From: Andrew Morton <akpm@linux-foundation.org>
To: mm-commits@vger.kernel.org,sfr@canb.auug.org.au,quic_jjohnson@quicinc.com,mac.xxn@outlook.com,lukas.bulwahn@gmail.com,linux@roeck-us.net,joe@perches.com,jcmvbkbc@gmail.com,herbert@gondor.apana.org.au,dwaipayanray1@gmail.com,corbet@lwn.net,chris@zankel.net,chenhuacai@loongson.cn,charlemagnelasse@gmail.com,broonie@kernel.org,apw@canonical.com,v-songbaohua@oppo.com,akpm@linux-foundation.org
Subject: + documentation-coding-style-ask-function-like-macros-to-evaluate-parameters.patch added to mm-nonmm-unstable branch
Date: Tue, 07 May 2024 10:24:27 -0700 [thread overview]
Message-ID: <20240507172428.1EC98C4AF18@smtp.kernel.org> (raw)
The patch titled
Subject: Documentation: coding-style: ask function-like macros to evaluate parameters
has been added to the -mm mm-nonmm-unstable branch. Its filename is
documentation-coding-style-ask-function-like-macros-to-evaluate-parameters.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/documentation-coding-style-ask-function-like-macros-to-evaluate-parameters.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Barry Song <v-songbaohua@oppo.com>
Subject: Documentation: coding-style: ask function-like macros to evaluate parameters
Date: Tue, 7 May 2024 15:27:56 +1200
Patch series "codingstyle: avoid unused parameters for a function-like
macro", v7.
A function-like macro could result in build warnings such as "unused
variable." This patchset updates the guidance to recommend always using a
static inline function instead and also provides checkpatch support for
this new rule.
This patch (of 2):
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.
Link: https://lkml.kernel.org/r/20240507032757.146386-1-21cnbao@gmail.com
Link: https://lkml.kernel.org/r/20240507032757.146386-2-21cnbao@gmail.com
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Suggested-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Joe Perches <joe@perches.com>
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>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Xining Xu <mac.xxn@outlook.com>
Cc: Charlemagne Lasse <charlemagnelasse@gmail.com>
Cc: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
Documentation/process/coding-style.rst | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
--- a/Documentation/process/coding-style.rst~documentation-coding-style-ask-function-like-macros-to-evaluate-parameters
+++ a/Documentation/process/coding-style.rst
@@ -827,6 +827,29 @@ Macros with multiple statements should b
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:
_
Patches currently in -mm which might be from v-songbaohua@oppo.com are
mailmap-add-entry-for-barry-song.patch
documentation-coding-style-ask-function-like-macros-to-evaluate-parameters.patch
next reply other threads:[~2024-05-07 17:24 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-07 17:24 Andrew Morton [this message]
-- strict thread matches above, loose matches on Subject: below --
2024-03-22 19:06 + documentation-coding-style-ask-function-like-macros-to-evaluate-parameters.patch added to mm-nonmm-unstable branch Andrew Morton
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