> On Mar 20, 2024, at 08:17, Barry Song <21cnbao@xxxxxxxxx> wrote:
>
> From: Barry Song <v-songbaohua@xxxxxxxx>
>
> Recent commit 77292bb8ca69c80 ("crypto: scomp - remove memcpy if
> sg_nents is 1 and pages are lowmem") leads to warnings on xtensa
> and loongarch,
> In file included from crypto/scompress.c:12:
> include/crypto/scatterwalk.h: In function 'scatterwalk_pagedone':
> include/crypto/scatterwalk.h:76:30: warning: variable 'page' set but not used [-Wunused-but-set-variable]
> 76 | struct page *page;
> | ^~~~
> crypto/scompress.c: In function 'scomp_acomp_comp_decomp':
>>> crypto/scompress.c:174:38: warning: unused variable 'dst_page' [-Wunused-variable]
> 174 | struct page *dst_page = sg_page(req->dst);
> |
>
> The reason is that flush_dcache_page() is implemented as a noop
> macro on these platforms as below,
>
> #define flush_dcache_page(page) do { } while (0)
>
> The driver code, for itself, seems be quite innocent and placing
> maybe_unused seems pointless,
>
> struct page *dst_page = sg_page(req->dst);
>
> for (i = 0; i < nr_pages; i++)
> flush_dcache_page(dst_page + i);
>
> And it should be independent of architectural implementation
> differences.
>
> Let's have a guidance in codingstyle to ask for the evaluation
> of parameters.
>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Chris Zankel <chris@xxxxxxxxxx>
> Cc: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
> Suggested-by: Max Filippov <jcmvbkbc@xxxxxxxxx>
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> ---
> Documentation/process/coding-style.rst | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst
> index 9c7cf7347394..8065747fddff 100644
> --- a/Documentation/process/coding-style.rst
> +++ b/Documentation/process/coding-style.rst
> @@ -827,6 +827,13 @@ Macros with multiple statements should be enclosed in a do - while block:
> do_this(b, c); \
> } while (0)
>
> +Function-like macros should evaluate their parameters, for unused parameters,
I do not support this point, if the parameter is unused, why not to remove it.
about the warning, is tool misreport, the tool must make better
> +cast them to void:
> +
> +.. code-block:: c
> +
> + #define macrofun(a) do { (void) (a); } while (0)
> +
> Things to avoid when using macros:
>
> 1) macros that affect control flow:
> --
> 2.34.1
>
