From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f172.google.com (mail-pf1-f172.google.com [209.85.210.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6C202374730 for ; Fri, 3 Apr 2026 14:53:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775228014; cv=none; b=DCiNAP5gag4EDoln9PcdSqNRAeq8b0XwD+AKnBvUsvdcyiJ6cSHcVV7KIr67blsOnV6rz+8FA/vLxxclPEB+Nj7luhOk/M/xI9+Bs5qSK7856fBFXS1TKYCcfAKdeWbjmfrYQOQMLLZ+usnnURCmySn/EEVP5FoAS9C0y287iOI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775228014; c=relaxed/simple; bh=s41PsyrgmivcxsEasV3F2vMv28LGN20R8nGi2RgZncQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=LzcTaA2iMpVdqyGwOOKi4dOVufBQ3I24nV+6vAj2/k+P5q9tGjFPrPZ1ukZC8aojJEobY7cUGSYVpT6bPXFqPtu8sikI0L14ArSNFmlZnXI6D8YF27/lb/f0+nlqLcw4Cty9yHkpM6Q8r5LgV7C/Qndw4Wk9cjOiq/A0lDgU8Uc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=p+Y9/fF2; arc=none smtp.client-ip=209.85.210.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="p+Y9/fF2" Received: by mail-pf1-f172.google.com with SMTP id d2e1a72fcca58-82d03827316so600688b3a.0 for ; Fri, 03 Apr 2026 07:53:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1775228013; x=1775832813; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=fUTSB1GcQ+ZgkTavCnlkXCyNO/5I/d2MoyKGgMKrfsE=; b=p+Y9/fF2HU/q9BM6BbAVdapW7m1xvPLhcfdI7s0Jyu8nnc9WTg15KQg0XTz6AcUEwY S4HvDQGIJd61RGDC4tPJJD5X/tJv7jyih9BKewfeDyEmJqa+fFfG7L+DmUyci6Be3E+8 FYO/3303Kb62RAvjy2xhvnSzkTrVUyGb28c30wkM5Gwckl72ux0xVJ1tXLFZh/hhk/BE h7fvxPPbXfGz39inXdyg34pqUIuYpLu5WqJq8l3ExxLamI0Es2U+DH9tl3YByPgc+42s ufK7eab9lViUwX8lXC8zE9fVznZVptu812LD5XH6fu7xffru2oBuc2XdvQz/kP/W5L6w exZw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1775228013; x=1775832813; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=fUTSB1GcQ+ZgkTavCnlkXCyNO/5I/d2MoyKGgMKrfsE=; b=Wu0KHgG2gs49TIVzvdpJ9DE/2pN0M+KySci8AGqIPyZ/9m0Evoi0kiBMdO2jstSUkX XWBCiftW1qgyeqtwEPkggB/8KqSskI5qxDKjxOw0YXfgS3n96jDfAOA9m594T1u6ZY3A ELy9JfeUO6ZShWdqa9PXKBzCKIbKWuZJO0Jtv+bfx3pwsKEgwV8tySXQ1B6g4M1aSdt2 kElwcFrafXTm9m5v+uAsl/LiReeJJNTQMOQTTUzWKHBbvx4BQfIrJckWxYNQ2nGNTxgU oOCiSIWyBifAoQNtSwRcKZUt/86vxyE3uLye0IlgeYNLM6xvWGmFmE0JxkomuoSkCKvB 05bw== X-Forwarded-Encrypted: i=1; AJvYcCV29wyDRJIH4VoAbtt0QaDaZurMUXSQdkC6D1pE3nFxVK26L7Y4DkVt5KxFlvLcN+k6JbaVNNTb1VD6uQjvrw==@vger.kernel.org X-Gm-Message-State: AOJu0YyMKgX5L409Bcah/jVE9eSbbaKi+1Mztu8rTZZ+LyH66j5a/nga UU795dcf1MfWKU3BsS3dBAwaat3N5wP3t6S8kXTC6kxhFeQE93+RDm/K X-Gm-Gg: AeBDiesumcrkjmbI6Xdb/cOYaHLnBTIerZ0mG72ZHd8iJHtQqyVR5B0rgKjALIsSmOF NBmCEkdzYU3vYCo08hV9k1+uHnu5eeRjPKgrtpGbEYY8lC80zEX8IgfsrZRw6sizLNydnCMpjwa PHv+H1ArGNTdQ/dxEFE/xc1u8bVMf/FHKa+tUfwxogkLiWYmTmBgR/VF8Ws3g94bHTV+slkviUO RMaYOKz1pvhDiHv470ETTnjrj/ySD3WDLiVcPbMJ00cuimXXiBxBzzqZZaqp8EgsXGWmVms+Job eZv71uBdBpQt86G3D6UmFkCMnZZWNO80hUgpwDPX64fqtjkGlMFZzWyVb24ZTZlMDHW7FS2c1rS Irm88XOcyeESBzXlKcofSpCLTaBag+MgYzC4RVm+ccwqlerTpC2pbbYXZ3Z4y5DFXU7Jr+w3dPO BqElMt+fdYmxcTY8jub+gr5uTy9ECVG4jejT9RLih4JQILvfnxb7yj0AL1qB9yniTRUIAiF9/L3 qQ7ehUR5lkKrg== X-Received: by 2002:a05:6a00:3699:b0:81f:544b:3998 with SMTP id d2e1a72fcca58-82d0dd20f4amr2711320b3a.26.1775228012689; Fri, 03 Apr 2026 07:53:32 -0700 (PDT) Received: from li-1a3e774c-28e4-11b2-a85c-acc9f2883e29.ibm.com.com ([106.51.160.44]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82cf9ca4efesm6301682b3a.61.2026.04.03.07.53.