From: Barry Song <21cnbao@gmail.com>
To: corbet@lwn.net, workflows@vger.kernel.org,
linux-doc@vger.kernel.org, sfr@canb.auug.org.au
Cc: linux-kernel@vger.kernel.org, Barry Song <v-songbaohua@oppo.com>,
Andrew Morton <akpm@linux-foundation.org>,
Chris Zankel <chris@zankel.net>,
Huacai Chen <chenhuacai@loongson.cn>,
Herbert Xu <herbert@gondor.apana.org.au>,
Guenter Roeck <linux@roeck-us.net>,
Max Filippov <jcmvbkbc@gmail.com>
Subject: [PATCH v2] Documentation: coding-style: ask function-like macros to evaluate parameters
Date: Wed, 20 Mar 2024 17:47:28 +1300 [thread overview]
Message-ID: <20240320044728.20313-1-21cnbao@gmail.com> (raw)
From: Barry Song <v-songbaohua@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.
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: Huacai Chen <chenhuacai@loongson.cn>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Guenter Roeck <linux@roeck-us.net>
Suggested-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
-v2:
* add comment about the approach of using a static inline func,
thanks for Stephen's comment
Documentation/process/coding-style.rst | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst
index 9c7cf7347394..9e0507af6253 100644
--- a/Documentation/process/coding-style.rst
+++ b/Documentation/process/coding-style.rst
@@ -827,6 +827,22 @@ 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)
+
+Another approach could involve utilizing a static inline function to replace
+the macro:
+
+.. code-block:: c
+
+ static inline void fun(struct foo *foo)
+ {
+ }
+
Things to avoid when using macros:
1) macros that affect control flow:
--
2.34.1
reply other threads:[~2024-03-20 4:47 UTC|newest]
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