[PATCH] pinctrl: sunxi: fix theoretical uninitialized variable access

[PATCH] pinctrl: sunxi: fix theoretical uninitialized variable access

[Arnd Bergmann]

gcc warns about a  way that it could use an uninitialized variable:

drivers/pinctrl/sunxi/pinctrl-sunxi.c: In function 'sunxi_pinctrl_init':
drivers/pinctrl/sunxi/pinctrl-sunxi.c:1191:8: error: 'best_div' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This cannot really happen except if 'freq' is UINT_MAX and 'clock' is
zero, and both of these are forbidden. To shut up the warning anyway,
this changes the logic to initialize the return code to the first
divider value before looking at the others.

Fixes: 7c926492d38a ("pinctrl: sunxi: Add support for interrupt debouncing")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/pinctrl/sunxi/pinctrl-sunxi.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/pinctrl/sunxi/pinctrl-sunxi.c b/drivers/pinctrl/sunxi/pinctrl-sunxi.c
index 2339d4718b4d..6b7953da4228 100644
--- a/drivers/pinctrl/sunxi/pinctrl-sunxi.c
+++ b/drivers/pinctrl/sunxi/pinctrl-sunxi.c
@@ -1125,10 +1125,13 @@ static int sunxi_pinctrl_build_state(struct platform_device *pdev)
 static int sunxi_pinctrl_get_debounce_div(struct clk *clk, int freq, int *diff)
 {
 	unsigned long clock = clk_get_rate(clk);
-	unsigned int best_diff = ~0, best_div;
+	unsigned int best_diff, best_div;
 	int i;
 
-	for (i = 0; i < 8; i++) {
+	best_diff = abs(freq - clock);
+	best_div = 0;
+
+	for (i = 1; i < 8; i++) {
 		int cur_diff = abs(freq - (clock >> i));
 
 		if (cur_diff < best_diff) {
-- 
2.9.0

Re: [PATCH] pinctrl: sunxi: fix theoretical uninitialized variable access

[Linus Walleij]

On Wed, Nov 16, 2016 at 3:18 PM, Arnd Bergmann <arnd@arndb.de> wrote:

> gcc warns about a  way that it could use an uninitialized variable:
>
> drivers/pinctrl/sunxi/pinctrl-sunxi.c: In function 'sunxi_pinctrl_init':
> drivers/pinctrl/sunxi/pinctrl-sunxi.c:1191:8: error: 'best_div' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>
> This cannot really happen except if 'freq' is UINT_MAX and 'clock' is
> zero, and both of these are forbidden. To shut up the warning anyway,
> this changes the logic to initialize the return code to the first
> divider value before looking at the others.
>
> Fixes: 7c926492d38a ("pinctrl: sunxi: Add support for interrupt debouncing")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Patch applied.

Yours,
Linus Walleij

Re: [PATCH] pinctrl: sunxi: fix theoretical uninitialized variable access

[Maxime Ripard]

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Hi Arnd,

On Wed, Nov 16, 2016 at 03:18:18PM +0100, Arnd Bergmann wrote:
> gcc warns about a  way that it could use an uninitialized variable:
> 
> drivers/pinctrl/sunxi/pinctrl-sunxi.c: In function 'sunxi_pinctrl_init':
> drivers/pinctrl/sunxi/pinctrl-sunxi.c:1191:8: error: 'best_div' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> This cannot really happen except if 'freq' is UINT_MAX and 'clock' is
> zero, and both of these are forbidden. To shut up the warning anyway,
> this changes the logic to initialize the return code to the first
> divider value before looking at the others.
> 
> Fixes: 7c926492d38a ("pinctrl: sunxi: Add support for interrupt debouncing")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Thanks for that patch.

Just out of curiosity, which gcc gives those warnings? I have 6.2 and
it didn't output anything..

