Re: [PATCH v2] staging/comedi/dt282x: avoid integer overflow warning

2016-03-19 Thread Arnd Bergmann 
On Thursday 17 March 2016 15:47:57 Hartley Sweeten wrote:
> On Wednesday, March 16, 2016 1:51 PM, Arnd Bergmann wrote:
> 
> Is this a gcc-6 specific issue? Seems line this warning should be showing
> up in a lot of drivers.

Yes, I did not see this before moving to gcc-6.0, but this is the only driver
I've encountered the warning for, in around 7000 randconfig builds.

> > The warning makes sense, though the code is correct as far as I
> > can tell.
> >
> > This disambiguates the operation by making the constant expressions
> > we pass here explicitly 'unsigned', which helps to avoid the warning.
> >
> > As pointed out by Hartley Sweeten, scripts/checkpatch.pl notices that
> > the shifts here are rather unreadable, though the suggested BIT()
> > macro wouldn't work either. I'm changing it to a hexadecimal notation,
> > which hopefully improves readability. I'm leaving the DT2821_CHANCSR_PRESLA
> > alone because it seems wrong.
> 
> BIT() should work for the ones pointed out by checpatch.pl.
> 
> I would argue that the hexadecimal notation is still rather unreadable.
> These ones make my head hurt...
> 
> -#define DT2821_ADCSR_GS(x)   (((x) & 0x3) << 4)
> +#define DT2821_ADCSR_GS(x)  (0x0030u & ((x) << 4))
> 
> -#define DT2821_DACSR_YSEL(x) ((x) << 9)
> +#define DT2821_DACSR_YSEL(x)(0x7e00u & (x) << 9)
> 
> -#define DT2821_SUPCSR_DS_PIO (0 << 10)
> -#define DT2821_SUPCSR_DS_AD_CLK  (1 << 10)
> -#define DT2821_SUPCSR_DS_DA_CLK  (2 << 10)
> -#define DT2821_SUPCSR_DS_AD_TRIG (3 << 10)
> +#define DT2821_SUPCSR_DS_PIO(0x0c00u & (0u << 10))
> +#define DT2821_SUPCSR_DS_AD_CLK (0x0c00u & (1u << 10))
> +#define DT2821_SUPCSR_DS_DA_CLK (0x0c00u & (2u << 10))
> +#define DT2821_SUPCSR_DS_AD_TRIG   (0x0c00u & (3u << 10))

Feel free to come up with a different patch. I've put the patch on
my 'submitted' stack for now and will get back to it after 4.7-rc1 if
the warning remains.

> Also, most of the comedi drivers use the BIT() macro. Are you planning on
> changing all of them to use hexadecimal notation?

No.

Arnd
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RE: [PATCH v2] staging/comedi/dt282x: avoid integer overflow warning

2016-03-19 Thread Hartley Sweeten 
On Thursday, March 17, 2016 9:09 AM, Arnd Bergmann wrote:
> On Thursday 17 March 2016 15:47:57 Hartley Sweeten wrote:
>> On Wednesday, March 16, 2016 1:51 PM, Arnd Bergmann wrote:
>> 
>> Is this a gcc-6 specific issue? Seems line this warning should be showing
>> up in a lot of drivers.
>
> Yes, I did not see this before moving to gcc-6.0, but this is the only driver
> I've encountered the warning for, in around 7000 randconfig builds.

Weird...

> Feel free to come up with a different patch. I've put the patch on
> my 'submitted' stack for now and will get back to it after 4.7-rc1 if
> the warning remains.

I'll post an alternate patch shortly that is more consistent with the
other comedi drivers.

If you could test that it fixes the gcc-6 issue that would be great!

Thanks,
Hartley

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Re: [PATCH v2] staging/comedi/dt282x: avoid integer overflow warning

2016-03-19 Thread Ian Abbott 

On 16/03/16 20:51, Arnd Bergmann wrote:

gcc-6 warns about passing negative signed integer into swab16()
in the dt282x driver:

