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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43fe4cc0f31sm59174867f8f.12.2026.04.24.04.09.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Apr 2026 04:09:51 -0700 (PDT) Date: Fri, 24 Apr 2026 12:09:43 +0100 From: David Laight To: Link Mauve Cc: "Mukesh Kumar Chaurasiya (IBM)" , maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, chleroy@kernel.org, peterz@infradead.org, jpoimboe@kernel.org, jbaron@akamai.com, aliceryhl@google.com, rostedt@goodmis.org, ardb@kernel.org, sumit.semwal@linaro.org, christian.koenig@amd.com, ojeda@kernel.org, boqun@kernel.org, gary@garyguo.net, bjorn3_gh@protonmail.com, lossin@kernel.org, a.hindborg@kernel.org, tmgross@umich.edu, dakr@kernel.org, nathan@kernel.org, nick.desaulniers+lkml@gmail.com, morbo@google.com, justinstitt@google.com, tamird@kernel.org, arnd@arndb.de, nsc@kernel.org, simona.vetter@ffwll.ch, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, rust-for-linux@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH V13 5/7] rust: Make __udivdi3() and __umoddi3() panic Message-ID: <20260424120943.4a65dd69@pumpkin> In-Reply-To: References: <20260424054742.45832-1-mkchauras@gmail.com> <20260424054742.45832-6-mkchauras@gmail.com> <20260424101425.6bde0e17@pumpkin> 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=UTF-8 Content-Transfer-Encoding: quoted-printable On Fri, 24 Apr 2026 11:43:11 +0200 Link Mauve wrote: > On Fri, Apr 24, 2026 at 10:14:25AM +0100, David Laight wrote: > > On Fri, 24 Apr 2026 11:17:40 +0530 > > "Mukesh Kumar Chaurasiya (IBM)" wrote: > > =20 > > > From: Link Mauve > > >=20 > > > The core crate currently depends on these two functions for i64/u64/ > > > i128/u128/core::time::Duration formatting, but we shouldn=E2=80=99t u= se that in > > > the kernel so let=E2=80=99s panic if they are ever called. =20 > >=20 > > Ugg. > > Surely you can make it a link-time failure? > > Or change the underlying code to avoid the divide. =20 >=20 > This is currently a link-time failure, which means if any of the core > crate or drm_panic_qr are linked in, the kernel will fail to link. >=20 > And since we rely on core, that means no kernel can be built on PowerPC > without this patch. >=20 > A possible solution would be to change the core crate to not divide > u64s, but the last time I tried to do that I couldn=E2=80=99t quite figur= e out > how to do formatting without it, maybe I will just open an issue against > Rust. If the problematic code is (effectively) printf("%lld", val) there are much better ways to generate the digit string than repeated 64bit divides. On particular you can use 'multiply by reciprocal' instead. For example see the latest (I think it'll be in 7.1-rc) version of tools/include/nolibc/stdlib.h David