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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Re: [PATCH] pinctrl: sunxi: fix theoretical uninitialized variable access

[Linus Walleij]

On Wed, Nov 16, 2016 at 9:33 PM, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:

> On Wed, Nov 16, 2016 at 03:18:18PM +0100, Arnd Bergmann wrote:
>> gcc warns about a  way that it could use an uninitialized variable:
>>
>> drivers/pinctrl/sunxi/pinctrl-sunxi.c: In function 'sunxi_pinctrl_init':
>> drivers/pinctrl/sunxi/pinctrl-sunxi.c:1191:8: error: 'best_div' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>>
>> This cannot really happen except if 'freq' is UINT_MAX and 'clock' is
>> zero, and both of these are forbidden. To shut up the warning anyway,
>> this changes the logic to initialize the return code to the first
>> divider value before looking at the others.
>>
>> Fixes: 7c926492d38a ("pinctrl: sunxi: Add support for interrupt debouncing")
>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> Thanks for that patch.
>
> Just out of curiosity, which gcc gives those warnings? I have 6.2 and
> it didn't output anything..

Context: Arnd re-enabled -Werror=maybe-uninitialized
in the kernel build and this kind of stuff started to appear so
it needs to be fixed up.

Yours,
Linus Walleij

Re: [PATCH] pinctrl: sunxi: fix theoretical uninitialized variable access

[Arnd Bergmann]

On Thursday, November 17, 2016 10:08:28 AM CET Linus Walleij wrote:
> On Wed, Nov 16, 2016 at 9:33 PM, Maxime Ripard
> <maxime.ripard@free-electrons.com> wrote:
> 
> > On Wed, Nov 16, 2016 at 03:18:18PM +0100, Arnd Bergmann wrote:
> >> gcc warns about a  way that it could use an uninitialized variable:
> >>
> >> drivers/pinctrl/sunxi/pinctrl-sunxi.c: In function 'sunxi_pinctrl_init':
> >> drivers/pinctrl/sunxi/pinctrl-sunxi.c:1191:8: error: 'best_div' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> >>
> >> This cannot really happen except if 'freq' is UINT_MAX and 'clock' is
> >> zero, and both of these are forbidden. To shut up the warning anyway,
> >> this changes the logic to initialize the return code to the first
> >> divider value before looking at the others.
> >>
> >> Fixes: 7c926492d38a ("pinctrl: sunxi: Add support for interrupt debouncing")
> >> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> >
> > Thanks for that patch.
> >
> > Just out of curiosity, which gcc gives those warnings? I have 6.2 and
> > it didn't output anything..
> 
> Context: Arnd re-enabled -Werror=maybe-uninitialized
> in the kernel build and this kind of stuff started to appear so
> it needs to be fixed up.

Right, it was disabled from linux-4.8-rc1 to linux-4.9-rc4 and is now back
in the default builds when using gcc-4.9 or higher. You should get the
warning if you test with linux-next or -rc4.

	Arnd

Re: [PATCH] pinctrl: sunxi: fix theoretical uninitialized variable access

[Maxime Ripard]

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On Thu, Nov 17, 2016 at 10:08:28AM +0100, Linus Walleij wrote:
> On Wed, Nov 16, 2016 at 9:33 PM, Maxime Ripard
> <maxime.ripard@free-electrons.com> wrote:
> 
> > On Wed, Nov 16, 2016 at 03:18:18PM +0100, Arnd Bergmann wrote:
> >> gcc warns about a  way that it could use an uninitialized variable:
> >>
> >> drivers/pinctrl/sunxi/pinctrl-sunxi.c: In function 'sunxi_pinctrl_init':
> >> drivers/pinctrl/sunxi/pinctrl-sunxi.c:1191:8: error: 'best_div' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> >>
> >> This cannot really happen except if 'freq' is UINT_MAX and 'clock' is
> >> zero, and both of these are forbidden. To shut up the warning anyway,
> >> this changes the logic to initialize the return code to the first
> >> divider value before looking at the others.
> >>
> >> Fixes: 7c926492d38a ("pinctrl: sunxi: Add support for interrupt debouncing")
> >> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> >
> > Thanks for that patch.
> >
> > Just out of curiosity, which gcc gives those warnings? I have 6.2 and
> > it didn't output anything..
> 
> Context: Arnd re-enabled -Werror=maybe-uninitialized
> in the kernel build and this kind of stuff started to appear so
> it needs to be fixed up.

Ah, that makes sense. Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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