[PATCH] rust: kbuild: export symbols from the `uapi` crate

[PATCH] rust: kbuild: export symbols from the `uapi` crate

[Alistair Popple]

Symbols from the `bindings` crate and the C helpers are exported so
that loadable modules can link against code the compiler chose not to
instantiate in the module itself. The `uapi` crate has the same problem
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_ASSERTIONS=y
however, the `Default` implementation for structs can grow past the
automatic cross-crate inlining threshold. The module then references the
copy in `uapi.o`, which is not exported, and the build fails:

  ERROR: modpost: drivers/gpu/nova-drm.ko: symbol '_RNvXsH_Csk9v2ZIpWbWt_4uapiNtB5_17drm_nova_info_gpuNtNtCsfr3MPOfBGpN_4core7default7Default7default' undefined!

Fix this by exporting the `uapi` symbols in the same way as `bindings`.

Fixes: 4e1746656839 ("rust: uapi: Add UAPI crate")
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Assisted-by: LLM
---
 rust/Makefile  | 7 ++++++-
 rust/exports.c | 1 +
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/rust/Makefile b/rust/Makefile
index da1a7409d984..083992a5c1c9 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -27,6 +27,7 @@ always-$(CONFIG_RUST) += exports_bindings_generated.h exports_kernel_generated.h
 
 always-$(CONFIG_RUST) += uapi/uapi_generated.rs
 obj-$(CONFIG_RUST) += uapi.o
+always-$(CONFIG_RUST) += exports_uapi_generated.h
 
 ifdef CONFIG_RUST_BUILD_ASSERT_ALLOW
 obj-$(CONFIG_RUST) += build_error.o
@@ -575,7 +576,8 @@ $(obj)/exports_core_generated.h: $(obj)/core.o FORCE
 # in the crate where they are defined. Other helpers, called from non-inline
 # functions, may not be exported, in principle. However, in general, the Rust
 # compiler does not guarantee codegen will be performed for a non-inline
-# function either. Therefore, we export all symbols from helpers and bindings.
+# function either. Therefore, we export all symbols from helpers, bindings and
+# uapi.
 # In the future, this may be revisited to reduce the number of exports after
 # the compiler is informed about the places codegen is required.
 $(obj)/exports_helpers_generated.h: $(obj)/helpers/helpers.o FORCE
@@ -587,6 +589,9 @@ $(obj)/exports_bindings_generated.h: $(obj)/bindings.o FORCE
 $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FORCE
 	$(call if_changed,exports)
 
+$(obj)/exports_uapi_generated.h: $(obj)/uapi.o FORCE
+	$(call if_changed,exports)
+
 quiet_cmd_rustc_procmacrolibrary = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) PL $@
       cmd_rustc_procmacrolibrary = \
 	$(rustc_target_envs) \
diff --git a/rust/exports.c b/rust/exports.c
index 1b52460b0f4e..434f0b73151f 100644
--- a/rust/exports.c
+++ b/rust/exports.c
@@ -17,6 +17,7 @@
 
 #include "exports_core_generated.h"
 #include "exports_bindings_generated.h"
+#include "exports_uapi_generated.h"
 #include "exports_kernel_generated.h"
 
 #ifndef CONFIG_RUST_INLINE_HELPERS

base-commit: b705c185105762676aa6ec16cf976101df87cc35
-- 
2.54.0

Re: [PATCH] rust: kbuild: export symbols from the `uapi` crate

[Gary Guo]

On Wed Sep 9, 2026 at 7:06 AM BST, Alistair Popple wrote:
> Symbols from the `bindings` crate and the C helpers are exported so
> that loadable modules can link against code the compiler chose not to
> instantiate in the module itself. The `uapi` crate has the same problem
> 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_ASSERTIONS=y
> however, the `Default` implementation for structs can grow past the
> automatic cross-crate inlining threshold. The module then references the
> copy in `uapi.o`, which is not exported, and the build fails:
>
>   ERROR: modpost: drivers/gpu/nova-drm.ko: symbol '_RNvXsH_Csk9v2ZIpWbWt_4uapiNtB5_17drm_nova_info_gpuNtNtCsfr3MPOfBGpN_4core7default7Default7default' undefined!

Hmm, uapi' ideally should just be type exports and produce no code.

Default implementation should carry `#[inline]` annotation so they're
only codegenned in actual user crate. Rust's `#[derive(Default)]` would always
add that. Can you check if that's bindgen-produced manual Default impl that
somehow misses the attribute?

