[PATCH v4] doc/checkpatch: Add description to MACRO_ARG_REUSE

[PATCH v4] doc/checkpatch: Add description to MACRO_ARG_REUSE

[Martin Fernandez]

Add a description, an example and a couple of options when it is safe
to ignore it.

Signed-off-by: Martin Fernandez <martin.fernandez@eclypsium.com>
---
 Documentation/dev-tools/checkpatch.rst | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
index c3389c6f3838..678c1956468b 100644
--- a/Documentation/dev-tools/checkpatch.rst
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -854,6 +854,32 @@ Macros, Attributes and Symbols
               ...
       }

+  **MACRO_ARG_REUSE**
+    Using the same argument multiple times in the macro definition
+    may lead to unwanted side effects.
+
+    For example, given a min() macro defined like::
+
+      #define min(x, y)  ((x) < (y) ? (x) : (y))
+
+    If you call it with ``min(foo(x), 0)``, it would expand to::
+
+      foo(x) < 0 ? foo(x) : 0
+
+    If foo has side effects or it's an expensive calculation the
+    results might not be what the user intended.
+
+    When it's safe to ignore:
+
+    - If the macro arguments of all uses of this macro are free of
+      unintended side effects. Passing a constant value is usually
+      fine, as the compiler will use constant propagation and further
+      optimizations to produce acceptable code.
+
+    - If you defined local variables that will hold the value of each
+      argument in the macro's definition. See the min() macro in
+      include/linux/minmax.h for example.
+
   **MISPLACED_INIT**
     It is possible to use section markers on variables in a way
     which gcc doesn't understand (or at least not the way the
--
2.30.2

Re: [PATCH v4] doc/checkpatch: Add description to MACRO_ARG_REUSE

[Martin Fernandez]

On 10/12/22, Martin Fernandez <martin.fernandez@eclypsium.com> wrote:
> Add a description, an example and a couple of options when it is safe
> to ignore it.
>
> Signed-off-by: Martin Fernandez <martin.fernandez@eclypsium.com>
> ---
>  Documentation/dev-tools/checkpatch.rst | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
>
> diff --git a/Documentation/dev-tools/checkpatch.rst
> b/Documentation/dev-tools/checkpatch.rst
> index c3389c6f3838..678c1956468b 100644
> --- a/Documentation/dev-tools/checkpatch.rst
> +++ b/Documentation/dev-tools/checkpatch.rst
> @@ -854,6 +854,32 @@ Macros, Attributes and Symbols
>                ...
>        }
>
> +  **MACRO_ARG_REUSE**
> +    Using the same argument multiple times in the macro definition
> +    may lead to unwanted side effects.
> +
> +    For example, given a min() macro defined like::
> +
> +      #define min(x, y)  ((x) < (y) ? (x) : (y))
> +
> +    If you call it with ``min(foo(x), 0)``, it would expand to::
> +
> +      foo(x) < 0 ? foo(x) : 0
> +
> +    If foo has side effects or it's an expensive calculation the
> +    results might not be what the user intended.
> +
> +    When it's safe to ignore:
> +
> +    - If the macro arguments of all uses of this macro are free of
> +      unintended side effects. Passing a constant value is usually
> +      fine, as the compiler will use constant propagation and further
> +      optimizations to produce acceptable code.
> +
> +    - If you defined local variables that will hold the value of each
> +      argument in the macro's definition. See the min() macro in
> +      include/linux/minmax.h for example.
> +
>    **MISPLACED_INIT**
>      It is possible to use section markers on variables in a way
>      which gcc doesn't understand (or at least not the way the
> --
> 2.30.2
>
>

Sending it again since I've got no response