[PATCH V11 1/4] rust: Fix "multiple candidates for rmeta dependency core" error

[Mukesh Kumar Chaurasiya]

On Tue, Apr 21, 2026 at 11:38:08AM +0200, Link Mauve wrote:
> Hi Mukesh,
> 
> This patch doesn’t apply on top of mainline, which tree did you base it
> off?
> 
It was on mainline v7.0 tag.
On latest there is a confilict. I'll send out a rebased version.

> On Fri, Apr 17, 2026 at 08:52:50PM +0530, Mukesh Kumar Chaurasiya (IBM) wrote:
> > When building Rust code for powerpc64le with LLVM=1 and -j1, rustc
> > encounters 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 occurs because the build system uses `-L$(objtree)/rust` for host
> > library builds (proc_macro2, quote, syn), which causes rustc to search
> > the rust/ directory. During this search, rustc finds both the kernel's
> > custom libcore.rmeta and gains access to the host's standard library,
> > creating a conflict.
> > 
> > The solution is to separate host libraries into a dedicated rust/host/
> > subdirectory and use `-L$(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
> > 
> > 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 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`.
> > 
> > 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) <mkchauras at gmail.com>
> > ---
> >  rust/Makefile | 38 +++++++++++++++++++++-----------------
> >  1 file changed, 21 insertions(+), 17 deletions(-)
> > 
> > diff --git a/rust/Makefile b/rust/Makefile
> > index 9801af2e1e02..e234b8a39358 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))) \
> 
> The issue is here ↑, --remap-path-prefix=% got removed and the two
> previous lines got merged into one.
> 
Yeah will fix this.
> > -		$(rustc_target_flags) -L$(objtree)/$(obj) \
> > +		$(rustc_target_flags) -L$(objtree)/$(obj)$(if $(rustdoc_host),/host) \
> >  		-Zunstable-options --generate-link-to-definition \
> >  		--output $(rustdoc_output) \
> >  		--crate-name $(subst rustdoc-,,$@) \
> […]
> 
> Thanks anyway for iterating on this series!  I’ve started writing a DRM
> driver based off a previous version. :)
> 
That's cool. Thanks.

Regards,
Mukesh
> -- 
> Link Mauve
>