* [PATCH] Input: tca8418_keypad: hide gcc-4.9 -Wmaybe-uninitialized warning
@ 2016-10-24 15:32 Arnd Bergmann
2016-10-24 23:45 ` Dmitry Torokhov
0 siblings, 1 reply; 4+ messages in thread
From: Arnd Bergmann @ 2016-10-24 15:32 UTC (permalink / raw)
To: Dmitry Torokhov; +Cc: Arnd Bergmann, linux-input, linux-kernel
Older versions of gcc warn about the tca8418_irq_handler function
as they can't keep track of the variable assignment inside of the
loop when using the -Wmaybe-unintialized flag:
drivers/input/keyboard/tca8418_keypad.c: In function ‘tca8418_irq_handler’:
drivers/input/keyboard/tca8418_keypad.c:172:9: error: ‘reg’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/input/keyboard/tca8418_keypad.c:165:5: note: ‘reg’ was declared here
This is fixed in gcc-6, but it's possible to rearrange the code
in a way that avoids the warning on older compilers as well.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
drivers/input/keyboard/tca8418_keypad.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/drivers/input/keyboard/tca8418_keypad.c b/drivers/input/keyboard/tca8418_keypad.c
index 9002298698fc..3048ef3e3e16 100644
--- a/drivers/input/keyboard/tca8418_keypad.c
+++ b/drivers/input/keyboard/tca8418_keypad.c
@@ -164,11 +164,18 @@ static void tca8418_read_keypad(struct tca8418_keypad *keypad_data)
int error, col, row;
u8 reg, state, code;
- /* Initial read of the key event FIFO */
- error = tca8418_read_byte(keypad_data, REG_KEY_EVENT_A, ®);
+ do {
+ error = tca8418_read_byte(keypad_data, REG_KEY_EVENT_A, ®);
+ if (error < 0) {
+ dev_err(&keypad_data->client->dev,
+ "unable to read REG_KEY_EVENT_A\n");
+ break;
+ }
+
+ /* Assume that key code 0 signifies empty FIFO */
+ if (reg <= 0)
+ break;
- /* Assume that key code 0 signifies empty FIFO */
- while (error >= 0 && reg > 0) {
state = reg & KEY_EVENT_VALUE;
code = reg & KEY_EVENT_CODE;
@@ -184,11 +191,7 @@ static void tca8418_read_keypad(struct tca8418_keypad *keypad_data)
/* Read for next loop */
error = tca8418_read_byte(keypad_data, REG_KEY_EVENT_A, ®);
- }
-
- if (error < 0)
- dev_err(&keypad_data->client->dev,
- "unable to read REG_KEY_EVENT_A\n");
+ } while (1);
input_sync(input);
}
--
2.9.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] Input: tca8418_keypad: hide gcc-4.9 -Wmaybe-uninitialized warning
2016-10-24 15:32 [PATCH] Input: tca8418_keypad: hide gcc-4.9 -Wmaybe-uninitialized warning Arnd Bergmann
@ 2016-10-24 23:45 ` Dmitry Torokhov
2016-10-25 9:59 ` Arnd Bergmann
0 siblings, 1 reply; 4+ messages in thread
From: Dmitry Torokhov @ 2016-10-24 23:45 UTC (permalink / raw)
To: Arnd Bergmann; +Cc: linux-input, linux-kernel
Hi Arnd,
On Mon, Oct 24, 2016 at 05:32:08PM +0200, Arnd Bergmann wrote:
> Older versions of gcc warn about the tca8418_irq_handler function
> as they can't keep track of the variable assignment inside of the
> loop when using the -Wmaybe-unintialized flag:
>
> drivers/input/keyboard/tca8418_keypad.c: In function ‘tca8418_irq_handler’:
> drivers/input/keyboard/tca8418_keypad.c:172:9: error: ‘reg’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/input/keyboard/tca8418_keypad.c:165:5: note: ‘reg’ was declared here
>
> This is fixed in gcc-6, but it's possible to rearrange the code
> in a way that avoids the warning on older compilers as well.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> drivers/input/keyboard/tca8418_keypad.c | 21 ++++++++++++---------
> 1 file changed, 12 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/input/keyboard/tca8418_keypad.c b/drivers/input/keyboard/tca8418_keypad.c
> index 9002298698fc..3048ef3e3e16 100644
> --- a/drivers/input/keyboard/tca8418_keypad.c
> +++ b/drivers/input/keyboard/tca8418_keypad.c
> @@ -164,11 +164,18 @@ static void tca8418_read_keypad(struct tca8418_keypad *keypad_data)
> int error, col, row;
> u8 reg, state, code;
>
> - /* Initial read of the key event FIFO */
> - error = tca8418_read_byte(keypad_data, REG_KEY_EVENT_A, ®);
> + do {
> + error = tca8418_read_byte(keypad_data, REG_KEY_EVENT_A, ®);
> + if (error < 0) {
> + dev_err(&keypad_data->client->dev,
> + "unable to read REG_KEY_EVENT_A\n");
> + break;
> + }
> +
> + /* Assume that key code 0 signifies empty FIFO */
> + if (reg <= 0)
> + break;
I am unconvinced that this rearrangement fixes the issue for all older
GCCs. Can we simply do:
u8 uninitialized_var(reg);
and be done with it?
Thanks.
