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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4856ea97e8esm74472665e9.5.2026.03.17.07.56.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Mar 2026 07:56:48 -0700 (PDT) Date: Tue, 17 Mar 2026 14:56:47 +0000 From: David Laight To: "Arnd Bergmann" Cc: "Matt Roper" , "Arnd Bergmann" , "Matthew Brost" , Thomas =?UTF-8?B?SGVsbHN0csO2bQ==?= , "Rodrigo Vivi" , "Dave Airlie" , "Simona Vetter" , "Dnyaneshwar Bhadane" , "Lucas De Marchi" , "Tvrtko Ursulin" , "Umesh Nerlige Ramappa" , "Raag Jadav" , "Niranjana Vishwanathapura" , intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] drm/xe: use %z format string for ptrdiff_t Message-ID: <20260317145647.0d5de2a1@pumpkin> In-Reply-To: References: <20260316224357.658520-1-arnd@kernel.org> <20260316225118.GD2729713@mdroper-desk1.amr.corp.intel.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) 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 Tue, 17 Mar 2026 00:07:57 +0100 "Arnd Bergmann" wrote: > On Mon, Mar 16, 2026, at 23:51, Matt Roper wrote: > > On Mon, Mar 16, 2026 at 11:43:46PM +0100, Arnd Bergmann wrote: > >> From: Arnd Bergmann > >> > >> ptrdiff_t, size_t and long are the same size on all supported architectures, > >> but gcc requires the use of the %zx modifier instead of %lx. On 32-bit > > > > Nathan Chancellor just sent a fix here: > > > > https://lore.kernel.org/all/20260316-drm-xe-fix-32-bit-wformat-ptrdiff-v1-1-0108b10b2b6b@kernel.org/ > > > > His solution uses %tx rather than %zx, which according to > > Documentation/core-api/printk-formats.rst sounds like it's probably the > > most accurate format string for this case? > > > > Right, Nathan's version is correct. I wasn't aware that size_t > and ptrdiff_t have different modifiers. Consider: void foo(size_t len) { char *p = malloc(len); char *end = p + len; ptrdiff_t diff = p - end; printf("len %zu, diff %td\n", len, diff); free(p); } Clearly foo(5) output "5 -5". But what about foo(5u << 29) on a 32bit system with a large unlimit and a big enough hole in the address space. More likely would be something running on an x86 in real mode. There malloc(65000) might be reasonable, so size_t would be unsigned int but ptrdiff_t would need to be a signed 32bit type. Of course, in linux, they are all 'long'. David > > Arnd >