From: Barry Song <v-songbao...@oppo.com>
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 provide guidance on coding style for requesting parameter
evaluation or proposing the migration to a static inline
function.
Signed-off-by: Barry Song <v-songbao...@oppo.com>
Suggested-by: Max Filippov <jcmvb...@gmail.com>
Reviewed-by: Mark Brown <broo...@kernel.org>
Acked-by: Joe Perches <j...@perches.com>
Cc: Chris Zankel <ch...@zankel.net>
Cc: Huacai Chen <chenhua...@loongson.cn>
Cc: Herbert Xu <herb...@gondor.apana.org.au>
Cc: Guenter Roeck <li...@roeck-us.net>
Cc: Stephen Rothwell <s...@canb.auug.org.au>
Cc: Andy Whitcroft <a...@canonical.com>
Cc: Dwaipayan Ray <dwaipayanr...@gmail.com>
Cc: Joe Perches <j...@perches.com>
Cc: Jonathan Corbet <cor...@lwn.net>
Cc: Lukas Bulwahn <lukas.bulw...@gmail.com>
Cc: Xining Xu <mac....@outlook.com>
---
Documentation/process/coding-style.rst | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/Documentation/process/coding-style.rst
b/Documentation/process/coding-style.rst
index 9c7cf7347394..7e768c65aa92 100644
--- a/Documentation/process/coding-style.rst
+++ b/Documentation/process/coding-style.rst
@@ -827,6 +827,29 @@ Macros with multiple statements should be enclosed in a do
- while block:
do_this(b, c); \
} while (0)
+Function-like macros with unused parameters should be replaced by static
+inline functions to avoid the issue of unused variables:
+
+.. code-block:: c
+
+ static inline void fun(struct foo *foo)
+ {
+ }
+
+Due to historical practices, many files still employ the "cast to (void)"
+approach to evaluate parameters. However, this method is not advisable.
+Inline functions address the issue of "expression with side effects
+evaluated more than once", circumvent unused-variable problems, and
+are generally better documented than macros for some reason.
+
+.. code-block:: c
+
+ /*
+ * Avoid doing this whenever possible and instead opt for static
+ * inline functions
+ */
+ #define macrofun(foo) do { (void) (foo); } while (0)
+
Things to avoid when using macros:
1) macros that affect control flow:
--
2.34.1
