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quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Fri, 21 Nov 2025 22:41:46 +0900 Message-Id: Cc: "kernel test robot" , , Subject: Re: [linux-next:master 9676/10599] ld.lld: error: undefined symbol: rust_build_error From: "Alexandre Courbot" To: "Alice Ryhl" , "Alexandre Courbot" , "Miguel Ojeda" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <202511210055.RUsFNku1-lkp@intel.com> In-Reply-To: X-ClientProxiedBy: TYCPR01CA0156.jpnprd01.prod.outlook.com (2603:1096:400:2b1::16) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|SJ0PR12MB6904:EE_ X-MS-Office365-Filtering-Correlation-Id: 2379e3e6-1b3e-4e4d-732c-08de2903b8dc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|10070799003|1800799024|376014; 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Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: G0Sor//rZ93QNxVIeoBxd5QXx/LiL70g6T2Q9M2SUanSwdDj8J+WOi9hn1uK75JD+3VrWUVsVklIDtB8mDqOPg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR12MB6904 On Fri Nov 21, 2025 at 6:08 PM JST, Alice Ryhl wrote: > On Fri, Nov 21, 2025 at 03:13:16PM +0900, Alexandre Courbot wrote: >> On Fri Nov 21, 2025 at 1:41 AM JST, kernel test robot wrote: >> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-nex= t.git master >> > head: 88cbd8ac379cf5ce68b7efcfd4d1484a6871ee0b >> > commit: 01e345e82ec3a5a7edeb9fa0dcb7fd4b0e5c534e [9676/10599] rust: nu= m: add Bounded integer wrapping type >> > config: loongarch-randconfig-6002-20251120 (https://download.01.org/0d= ay-ci/archive/20251121/202511210055.RUsFNku1-lkp@intel.com/config) >> > compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3= b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff) >> > rustc: rustc 1.88.0 (6b00bc388 2025-06-23) >> > reproduce (this is a W=3D1 build): (https://download.01.org/0day-ci/ar= chive/20251121/202511210055.RUsFNku1-lkp@intel.com/reproduce) >> > >> > If you fix the issue in a separate patch/commit (i.e. not just a new v= ersion of >> > the same patch/commit), kindly add following tags >> > | Reported-by: kernel test robot >> > | Closes: https://lore.kernel.org/oe-kbuild-all/202511210055.RUsFNku1-= lkp@intel.com/ >> > >> > All errors (new ones prefixed by >>): >> > >> >>> ld.lld: error: undefined symbol: rust_build_error >> > >>> referenced by build_assert.rs:83 (rust/kernel/build_assert.rs:8= 3) >> > >>> rust/doctests_kernel_generated.o:(>::from_expr) in archive vmlinux.a >> > >>> referenced by build_assert.rs:83 (rust/kernel/build_assert.rs:8= 3) >> > >>> rust/doctests_kernel_generated.o:(>::from_expr) in archive vmlinux.a >> > >>> referenced by build_assert.rs:83 (rust/kernel/build_assert.rs:8= 3) >> > >>> rust/doctests_kernel_generated.o:(>::from_expr) in archive vmlinux.a >>=20 >> Mmm, I don't like this. The expressions that are failing are extremely >> simple, for instance: >>=20 >> Bounded::::from_expr(1) >>=20 >> So if the compiler is unable to assess that this won't fail, this might >> be a deal-breaker for `from_expr` and we might need to remove it. :( >>=20 >> This would also mean a lot more runtime checks when working with >> bitfields and registers. Or can we assume that this is a compiler >> problem on this particular architecture? > > Yeah, it sounds like from_expr() isn't going to work. It would be a pity but we can replace `from_expr` with an unsafe `new_unchecked` for these cases where the caller is absolutely sure of their input. I have tried on bitfield/Nova and the result is not too bad. Still, this is a bummer - it is much better to have the compiler validate safety properties than relying on a SAFETY comment. I notice that loongarch is a Tier 2 Rust platform, but I suppose that's not an excuse to let it not build? ^_^; If I had to bet I'd wager that in this case the "shift left then back right" technique to check the bounds is not working well. I will try to find an alternative, but meanwhile we should probably remove `from_expr`. I will send a patch to that effect unless told otherwise.