drivers/staging/comedi/drivers/dt282x.c: In function 'dt282x_load_changain':
include/uapi/linux/swab.h:14:33: warning: integer overflow in expression 
[-Woverflow]
   (((__u16)(x) & (__u16)0xff00U) >> 8)))
   ~~~^
include/uapi/linux/swab.h:107:2: note: in expansion of macro 
'___constant_swab16'
   ___constant_swab16(x) :   \
   ^~
include/uapi/linux/byteorder/big_endian.h:34:43: note: in expansion of macro 
'__swab16'
  #define __cpu_to_le16(x) ((__force __le16)__swab16((x)))
^~~~
include/linux/byteorder/generic.h:89:21: note: in expansion of macro 
'__cpu_to_le16'
  #define cpu_to_le16 __cpu_to_le16
  ^
arch/arm/include/asm/io.h:250:6: note: in expansion of macro 'cpu_to_le16'
   cpu_to_le16(v),__io(p)); })
   ^~~
drivers/staging/comedi/drivers/dt282x.c:566:2: note: in expansion of macro 
'outw'
   outw(DT2821_CHANCSR_LLE | DT2821_CHANCSR_NUMB(n),
   ^~~~

The warning makes sense, though the code is correct as far as I
can tell.

This disambiguates the operation by making the constant expressions
we pass here explicitly 'unsigned', which helps to avoid the warning.

As pointed out by Hartley Sweeten, scripts/checkpatch.pl notices that
the shifts here are rather unreadable, though the suggested BIT()
macro wouldn't work either. I'm changing it to a hexadecimal notation,
which hopefully improves readability. I'm leaving the DT2821_CHANCSR_PRESLA
alone because it seems wrong.

Signed-off-by: Arnd Bergmann 
---
v2: also reformat to make checkpatch.pl happy

  drivers/staging/comedi/drivers/dt282x.c | 72 -
  1 file changed, 36 insertions(+), 36 deletions(-)

diff --git a/drivers/staging/comedi/drivers/dt282x.c 
b/drivers/staging/comedi/drivers/dt282x.c

[snip]

-#define DT2821_CHANCSR_LLE (1 << 15)
-#define DT2821_CHANCSR_PRESLA(x)   (((x) & 0xf) >> 8)
-#define DT2821_CHANCSR_NUMB(x) x) - 1) & 0xf) << 0)
+#define DT2821_CHANCSR_LLE 0x8000u
+#define DT2821_CHANCSR_PRESLA(x)   (((x) & 0xf) >> 8) /* always 0? */


The patch is fine, thanks.

Just a note on that dodgy-looking '>>' in the DT2821_CHANCSR_PRESLA 
macro I seems to be a typo in 0f8e8c5ab67a ("staging: comedi: 
dt282x: tidy up the register map and bit defines").  It should be a 
left-shift.  Fortunately, it isn't used, but we ought to correct it 
sometime.


Reviewed-by: Ian Abbott 

--
-=( Ian Abbott @ MEV Ltd.E-mail:  )=-
-=(  Web: http://www.mev.co.uk/  )=-
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RE: [PATCH v2] staging/comedi/dt282x: avoid integer overflow warning

2016-03-19 Thread Hartley Sweeten 
On Wednesday, March 16, 2016 1:51 PM, Arnd Bergmann wrote:
>
> gcc-6 warns about passing negative signed integer into swab16()
> in the dt282x driver:
>
> drivers/staging/comedi/drivers/dt282x.c: In function 'dt282x_load_changain':
> include/uapi/linux/swab.h:14:33: warning: integer overflow in expression 
> [-Woverflow]
>   (((__u16)(x) & (__u16)0xff00U) >> 8)))
>   ~~~^
> include/uapi/linux/swab.h:107:2: note: in expansion of macro 
> '___constant_swab16'
>   ___constant_swab16(x) :   \
>   ^~
> include/uapi/linux/byteorder/big_endian.h:34:43: note: in expansion of macro 
> '__swab16'
>  #define __cpu_to_le16(x) ((__force __le16)__swab16((x)))
>^~~~
> include/linux/byteorder/generic.h:89:21: note: in expansion of macro 
> '__cpu_to_le16'
>  #define cpu_to_le16 __cpu_to_le16
>  ^
> arch/arm/include/asm/io.h:250:6: note: in expansion of macro 'cpu_to_le16'
>   cpu_to_le16(v),__io(p)); })
>   ^~~
> drivers/staging/comedi/drivers/dt282x.c:566:2: note: in expansion of macro 
> 'outw'
>   outw(DT2821_CHANCSR_LLE | DT2821_CHANCSR_NUMB(n),
>   ^~~~

Arnd,

Is this a gcc-6 specific issue? Seems line this warning should be showing
up in a lot of drivers.

> The warning makes sense, though the code is correct as far as I
> can tell.
>
> This disambiguates the operation by making the constant expressions
> we pass here explicitly 'unsigned', which helps to avoid the warning.
>
> As pointed out by Hartley Sweeten, scripts/checkpatch.pl notices that
> the shifts here are rather unreadable, though the suggested BIT()
> macro wouldn't work either. I'm changing it to a hexadecimal notation,
> which hopefully improves readability. I'm leaving the DT2821_CHANCSR_PRESLA
> alone because it seems wrong.

BIT() should work for the ones pointed out by checpatch.pl.

I would argue that the hexadecimal notation is still rather unreadable.
These ones make my head hurt...

-#define DT2821_ADCSR_GS(x) (((x) & 0x3) << 4)
+#define DT2821_ADCSR_GS(x)(0x0030u & ((x) << 4))

-#define DT2821_DACSR_YSEL(x)   ((x) << 9)
+#define DT2821_DACSR_YSEL(x)  (0x7e00u & (x) << 9)

-#define DT2821_SUPCSR_DS_PIO   (0 << 10)
-#define DT2821_SUPCSR_DS_AD_CLK(1 << 10)
-#define DT2821_SUPCSR_DS_DA_CLK(2 << 10)
-#define DT2821_SUPCSR_DS_AD_TRIG   (3 << 10)
+#define DT2821_SUPCSR_DS_PIO  (0x0c00u & (0u << 10))
+#define DT2821_SUPCSR_DS_AD_CLK   (0x0c00u & (1u << 10))
+#define DT2821_SUPCSR_DS_DA_CLK   (0x0c00u & (2u << 10))
+#define DT2821_SUPCSR_DS_AD_TRIG   (0x0c00u & (3u << 10))

Also, most of the comedi drivers use the BIT() macro. Are you planning on
changing all of them to use hexadecimal notation?

Regards,
Hartley

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