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Tue, 19 Mar 2024 17:17:13 -0700 (PDT) Received: from localhost.localdomain ([2407:7000:8942:5500:aaa1:59ff:fe57:eb97]) by smtp.gmail.com with ESMTPSA id ks11-20020a056a004b8b00b006e647059cccsm10357007pfb.33.2024.03.19.17.17.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Mar 2024 17:17:13 -0700 (PDT) From: Barry Song <21cnbao@gmail.com> To: corbet@lwn.net, workflows@vger.kernel.org, linux-doc@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Barry Song , Andrew Morton , Chris Zankel , Huacai Chen , Herbert Xu , Guenter Roeck , Max Filippov Subject: [PATCH] Documentation: coding-style: ask function-like macros to evaluate parameters Date: Wed, 20 Mar 2024 13:16:56 +1300 Message-Id: <20240320001656.10075-1-21cnbao@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: workflows@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Barry Song 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 Cc: Chris Zankel Cc: Huacai Chen Cc: Herbert Xu Cc: Guenter Roeck Suggested-by: Max Filippov Signed-off-by: Barry Song --- 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