--
Dmitry
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Input: tca8418_keypad: hide gcc-4.9 -Wmaybe-uninitialized warning
2016-10-24 23:45 ` Dmitry Torokhov
@ 2016-10-25 9:59 ` Arnd Bergmann
2016-10-26 22:59 ` Dmitry Torokhov
0 siblings, 1 reply; 4+ messages in thread
From: Arnd Bergmann @ 2016-10-25 9:59 UTC (permalink / raw)
To: Dmitry Torokhov; +Cc: linux-input, linux-kernel
On Monday, October 24, 2016 4:45:13 PM CEST Dmitry Torokhov wrote:
> > diff --git a/drivers/input/keyboard/tca8418_keypad.c b/drivers/input/keyboard/tca8418_keypad.c
> > index 9002298698fc..3048ef3e3e16 100644
> > --- a/drivers/input/keyboard/tca8418_keypad.c
> > +++ b/drivers/input/keyboard/tca8418_keypad.c
> > @@ -164,11 +164,18 @@ static void tca8418_read_keypad(struct tca8418_keypad *keypad_data)
> > int error, col, row;
> > u8 reg, state, code;
> >
> > - /* Initial read of the key event FIFO */
> > - error = tca8418_read_byte(keypad_data, REG_KEY_EVENT_A, ®);
> > + do {
> > + error = tca8418_read_byte(keypad_data, REG_KEY_EVENT_A, ®);
> > + if (error < 0) {
> > + dev_err(&keypad_data->client->dev,
> > + "unable to read REG_KEY_EVENT_A\n");
> > + break;
> > + }
> > +
> > + /* Assume that key code 0 signifies empty FIFO */
> > + if (reg <= 0)
> > + break;
>
> I am unconvinced that this rearrangement fixes the issue for all older
> GCCs. Can we simply do:
>
> u8 uninitialized_var(reg);
>
> and be done with it?
Yes, that would work. However:
- avoiding the fake intialization tends to produce better object
code, as gcc actually knows what's going on
- Linus doesn't like uninitialized_var() and would rather see it
removed from the kernel
- llvm produces warnings for uninitialized_var()
I have checked gcc-4.6/4.7/4.8/4.9/5.x/6.x, and only gcc-4.9
produces the warning. 4.9 changed the detection for uninitialized
variables significantly, which generally caused fewer false
positives but unfortunately introduced a couple of new ones
like this.
Arnd
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Input: tca8418_keypad: hide gcc-4.9 -Wmaybe-uninitialized warning
2016-10-25 9:59 ` Arnd Bergmann
@ 2016-10-26 22:59 ` Dmitry Torokhov
0 siblings, 0 replies; 4+ messages in thread
From: Dmitry Torokhov @ 2016-10-26 22:59 UTC (permalink / raw)
To: Arnd Bergmann; +Cc: linux-input, linux-kernel
On Tue, Oct 25, 2016 at 11:59:22AM +0200, Arnd Bergmann wrote:
> On Monday, October 24, 2016 4:45:13 PM CEST Dmitry Torokhov wrote:
> > > diff --git a/drivers/input/keyboard/tca8418_keypad.c b/drivers/input/keyboard/tca8418_keypad.c
> > > index 9002298698fc..3048ef3e3e16 100644
> > > --- a/drivers/input/keyboard/tca8418_keypad.c
> > > +++ b/drivers/input/keyboard/tca8418_keypad.c
> > > @@ -164,11 +164,18 @@ static void tca8418_read_keypad(struct tca8418_keypad *keypad_data)
> > > int error, col, row;
> > > u8 reg, state, code;
> > >
> > > - /* Initial read of the key event FIFO */
> > > - error = tca8418_read_byte(keypad_data, REG_KEY_EVENT_A, ®);
> > > + do {
> > > + error = tca8418_read_byte(keypad_data, REG_KEY_EVENT_A, ®);
> > > + if (error < 0) {
> > > + dev_err(&keypad_data->client->dev,
> > > + "unable to read REG_KEY_EVENT_A\n");
> > > + break;
> > > + }
> > > +
> > > + /* Assume that key code 0 signifies empty FIFO */
> > > + if (reg <= 0)
> > > + break;
> >
> > I am unconvinced that this rearrangement fixes the issue for all older
> > GCCs. Can we simply do:
> >
> > u8 uninitialized_var(reg);
> >
> > and be done with it?
>
> Yes, that would work. However:
>
> - avoiding the fake intialization tends to produce better object
> code, as gcc actually knows what's going on
> - Linus doesn't like uninitialized_var() and would rather see it
> removed from the kernel
> - llvm produces warnings for uninitialized_var()
>
> I have checked gcc-4.6/4.7/4.8/4.9/5.x/6.x, and only gcc-4.9
> produces the warning. 4.9 changed the detection for uninitialized
> variables significantly, which generally caused fewer false
> positives but unfortunately introduced a couple of new ones
> like this.
OK, I'll apply it then.
Thanks.
--
Dmitry
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2016-10-26 23:00 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2016-10-24 15:32 [PATCH] Input: tca8418_keypad: hide gcc-4.9 -Wmaybe-uninitialized warning Arnd Bergmann
2016-10-24 23:45 ` Dmitry Torokhov
2016-10-25 9:59 ` Arnd Bergmann
2016-10-26 22:59 ` Dmitry Torokhov
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