Re: [PATCH v2 3/3] build: rust: provide an option to inline C helpers into Rust

[Alice Ryhl]

On Fri, Mar 13, 2026 at 05:40:12PM -0700, Nathan Chancellor wrote:
> On Fri, Mar 06, 2026 at 05:32:33PM +0000, Alice Ryhl wrote:
> > On Tue, Feb 03, 2026 at 11:34:10AM +0000, Alice Ryhl wrote:
> > >  $(obj)/bindings/bindings_helpers_generated.rs: $(src)/helpers/helpers.c FORCE
> > >  	$(call if_changed_dep,bindgen)
> > >  
> > > +quiet_cmd_rust_helper = HELPER  $@
> > > +      cmd_rust_helper = \
> > > +	$(CC) $(filter-out $(CFLAGS_REMOVE_helpers/helpers.o), $(c_flags)) \
> > > +		-c -g0 $< $(if $(filter %_module.bc,$@),-DMODULE) -emit-llvm -o $@
> > > +
> > > +$(obj)/helpers/helpers.bc $(obj)/helpers/helpers_module.bc: $(src)/helpers/helpers.c FORCE
> > > +	+$(call if_changed_dep,rust_helper)
> > 
> > I think this needs:
> > 
> > $(obj)/helpers/helpers.bc: private part-of-builtin := y
> > $(obj)/helpers/helpers_module.bc: private part-of-module := y
> > 
> > at least it seems to make a difference for AutoFDO.
> 
> Would
> 
>   $(obj)/helpers/helpers.bc $(obj)/helpers/helpers_module.bc: private is-kernel-object := y
> 
> work as well? Presumably, this is because c_flags only has the AutoFDO
> flags when is-kernel-object is set, which is only true when
> helpers/helpers.o is a part of obj-y.

I assume so, but isn't it more correct to set part-of-builtin and
part-of-module? I don't see any make rules making use of those directly
(instead of is-kernel-object) right now, but if someone adds such uses,
then this could become wrong, right?

Alice