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,
+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
