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The `uapi` crate has the same pro= blem >> >> > but nothing from it is exported. >> >> > >> >> > In practice this goes unnoticed because the only functions in `uapi= ` >> >> > are the trivial `Default` implementations generated by `bindgen`, >> >> > which rustc inlines across crates. With CONFIG_RUST_DEBUG_ASSERTION= S=3Dy >> >> > however, the `Default` implementation for structs can grow past the >> >> > automatic cross-crate inlining threshold. The module then reference= s the >> >> > copy in `uapi.o`, which is not exported, and the build fails: >> >> > >> >> > ERROR: modpost: drivers/gpu/nova-drm.ko: symbol '_RNvXsH_Csk9v2ZI= pWbWt_4uapiNtB5_17drm_nova_info_gpuNtNtCsfr3MPOfBGpN_4core7default7Default7= default' undefined! >> >>=20 >> >> Hmm, uapi' ideally should just be type exports and produce no code. >> >>=20 >> >> Default implementation should carry `#[inline]` annotation so they're >> >> only codegenned in actual user crate. Rust's `#[derive(Default)]` wou= ld always >> >> add that. Can you check if that's bindgen-produced manual Default imp= l that >> >> somehow misses the attribute? >> > >> > Right, bindgen-produced Default impl do not have that attribute. For e= xample >> > here is the bindgen generated implementation I see: >>=20 >> Perhaps you can open an issue upstream?=20 > > For sure - see https://github.com/rust-lang/rust-bindgen/issues/3494 > > I wasn't quite sure of the justification for why we don't want to just ex= port > these, so please feel free to comment there. Hi Alistair, The justification is that the uapi crate should have no cost on its own (so= it should generate no code), because that's just an API. Whoever uses it shoul= d pay the cost. Exporting the symbols would hide all that. So, I'd even suggest that ideally we don't link the object at all, so it be= haves uniformly, built-in modules or not. Best, Gary > >> > >> > impl Default for drm_nova_info_gpu { >> > fn default() -> Self { >> > let mut s =3D ::core::mem::MaybeUninit::::uninit(); >> > unsafe { >> > ::core::ptr::write_bytes(s.as_mut_ptr(), 0, 1); >> > s.assume_init() >> > } >> > } >> > } >> > >> > Manually adding #[inline] fixes the problem of course. I guess we coul= d add some >> > sed Makefile hackery to manually add it. For example something like th= e below, >> > not sure if that would be preferred? >>=20 >> Yeah, textual hacks are a bit too fragile (especially that it'll break w= hen >> upstream bindgen adds these annotations). So if you need these impls, I = think >> exporting these symbols are fine. > > Fun though :) But yes, I agree this is pretty hacky so would rather expor= t the > symbols, at least until bindgen is fixed. > >> That said, you can achieve what you need with `drm_nova_info_gpu::zeroed= ()` >> instead? > > We could, but I'd rather fix this here as people are inevitably going to = try and > use default::Default() and the linker errors that come from it are pretty= obtuse > and difficult to diagnose what the problem really is. > > - Alistair > >> Best, >> Gary >>=20 >> > >> > --- >> > >> > diff --cc rust/Makefile >> > index da1a7409d984,da1a7409d984..535a3bf181bb >> > --- a/rust/Makefile >> > +++ b/rust/Makefile >> > @@@ -525,13 -525,13 +525,16 @@@ quiet_cmd_bindgen =3D BINDGEN $ >> > $(obj)/bindings/bindings_generated.rs: private bindgen_target_flags = =3D \ >> > $(shell grep -Ev '^#|^$$' $(src)/bindgen_parameters) >> > $(obj)/bindings/bindings_generated.rs: private bindgen_target_extra = =3D ; \ >> > -- sed -Ei 's/pub const RUST_CONST_HELPER_([a-zA-Z0-9_]*)/pub const= \1/g' $@ >> > ++ sed -Ei 's/pub const RUST_CONST_HELPER_([a-zA-Z0-9_]*)/pub const= \1/g; \ >> > ++ s/^([[:space:]]*)fn default\(\) -> Self \{/\1#[inline]\n\1fn= default() -> Self {/' $@ >> > $(obj)/bindings/bindings_generated.rs: $(src)/bindings/bindings_help= er.h \ >> > $(src)/bindgen_parameters FORCE >> > $(call if_changed_dep,bindgen) >> > =20 >> > $(obj)/uapi/uapi_generated.rs: private bindgen_target_flags =3D \ >> > $(shell grep -Ev '^#|^$$' $(src)/bindgen_parameters) >> > ++$(obj)/uapi/uapi_generated.rs: private bindgen_target_extra =3D ; \ >> > ++ sed -Ei 's/^([[:space:]]*)fn default\(\) -> Self \{/\1#[inline]\= n\1fn default() -> Self {/' $@ >> > $(obj)/uapi/uapi_generated.rs: $(src)/uapi/uapi_helper.h \ >> > $(src)/bindgen_parameters FORCE >> > $(call if_changed_dep,bindgen) >> > >>=20