot <lkp@intel.com>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>

Patch applied to wireless-drivers.git, thanks.

fe785f56ad58 iwlwifi: pcie: fix constant-conversion warning

-- 
https://patchwork.kernel.org/project/linux-wireless/patch/20211118142124.526901-1-arnd@kernel.org/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches