[PATCH v2 1/1] scripts/coccinelle: use BIT macro if used

[PATCH v2 1/1] scripts/coccinelle: use BIT macro if used

[Javier Martinez Canillas]

Using the BIT() macro instead of manually shifting bits
makes the code less error prone.

If is more readable is a matter of taste so only replace
if the file is already using this macro.

Signed-off-by: Javier Martinez Canillas <javier@dowhile0.org>
---

Changes since v1:
 - Add a rule that checks if the file is already using this macro
   as suggested by Julia Lawall

 scripts/coccinelle/api/bit.cocci | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 scripts/coccinelle/api/bit.cocci

diff --git a/scripts/coccinelle/api/bit.cocci b/scripts/coccinelle/api/bit.cocci
new file mode 100644
index 0000000..a02cfd3
--- /dev/null
+++ b/scripts/coccinelle/api/bit.cocci
@@ -0,0 +1,30 @@
+// Use the BIT() macro if is already used
+//
+// Confidence: High
+// Copyright (C) 2014 Javier Martinez Canillas.  GPLv2.
+// URL: http://coccinelle.lip6.fr/
+// Options: --include-headers
+
+@hasbitops@
+@@
+
+#include <linux/bitops.h>
+
+@usesbit@
+@@
+
+BIT(...)
+
+@depends on hasbitops && usesbit@
+expression E;
+@@
+
+- 1 << E
++ BIT(E)
+
+@depends on hasbitops && usesbit@
+expression E;
+@@
+
+- BIT((E))
++ BIT(E)
-- 
1.9.1

Re: [Cocci] [PATCH v2 1/1] scripts/coccinelle: use BIT macro if used

[Lars-Peter Clausen]

On 04/27/2014 12:50 PM, Javier Martinez Canillas wrote:
> Using the BIT() macro instead of manually shifting bits
> makes the code less error prone.
>
> If is more readable is a matter of taste so only replace
> if the file is already using this macro.
>
> Signed-off-by: Javier Martinez Canillas <javier@dowhile0.org>

I don't think this should be enabled by default. It will generate a ton of 
false positives, not everything that is 1 shifted by something is a 
single-bit field. E.g. imagine a device with multi-bit fields:

#define FOOBAR_A (0 << FOOBAR_OFFSET)
#define FOOBAR_B (1 << FOOBAR_OFFSET)
#define FOOBAR_C (2 << FOOBAR_OFFSET)
#define FOOBAR_D (3 << FOOBAR_OFFSET)

The script will now suggest to replace FOOBAR_B (1 << FOOBAR_OFFSET) with 
FOOBAR_B BIT(FOOBAR_OFFSET). Which is technically correct, but not semantically.

- Lars

> ---
>
> Changes since v1:
>   - Add a rule that checks if the file is already using this macro
>     as suggested by Julia Lawall
>
>   scripts/coccinelle/api/bit.cocci | 30 ++++++++++++++++++++++++++++++
>   1 file changed, 30 insertions(+)
>   create mode 100644 scripts/coccinelle/api/bit.cocci
>
> diff --git a/scripts/coccinelle/api/bit.cocci b/scripts/coccinelle/api/bit.cocci
> new file mode 100644
> index 0000000..a02cfd3
> --- /dev/null
> +++ b/scripts/coccinelle/api/bit.cocci
> @@ -0,0 +1,30 @@
> +// Use the BIT() macro if is already used
> +//
> +// Confidence: High
> +// Copyright (C) 2014 Javier Martinez Canillas.  GPLv2.
> +// URL: http://coccinelle.lip6.fr/
> +// Options: --include-headers
> +
> +@hasbitops@
> +@@
> +
> +#include <linux/bitops.h>
> +
> +@usesbit@
> +@@
> +
> +BIT(...)
> +
> +@depends on hasbitops && usesbit@
> +expression E;
> +@@
> +
> +- 1 << E
> ++ BIT(E)
> +
> +@depends on hasbitops && usesbit@
> +expression E;
> +@@
> +
> +- BIT((E))
> ++ BIT(E)
>

Re: [Cocci] [PATCH v2 1/1] scripts/coccinelle: use BIT macro if used

[Javier Martinez Canillas]

Hello Lars,

On Tue, Apr 29, 2014 at 6:18 PM, Lars-Peter Clausen <lars@metafoo.de> wrote:
> On 04/27/2014 12:50 PM, Javier Martinez Canillas wrote:
>>
>> Using the BIT() macro instead of manually shifting bits
>> makes the code less error prone.
>>
>> If is more readable is a matter of taste so only replace
>> if the file is already using this macro.
>>
>> Signed-off-by: Javier Martinez Canillas <javier@dowhile0.org>
>
>
> I don't think this should be enabled by default. It will generate a ton of
> false positives, not everything that is 1 shifted by something is a
> single-bit field. E.g. imagine a device with multi-bit fields:
>
> #define FOOBAR_A (0 << FOOBAR_OFFSET)
> #define FOOBAR_B (1 << FOOBAR_OFFSET)
> #define FOOBAR_C (2 << FOOBAR_OFFSET)
> #define FOOBAR_D (3 << FOOBAR_OFFSET)
>
> The script will now suggest to replace FOOBAR_B (1 << FOOBAR_OFFSET) with
> FOOBAR_B BIT(FOOBAR_OFFSET). Which is technically correct, but not
> semantically.
>
> - Lars
>
>

Thanks a lot for your feedback. You are complete right that this is
hard to generalize so is better to just drop this patch.

I'll just continue it keeping it on my tree since I find it useful.

Best regards,
Javier