Re: [PATCH v5 2/2] scripts: checkpatch: check unused parameters for function-like macro

[Mac Xu]

> On Tue, 2024-04-02 at 00:16 +0000, Mac Xu wrote:
> > > On Mon, 2024-04-01 at 14:21 +1300, Barry Song wrote:
> > > > From: Xining Xu <mac.xxn@xxxxxxxxxxx>
> > > >
> > > > If function-like macros do not utilize a parameter, it might result in a
> > > > build warning.  In our coding style guidelines, we advocate for utilizing
> > > > static inline functions to replace such macros.  This patch verifies
> > > > compliance with the new rule.
> > > >
> > > > For a macro such as the one below,
> > > >
> > > >  #define test(a) do { } while (0)
> > > >
> > > > The test result is as follows.
> > > >
> > > >  ERROR: Parameter 'a' is not used in function-like macro, please use static
> > > >  inline instead
> > > >  #21: FILE: mm/init-mm.c:20:
> > > >  +#define test(a) do { } while (0)
> > >
> > > This is no longer true.
> > > Please update the ERROR->WARN and message as below
> > >
> > > Ideally, this would have an update to
> > > Documentation/dev-tools/checkpatch.rst
> > >
> > > to describe the new --verbose message type
> >
> > Hi Joe,
> >
> > Thank you for the comments, here's the code:
> >
> > +# check if this is an unused argument
> > +if ($define_stmt !~ /\b$arg\b/) {
> > +     WARN("MACRO_ARG_UNUSED",
> > +             "Argument '$arg' is not used in function-like macro\n" . "$herectx");
> > +}
> >
> > and here's the document for it which is inserted into the "Macros, Attributes and
> > Symbols" section of checkpatch.rst starting from line 909:
> > +
> > +  **MACRO_ARG_UNUSED**
> > +    If function-like macros do not utilize a parameter, it might result
> > +    in a build warning. We advocate for utilizing static inline functions
> > +    to replace such macros.
> > +    For example, for a macro as below::
> > +
> > +      #define test(a) do { } while (0)
> > +
> > +    there would be a warning as below::
> > +
> > +      WARNING: Parameter 'a' is not used in function-like macro, please use
> > +      static inline instead.
> >
> > Please let me know if the document needs further re-wording to make it helpful enough
> > to the readers.
> 
> Hi again Xining.
> 
> Thanks.
> 
> That looks good but it doesn't match the script output
> which doesn't use ", please use static inline instead."
> (and I believe the script should not output that too)
> 
> Another good thing would be to add a line like:
> 
>         See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl
> 
> For example, from: checkpatch.rst
> 
>   **ALLOC_SIZEOF_STRUCT**
>     The allocation style is bad.  In general for family of
>     allocation functions using sizeof() to get memory size,
>     constructs like::
> 
>       p = alloc(sizeof(struct foo), ...)
> 
>     should be::
> 
>       p = alloc(sizeof(*p), ...)
> 
>     See: https://www.kernel.org/doc/html/latest/process/coding-style.html#allocating-memory
> 
> 

Hi again Joe,

Thanks again for the detailed comments.

Here's the code (which keeps unchanged):
+# check if this is an unused argument
+if ($define_stmt !~ /\b$arg\b/) {
+  WARN("MACRO_ARG_UNUSED",
+    "Argument '$arg' is not used in function-like macro\n" . "$herectx");
+}

And here's the updated document, which drops the ", please use static inline instead" from the
warning message, and adds a link at the end of this document block:
+
+  **MACRO_ARG_UNUSED**
+    If function-like macros do not utilize a parameter, it might result
+    in a build warning. We advocate for utilizing static inline functions
+    to replace such macros.
+    For example, for a macro such as the one below::
+
+      #define test(a) do { } while (0)
+
+    there would be a warning like below::
+
+      WARNING: Parameter 'a' is not used in function-like macro.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl


Regards,
Xining.