Best,
Gary

>
> Fix this by exporting the `uapi` symbols in the same way as `bindings`.
>
> Fixes: 4e1746656839 ("rust: uapi: Add UAPI crate")
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> Assisted-by: LLM
> ---
>  rust/Makefile  | 7 ++++++-
>  rust/exports.c | 1 +
>  2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/rust/Makefile b/rust/Makefile
> index da1a7409d984..083992a5c1c9 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -27,6 +27,7 @@ always-$(CONFIG_RUST) += exports_bindings_generated.h exports_kernel_generated.h
>  
>  always-$(CONFIG_RUST) += uapi/uapi_generated.rs
>  obj-$(CONFIG_RUST) += uapi.o
> +always-$(CONFIG_RUST) += exports_uapi_generated.h
>  
>  ifdef CONFIG_RUST_BUILD_ASSERT_ALLOW
>  obj-$(CONFIG_RUST) += build_error.o
> @@ -575,7 +576,8 @@ $(obj)/exports_core_generated.h: $(obj)/core.o FORCE
>  # in the crate where they are defined. Other helpers, called from non-inline
>  # functions, may not be exported, in principle. However, in general, the Rust
>  # compiler does not guarantee codegen will be performed for a non-inline
> -# function either. Therefore, we export all symbols from helpers and bindings.
> +# function either. Therefore, we export all symbols from helpers, bindings and
> +# uapi.
>  # In the future, this may be revisited to reduce the number of exports after
>  # the compiler is informed about the places codegen is required.
>  $(obj)/exports_helpers_generated.h: $(obj)/helpers/helpers.o FORCE
> @@ -587,6 +589,9 @@ $(obj)/exports_bindings_generated.h: $(obj)/bindings.o FORCE
>  $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FORCE
>  	$(call if_changed,exports)
>  
> +$(obj)/exports_uapi_generated.h: $(obj)/uapi.o FORCE
> +	$(call if_changed,exports)
> +
>  quiet_cmd_rustc_procmacrolibrary = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) PL $@
>        cmd_rustc_procmacrolibrary = \
>  	$(rustc_target_envs) \
> diff --git a/rust/exports.c b/rust/exports.c
> index 1b52460b0f4e..434f0b73151f 100644
> --- a/rust/exports.c
> +++ b/rust/exports.c
> @@ -17,6 +17,7 @@
>  
>  #include "exports_core_generated.h"
>  #include "exports_bindings_generated.h"
> +#include "exports_uapi_generated.h"
>  #include "exports_kernel_generated.h"
>  
>  #ifndef CONFIG_RUST_INLINE_HELPERS
>
> base-commit: b705c185105762676aa6ec16cf976101df87cc35

Re: [PATCH] rust: kbuild: export symbols from the `uapi` crate

[Alistair Popple]

On 2026-09-10 at 00:25 +1000, Gary Guo <gary@garyguo.net> wrote...
> On Wed Sep 9, 2026 at 7:06 AM BST, Alistair Popple wrote:
> > Symbols from the `bindings` crate and the C helpers are exported so
> > that loadable modules can link against code the compiler chose not to
> > instantiate in the module itself. The `uapi` crate has the same problem
> > 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_ASSERTIONS=y
> > however, the `Default` implementation for structs can grow past the
> > automatic cross-crate inlining threshold. The module then references the
> > copy in `uapi.o`, which is not exported, and the build fails:
> >
> >   ERROR: modpost: drivers/gpu/nova-drm.ko: symbol '_RNvXsH_Csk9v2ZIpWbWt_4uapiNtB5_17drm_nova_info_gpuNtNtCsfr3MPOfBGpN_4core7default7Default7default' undefined!
> 
> Hmm, uapi' ideally should just be type exports and produce no code.
> 
> Default implementation should carry `#[inline]` annotation so they're
> only codegenned in actual user crate. Rust's `#[derive(Default)]` would always
> add that. Can you check if that's bindgen-produced manual Default impl that
> somehow misses the attribute?

Right, bindgen-produced Default impl do not have that attribute. For example
here is the bindgen generated implementation I see:

impl Default for drm_nova_info_gpu {
    fn default() -> Self {
        let mut s = ::core::mem::MaybeUninit::<Self>::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 could add some
sed Makefile hackery to manually add it. For example something like the below,
not sure if that would be preferred?

