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 Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** 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 and is updated there every 2-3 working days ------------------------------------------------------ From: Barry Song <v-songbaohua@xxxxxxxx> Subject: Documentation: coding-style: ask function-like macros to evaluate parameters Date: Fri, 22 Mar 2024 21:49:36 +1300 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/20240322084937.66018-2-21cnbao@xxxxxxxxx Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx> Suggested-by: Max Filippov <jcmvbkbc@xxxxxxxxx> Reviewed-by: Mark Brown <broonie@xxxxxxxxxx> Cc: Chris Zankel <chris@xxxxxxxxxx> Cc: Huacai Chen <chenhuacai@xxxxxxxxxxx> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Cc: Guenter Roeck <linux@xxxxxxxxxxxx> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Cc: Andy Whitcroft <apw@xxxxxxxxxxxxx> Cc: Dwaipayan Ray <dwaipayanray1@xxxxxxxxx> Cc: Joe Perches <joe@xxxxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx> Cc: Xining Xu <ma.xxn@xxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/process/coding-style.rst | 16 ++++++++++++++++ 1 file changed, 16 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 +827,22 @@ 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) + { + } + +For historical reasons, many files still use the cast to (void) to evaluate +parameters, but this method is not recommended: + +.. code-block:: c + + #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@xxxxxxxx are mm-zswap-fix-kernel-bug-in-sg_init_one.patch arm64-mm-swap-support-thp_swap-on-hardware-with-mte.patch documentation-coding-style-ask-function-like-macros-to-evaluate-parameters.patch