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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43656af6aeesm85758955e9.6.2024.12.20.09.29.21 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Fri, 20 Dec 2024 09:29:21 -0800 (PST) Date: Fri, 20 Dec 2024 17:29:20 +0000 From: David Laight To: Guenter Roeck Cc: kernel test robot , Eddie James , oe-kbuild-all@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: drivers/hwmon/pmbus/ibm-cffps.c:184:60: warning: '%04X' directive output may be truncated writing between 4 and 8 bytes into a region of size 5 Message-ID: <20241220172920.7a34eb46@dsl-u17-10> In-Reply-To: References: <202412202139.tZ2VJL2f-lkp@intel.com> <20241220163056.7bad4962@dsl-u17-10> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 20 Dec 2024 09:03:51 -0800 Guenter Roeck wrote: > On 12/20/24 08:30, David Laight wrote: ... > >> > >>> drivers/hwmon/pmbus/ibm-cffps.c:171:60: warning: '%02X' directive output may be truncated writing between 2 and 8 bytes into a region of size 3 [-Wformat-truncation=] > >>> 171 | snprintf(&data[i * 2], 3, "%02X", rc); > > > > The only ways I know are to bound check the value or to use > > OPTIMISER_HIDE_VAR() on the length. > > > > - snprintf(&data[i * 2], 3, "%02X", rc); > + snprintf(&data[i * 2], 3, "%02X", rc & 0xff); > > works as well, at least with gcc 11 and 12, but I really dislike that kind of nonsense. Ditto. Using the result in some ways can also remove the warning. But you have to try quite hard, a simple (void) really ought to be enough to show you 'just don't care' but even 'if (snprintf(...)) {}' isn't enough (it does silence 'warn-unused-result'). I mean, the whole point of snprintf() is that it truncates. David