---

diff --cc rust/Makefile
index da1a7409d984,da1a7409d984..535a3bf181bb
--- a/rust/Makefile
+++ b/rust/Makefile
@@@ -525,13 -525,13 +525,16 @@@ quiet_cmd_bindgen = BINDGEN $
  $(obj)/bindings/bindings_generated.rs: private bindgen_target_flags = \
      $(shell grep -Ev '^#|^$$' $(src)/bindgen_parameters)
  $(obj)/bindings/bindings_generated.rs: private bindgen_target_extra = ; \
--    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_helper.h \
      $(src)/bindgen_parameters FORCE
        $(call if_changed_dep,bindgen)
  
  $(obj)/uapi/uapi_generated.rs: private bindgen_target_flags = \
      $(shell grep -Ev '^#|^$$' $(src)/bindgen_parameters)
++$(obj)/uapi/uapi_generated.rs: private bindgen_target_extra = ; \
++    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)


> Best,
> Gary
> 
> >
> > Fix this by exporting the `uapi` symbols in the same way as `bindings`.
> >
> > Fixes: 4e1746656839 ("rust: uapi: Add UAPI crate")
> > Signed-off-by: Alistair Popple <apopple@nvidia.com>
> > Assisted-by: LLM
> > ---
> >  rust/Makefile  | 7 ++++++-
> >  rust/exports.c | 1 +
> >  2 files changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/rust/Makefile b/rust/Makefile
> > index da1a7409d984..083992a5c1c9 100644
> > --- a/rust/Makefile
> > +++ b/rust/Makefile
> > @@ -27,6 +27,7 @@ always-$(CONFIG_RUST) += exports_bindings_generated.h exports_kernel_generated.h
> >  
> >  always-$(CONFIG_RUST) += uapi/uapi_generated.rs
> >  obj-$(CONFIG_RUST) += uapi.o
> > +always-$(CONFIG_RUST) += exports_uapi_generated.h
> >  
> >  ifdef CONFIG_RUST_BUILD_ASSERT_ALLOW
> >  obj-$(CONFIG_RUST) += build_error.o
> > @@ -575,7 +576,8 @@ $(obj)/exports_core_generated.h: $(obj)/core.o FORCE
> >  # in the crate where they are defined. Other helpers, called from non-inline
> >  # functions, may not be exported, in principle. However, in general, the Rust
> >  # compiler does not guarantee codegen will be performed for a non-inline
> > -# function either. Therefore, we export all symbols from helpers and bindings.
> > +# function either. Therefore, we export all symbols from helpers, bindings and
> > +# uapi.
> >  # In the future, this may be revisited to reduce the number of exports after
> >  # the compiler is informed about the places codegen is required.
> >  $(obj)/exports_helpers_generated.h: $(obj)/helpers/helpers.o FORCE
> > @@ -587,6 +589,9 @@ $(obj)/exports_bindings_generated.h: $(obj)/bindings.o FORCE
> >  $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FORCE
> >  	$(call if_changed,exports)
> >  
> > +$(obj)/exports_uapi_generated.h: $(obj)/uapi.o FORCE
> > +	$(call if_changed,exports)
> > +
> >  quiet_cmd_rustc_procmacrolibrary = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) PL $@
> >        cmd_rustc_procmacrolibrary = \
> >  	$(rustc_target_envs) \
> > diff --git a/rust/exports.c b/rust/exports.c
> > index 1b52460b0f4e..434f0b73151f 100644
> > --- a/rust/exports.c
> > +++ b/rust/exports.c
> > @@ -17,6 +17,7 @@
> >  
> >  #include "exports_core_generated.h"
> >  #include "exports_bindings_generated.h"
> > +#include "exports_uapi_generated.h"
> >  #include "exports_kernel_generated.h"
> >  
> >  #ifndef CONFIG_RUST_INLINE_HELPERS
> >
> > base-commit: b705c185105762676aa6ec16cf976101df87cc35
> 
> 

Re: [PATCH] rust: kbuild: export symbols from the `uapi` crate

[Alice Ryhl]