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Apr 2026 07:53:32 -0700 (PDT) From: "Mukesh Kumar Chaurasiya (IBM)" To: 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, 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, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, llvm@lists.linux.dev Cc: "Mukesh Kumar Chaurasiya (IBM)" Subject: [PATCH V8 1/4] rust: Fix "multiple candidates for rmeta dependency core" error Date: Fri, 3 Apr 2026 20:23:05 +0530 Message-ID: <20260403145308.1042622-2-mkchauras@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260403145308.1042622-1-mkchauras@gmail.com> References: <20260403145308.1042622-1-mkchauras@gmail.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When building Rust code with LLVM=1 with -j1, rustc was encountering an error: "multiple candidates for `rmeta` dependency `core` found", with two candidates: 1. The host's standard library from the rustup toolchain 2. The kernel's custom libcore.rmeta in the rust/ directory This occurred because the build system was using `-L$(objtree)/rust` for host library builds (proc_macro2, quote, syn), which caused rustc to search the rust/ directory. During this search, rustc would find both the kernel's custom libcore.rmeta and gain access to the host's standard library, creating a conflict. The solution is to separate host libraries into a dedicated rust/host/ subdirectory and use `-L$(objtree)/rust/host` for host builds instead of `-L$(objtree)/rust`. This ensures that: 1. Host library builds (proc_macro2, quote, syn) only search rust/host/ and never encounter the kernel's libcore.rmeta 2. Proc macro builds use `-L$(objtree)/rust/host` to find their dependencies 3. Test builds use `-L$(objtree)/rust/test` for their dependencies 4. Target builds continue to use `-L$(objtree)/rust` as before Special handling is added for rustdoc-pin_init, which is a host build (to access the alloc crate) but depends on proc macros from the main rust/ directory. It uses explicit `--extern` paths with absolute paths to reference the proc macros without adding `-L$(objtree)/rust`, which would reintroduce the conflict. The rust/host/ directory is added to clean-files to ensure it's removed during `make clean`. Changes: - Add clean-files := host/ to clean the generated directory - Change host library targets from lib*.rlib to host/lib*.rlib - Update cmd_rustc_procmacrolibrary to create host/ directory - Update cmd_rustc_procmacro to use -L$(objtree)/rust/host - Update cmd_rustdoc to use -L$(objtree)/rust/host for host builds - Update cmd_rustc_test_library to use -L$(objtree)/rust/test - Update rustdoc-pin_init to use explicit --extern paths for proc macros Link: https://github.com/Rust-for-Linux/linux/issues/105 Link: https://github.com/linuxppc/issues/issues/451 Signed-off-by: Mukesh Kumar Chaurasiya (IBM) --- rust/Makefile | 63 ++++++++++++++++++++++++++++++++------------------- 1 file changed, 40 insertions(+), 23 deletions(-) diff --git a/rust/Makefile b/rust/Makefile index 9801af2e1e02..762bddc868e4 100644 --- a/rust/Makefile +++ b/rust/Makefile @@ -3,6 +3,9 @@ # Where to place rustdoc generated documentation rustdoc_output := $(objtree)/Documentation/output/rust/rustdoc +# Clean generated host directory +clean-files := host/ + obj-$(CONFIG_RUST) += core.o compiler_builtins.o ffi.o always-$(CONFIG_RUST) += exports_core_generated.h @@ -27,7 +30,7 @@ endif obj-$(CONFIG_RUST) += exports.o -always-$(CONFIG_RUST) += libproc_macro2.rlib libquote.rlib libsyn.rlib +always-$(CONFIG_RUST) += host/libproc_macro2.rlib host/libquote.rlib host/libsyn.rlib always-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated.rs always-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated_kunit.c @@ -150,7 +153,7 @@ quiet_cmd_rustdoc = RUSTDOC $(if $(rustdoc_host),H, ) $< OBJTREE=$(abspath $(objtree)) \ $(RUSTDOC) $(filter-out $(skip_flags) --remap-path-prefix=% --remap-path-scope=%, \ $(if $(rustdoc_host),$(rust_common_flags),$(rust_flags))) \ - $(rustc_target_flags) -L$(objtree)/$(obj) \ + $(rustc_target_flags) -L$(objtree)/$(obj)$(if $(rustdoc_host),/host) \ -Zunstable-options --generate-link-to-definition \ --output $(rustdoc_output) \ --crate-name $(subst rustdoc-,,$@) \ @@ -193,13 +196,16 @@ rustdoc-proc_macro2: $(src)/proc-macro2/lib.rs rustdoc-clean FORCE +$(call if_changed,rustdoc) rustdoc-quote: private rustdoc_host = yes -rustdoc-quote: private rustc_target_flags = $(quote-flags) +rustdoc-quote: private rustc_target_flags = $(quote-flags) \ + --extern proc_macro2=$(abspath $(objtree)/$(obj)/host/libproc_macro2.rlib) rustdoc-quote: private skip_flags = $(quote-skip_flags) rustdoc-quote: $(src)/quote/lib.rs rustdoc-clean rustdoc-proc_macro2 FORCE +$(call if_changed,rustdoc) rustdoc-syn: private rustdoc_host = yes -rustdoc-syn: private rustc_target_flags = $(syn-flags) +rustdoc-syn: private rustc_target_flags = $(syn-flags) \ + --extern proc_macro2=$(abspath $(objtree)/$(obj)/host/libproc_macro2.rlib) \ + --extern quote=$(abspath $(objtree)/$(obj)/host/libquote.rlib) rustdoc-syn: $(src)/syn/lib.rs rustdoc-clean rustdoc-quote FORCE +$(call if_changed,rustdoc) @@ -236,7 +242,10 @@ rustdoc-pin_init_internal: $(src)/pin-init/internal/src/lib.rs \ +$(call if_changed,rustdoc) rustdoc-pin_init: private rustdoc_host = yes -rustdoc-pin_init: private rustc_target_flags = $(pin_init-flags) \ +rustdoc-pin_init: private rustc_target_flags = \ + --extern pin_init_internal=$(abspath $(objtree)/$(obj)/$(libpin_init_internal_name)) \ + --extern macros=$(abspath $(objtree)/$(obj)/$(libmacros_name)) \ + $(call cfgs-to-flags,$(pin_init-cfgs)) \ --extern alloc --cfg feature=\"alloc\" rustdoc-pin_init: $(src)/pin-init/src/lib.rs rustdoc-pin_init_internal \ rustdoc-macros FORCE @@ -369,7 +378,9 @@ rusttest: rusttest-macros rusttest-macros: private rustc_target_flags = --extern proc_macro \ --extern macros --extern kernel --extern pin_init \ - --extern proc_macro2 --extern quote --extern syn + --extern proc_macro2=$(abspath $(objtree)/$(obj)/test/libproc_macro2.rlib) \ + --extern quote=$(abspath $(objtree)/$(obj)/test/libquote.rlib) \ + --extern syn=$(abspath $(objtree)/$(obj)/test/libsyn.rlib) rusttest-macros: private rustdoc_test_target_flags = --crate-type proc-macro rusttest-macros: $(src)/macros/lib.rs \ rusttestlib-macros rusttestlib-kernel rusttestlib-pin_init FORCE @@ -525,48 +536,54 @@ $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FORCE quiet_cmd_rustc_procmacrolibrary = $(RUSTC_OR_CLIPPY_QUIET) PL $@ cmd_rustc_procmacrolibrary = \ + mkdir -p $(dir $@); \ $(if $(skip_clippy),$(RUSTC),$(RUSTC_OR_CLIPPY)) \ $(filter-out $(skip_flags),$(rust_common_flags) $(rustc_target_flags)) \ --emit=dep-info=$(depfile) --emit=link=$@ --crate-type rlib -O \ - --out-dir $(objtree)/$(obj) -L$(objtree)/$(obj) \ --crate-name $(patsubst lib%.rlib,%,$(notdir $@)) $< -$(obj)/libproc_macro2.rlib: private skip_clippy = 1 -$(obj)/libproc_macro2.rlib: private rustc_target_flags = $(proc_macro2-flags) -$(obj)/libproc_macro2.rlib: $(src)/proc-macro2/lib.rs FORCE +$(obj)/host/libproc_macro2.rlib: private skip_clippy = 1 +$(obj)/host/libproc_macro2.rlib: private rustc_target_flags = $(proc_macro2-flags) +$(obj)/host/libproc_macro2.rlib: $(src)/proc-macro2/lib.rs FORCE +$(call if_changed_dep,rustc_procmacrolibrary) -$(obj)/libquote.rlib: private skip_clippy = 1 -$(obj)/libquote.rlib: private skip_flags = $(quote-skip_flags) -$(obj)/libquote.rlib: private rustc_target_flags = $(quote-flags) -$(obj)/libquote.rlib: $(src)/quote/lib.rs $(obj)/libproc_macro2.rlib FORCE +$(obj)/host/libquote.rlib: private skip_clippy = 1 +$(obj)/host/libquote.rlib: private skip_flags = $(quote-skip_flags) +$(obj)/host/libquote.rlib: private rustc_target_flags = $(quote-flags) \ + --extern proc_macro2=$(abspath $(objtree)/$(obj)/host/libproc_macro2.rlib) +$(obj)/host/libquote.rlib: $(src)/quote/lib.rs $(obj)/host/libproc_macro2.rlib FORCE +$(call if_changed_dep,rustc_procmacrolibrary) -$(obj)/libsyn.rlib: private skip_clippy = 1 -$(obj)/libsyn.rlib: private rustc_target_flags = $(syn-flags) -$(obj)/libsyn.rlib: $(src)/syn/lib.rs $(obj)/libquote.rlib FORCE +$(obj)/host/libsyn.rlib: private skip_clippy = 1 +$(obj)/host/libsyn.rlib: private rustc_target_flags = $(syn-flags) \ + --extern proc_macro2=$(abspath $(objtree)/$(obj)/host/libproc_macro2.rlib) \ + --extern quote=$(abspath $(objtree)/$(obj)/host/libquote.rlib) +$(obj)/host/libsyn.rlib: $(src)/syn/lib.rs $(obj)/host/libquote.rlib FORCE +$(call if_changed_dep,rustc_procmacrolibrary) quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@ cmd_rustc_procmacro = \ - $(RUSTC_OR_CLIPPY) $(rust_common_flags) $(rustc_target_flags) \ + $(RUSTC_OR_CLIPPY) $(rust_common_flags) \ -Clinker-flavor=gcc -Clinker=$(HOSTCC) \ -Clink-args='$(call escsq,$(KBUILD_PROCMACROLDFLAGS))' \ --emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \ - --crate-type proc-macro -L$(objtree)/$(obj) \ + --crate-type proc-macro \ + -L$(objtree)/$(obj)/host \ --crate-name $(patsubst lib%.$(libmacros_extension),%,$(notdir $@)) \ - @$(objtree)/include/generated/rustc_cfg $< + @$(objtree)/include/generated/rustc_cfg \ + $(rustc_target_flags) \ + $< # Procedural macros can only be used with the `rustc` that compiled it. $(obj)/$(libmacros_name): private rustc_target_flags = \ --extern proc_macro2 --extern quote --extern syn -$(obj)/$(libmacros_name): $(src)/macros/lib.rs $(obj)/libproc_macro2.rlib \ - $(obj)/libquote.rlib $(obj)/libsyn.rlib FORCE +$(obj)/$(libmacros_name): $(src)/macros/lib.rs $(obj)/host/libproc_macro2.rlib \ + $(obj)/host/libquote.rlib $(obj)/host/libsyn.rlib FORCE +$(call if_changed_dep,rustc_procmacro) $(obj)/$(libpin_init_internal_name): private rustc_target_flags = $(pin_init_internal-flags) $(obj)/$(libpin_init_internal_name): $(src)/pin-init/internal/src/lib.rs \ - $(obj)/libproc_macro2.rlib $(obj)/libquote.rlib $(obj)/libsyn.rlib FORCE + $(obj)/host/libproc_macro2.rlib $(obj)/host/libquote.rlib $(obj)/host/libsyn.rlib FORCE +$(call if_changed_dep,rustc_procmacro) # `rustc` requires `-Zunstable-options` to use custom target specifications -- 2.53.0