[{"id":3673506,"web_url":"http://patchwork.ozlabs.org/comment/3673506/","msgid":"","date":"2026-04-04T21:04:08","subject":"Re: [PATCH V9 1/4] rust: Fix \"multiple candidates for rmeta\n dependency core\" error","submitter":{"id":73498,"url":"http://patchwork.ozlabs.org/api/people/73498/","name":"Miguel Ojeda","email":"miguel.ojeda.sandonis@gmail.com"},"content":"On Sat, Apr 4, 2026 at 2:16 PM Mukesh Kumar Chaurasiya (IBM)\n wrote:\n>\n> When building Rust code with LLVM=1 with -j1, rustc was encountering\n> an error:\n> \"multiple candidates for `rmeta` dependency `core` found\", with two\n> candidates:\n> 1. The host's standard library from the rustup toolchain\n> 2. The kernel's custom libcore.rmeta in the rust/ directory\n\nPlease clarify in what conditions this happens, e.g. when building\nnatively in an architecture like powerpc for which the target (...)\n\nOtherwise, it sounds like this is something that would be happening to\nessentially everyone just by building with `-j1`, which is not the\ncase.\n\nAlso, since you may need to reword a bit, please take the chance to\nuse the present tense to describe the current state, and then the\nimperative for what is changed. (The past is usually used for\nsomething that already changed in the past, not for something that\nstill happens before the patch is applied -- I hope that makes sense).\n\n> - Update rustdoc-pin_init to use explicit --extern paths for proc macros\n> as pin-init also needs alloc crate from -L$(objtree)/rust. So the proc\n> macros needs an absolute path\n\nAs Gary mentioned, this list may be too exhaustive, i.e. one needs to\nsee it in the diff anyway. Usually what we do is try to summarize, and\nmost importantly, explain the \"why\".\n\nAlso, it doesn't seem like the list covers every change anyway if that\nwas the intention, e.g. the removal of `--out-dir`.\n\n> -rustdoc-quote: private rustc_target_flags = $(quote-flags)\n> +rustdoc-quote: private rustc_target_flags = $(quote-flags) \\\n> + --extern proc_macro2\n\nHmm... why is this needed? The variable already carries the flag, no?\n\n> - --out-dir $(objtree)/$(obj) -L$(objtree)/$(obj) \\\n\nThis looks like an important removal that is not explained/mentioned elsewhere.\n\nAlso, is there a reason why we cannot keep the `-L` here instead of\nadding it in every proc macro library?\n\n> + --extern pin_init_internal=$(abspath $(objtree)/$(obj)/$(libpin_init_internal_name)) \\\n> + --extern macros=$(abspath $(objtree)/$(obj)/$(libmacros_name)) \\\n> + $(call cfgs-to-flags,$(pin_init-cfgs)) \\\n\nHmm... This special handling isn't great, and the fact that it means\nhardcoding/duplicating `pin_init-flags`.\n\nShould we move the proc macros too?\n\n> - --crate-type proc-macro -L$(objtree)/$(obj) \\\n> + --crate-type proc-macro \\\n> + -L$(objtree)/$(obj)/host \\\n\nSpurious newline added?\n\n> - @$(objtree)/include/generated/rustc_cfg $<\n> + @$(objtree)/include/generated/rustc_cfg \\\n> + $(rustc_target_flags) \\\n> + $<\n\nWhy is the variable moved here?\n\nThanks!\n\nCheers,\nMiguel","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=lRFT2Xi+;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=112.213.38.117; helo=lists.ozlabs.org;\n envelope-from=linuxppc-dev+bounces-19325-incoming=patchwork.ozlabs.org@lists.ozlabs.org;\n receiver=patchwork.ozlabs.org)","lists.ozlabs.org;\n arc=pass smtp.remote-ip=\"2607:f8b0:4864:20::132a\" arc.chain=google.com","lists.ozlabs.org;\n dmarc=pass (p=none dis=none) header.from=gmail.com","lists.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=lRFT2Xi+;\n\tdkim-atps=neutral","lists.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gmail.com\n (client-ip=2607:f8b0:4864:20::132a; 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Sat, 04 Apr 2026\n 14:04:20 -0700 (PDT)","X-Mailing-List":"linuxppc-dev@lists.ozlabs.org","List-Id":"","List-Help":"","List-Owner":"","List-Post":"","List-Archive":",\n ","List-Subscribe":",\n ,\n ","List-Unsubscribe":"","Precedence":"list","MIME-Version":"1.0","References":"<20260404121610.1956528-1-mkchauras@gmail.com>\n <20260404121610.1956528-2-mkchauras@gmail.com>","In-Reply-To":"<20260404121610.1956528-2-mkchauras@gmail.com>","From":"Miguel Ojeda ","Date":"Sat, 4 Apr 2026 23:04:08 +0200","X-Gm-Features":"AQROBzCMgLHa7cowntiZYSKVuRyKGh1fP2Cda-tJiBMZoAlSB8e92ElsqLSq1yE","Message-ID":"\n ","Subject":"Re: [PATCH V9 1/4] rust: Fix \"multiple candidates for rmeta\n dependency core\" error","To":"\"Mukesh Kumar Chaurasiya (IBM)\" ","Cc":"maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com,\n\tchleroy@kernel.org, peterz@infradead.org, jpoimboe@kernel.org,\n\tjbaron@akamai.com, aliceryhl@google.com, rostedt@goodmis.org,\n ardb@kernel.org,\n\tojeda@kernel.org, boqun@kernel.org, gary@garyguo.net,\n\tbjorn3_gh@protonmail.com, lossin@kernel.org, a.hindborg@kernel.org,\n\ttmgross@umich.edu, dakr@kernel.org, nathan@kernel.org,\n\tnick.desaulniers+lkml@gmail.com, morbo@google.com, justinstitt@google.com,\n\tlinuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,\n\trust-for-linux@vger.kernel.org, llvm@lists.linux.dev","Content-Type":"text/plain; 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