On Thu, Sep 10, 2026 at 4:22 AM Alistair Popple <apopple@nvidia.com> wrote:
>
> On 2026-09-10 at 00:25 +1000, Gary Guo <gary@garyguo.net> wrote...
> > On Wed Sep 9, 2026 at 7:06 AM BST, Alistair Popple wrote:
> > > Symbols from the `bindings` crate and the C helpers are exported so
> > > that loadable modules can link against code the compiler chose not to
> > > instantiate in the module itself. The `uapi` crate has the same problem
> > > 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_ASSERTIONS=y
> > > however, the `Default` implementation for structs can grow past the
> > > automatic cross-crate inlining threshold. The module then references the
> > > copy in `uapi.o`, which is not exported, and the build fails:
> > >
> > >   ERROR: modpost: drivers/gpu/nova-drm.ko: symbol '_RNvXsH_Csk9v2ZIpWbWt_4uapiNtB5_17drm_nova_info_gpuNtNtCsfr3MPOfBGpN_4core7default7Default7default' undefined!
> >
> > Hmm, uapi' ideally should just be type exports and produce no code.
> >
> > Default implementation should carry `#[inline]` annotation so they're
> > only codegenned in actual user crate. Rust's `#[derive(Default)]` would always
> > add that. Can you check if that's bindgen-produced manual Default impl that
> > somehow misses the attribute?
>
> Right, bindgen-produced Default impl do not have that attribute. For example
> here is the bindgen generated implementation I see:
>
> impl Default for drm_nova_info_gpu {
>     fn default() -> Self {
>         let mut s = ::core::mem::MaybeUninit::<Self>::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 could add some
> sed Makefile hackery to manually add it. For example something like the below,
> not sure if that would be preferred?

I think we should just export those symbols so it works on older
bindgen, and then try to fix bindgen to emit #[inline] so that people
with a new bindgen version do not get the symbols.

Alice

Re: [PATCH] rust: kbuild: export symbols from the `uapi` crate

[Gary Guo]

On Thu Sep 10, 2026 at 3:21 AM BST, Alistair Popple wrote:
> On 2026-09-10 at 00:25 +1000, Gary Guo <gary@garyguo.net> wrote...
>> On Wed Sep 9, 2026 at 7:06 AM BST, Alistair Popple wrote:
>> > Symbols from the `bindings` crate and the C helpers are exported so
>> > that loadable modules can link against code the compiler chose not to
>> > instantiate in the module itself. The `uapi` crate has the same problem
>> > 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_ASSERTIONS=y
>> > however, the `Default` implementation for structs can grow past the
>> > automatic cross-crate inlining threshold. The module then references the
>> > copy in `uapi.o`, which is not exported, and the build fails:
>> >
>> >   ERROR: modpost: drivers/gpu/nova-drm.ko: symbol '_RNvXsH_Csk9v2ZIpWbWt_4uapiNtB5_17drm_nova_info_gpuNtNtCsfr3MPOfBGpN_4core7default7Default7default' undefined!
>> 
>> Hmm, uapi' ideally should just be type exports and produce no code.
>> 
>> Default implementation should carry `#[inline]` annotation so they're
>> only codegenned in actual user crate. Rust's `#[derive(Default)]` would always
>> add that. Can you check if that's bindgen-produced manual Default impl that
>> somehow misses the attribute?
>
> Right, bindgen-produced Default impl do not have that attribute. For example
> here is the bindgen generated implementation I see:

Perhaps you can open an issue upstream? 

>
> impl Default for drm_nova_info_gpu {
>     fn default() -> Self {
>         let mut s = ::core::mem::MaybeUninit::<Self>::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 could add some
> sed Makefile hackery to manually add it. For example something like the below,
> not sure if that would be preferred?

Yeah, textual hacks are a bit too fragile (especially that it'll break when
upstream bindgen adds these annotations). So if you need these impls, I think
exporting these symbols are fine.

That said, you can achieve what you need with `drm_nova_info_gpu::zeroed()`
instead?

Best,
Gary

>
> ---
>
> diff --cc rust/Makefile
> index da1a7409d984,da1a7409d984..535a3bf181bb
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@@ -525,13 -525,13 +525,16 @@@ quiet_cmd_bindgen = BINDGEN $
>   $(obj)/bindings/bindings_generated.rs: private bindgen_target_flags = \
>       $(shell grep -Ev '^#|^$$' $(src)/bindgen_parameters)
>   $(obj)/bindings/bindings_generated.rs: private bindgen_target_extra = ; \
> --    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_helper.h \
>       $(src)/bindgen_parameters FORCE
>         $(call if_changed_dep,bindgen)
>   
>   $(obj)/uapi/uapi_generated.rs: private bindgen_target_flags = \
>       $(shell grep -Ev '^#|^$$' $(src)/bindgen_parameters)
> ++$(obj)/uapi/uapi_generated.rs: private bindgen_target_extra = ; \
> ++    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)
>