[PATCH v4 3/6] gpu: nova-core: export Rust symbols for nova-drm

[Alexandre Courbot <acourbot@nvidia.com>]

Export nova-core's Rust symbols so nova-drm can resolve references to it
when loaded as a module.

This is done by generating declarations and EXPORT_SYMBOL_RUST_GPL()
calls for Rust global symbols using nm and compiling them into the
module as nova_core_exports.o.

This is intended to be a workaround until the build system supports Rust
cross-crate dependencies natively.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
 drivers/gpu/Makefile                      | 18 +++++++++++++++++-
 drivers/gpu/nova-core/.gitignore          |  1 +
 drivers/gpu/nova-core/nova_core_exports.c | 15 +++++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/Makefile b/drivers/gpu/Makefile
index 45e0941324fb..2f9c6101e21c 100644
--- a/drivers/gpu/Makefile
+++ b/drivers/gpu/Makefile
@@ -14,7 +14,23 @@ obj-$(CONFIG_TRACE_GPU_MEM)		+= trace/
 # system supports cross-crate dependencies natively.
 
 obj-$(CONFIG_NOVA_CORE) += nova-core.o
-nova-core-y := nova-core/nova_core.o
+nova-core-y := nova-core/nova_core.o nova-core/nova_core_exports.o
 
 obj-$(CONFIG_DRM_NOVA) += nova-drm.o
 nova-drm-y := drm/nova/nova.o
+
+# Slightly adapted from rust/Makefile's rust_exports, restricted to Rust v0
+# mangled symbols.
+rust_exports = $(NM) -p --defined-only $(1) | awk '$$2~/(T|R|D|B)/ && $$3~/^_R/ && $$3!~/_(init|cleanup)_module$$/ && $$3!~/__(pfx|cfi|odr_asan)/ { printf $(2),$$3 }'
+
+quiet_cmd_exports = EXPORTS $@
+      cmd_exports = \
+	$(call rust_exports,$<,"EXPORT_SYMBOL_RUST_GPL(%s);\n") > $@
+
+$(obj)/nova-core/exports_nova_core_generated.h: $(obj)/nova-core/nova_core.o FORCE
+	$(call if_changed,exports)
+
+targets += nova-core/exports_nova_core_generated.h
+
+$(obj)/nova-core/nova_core_exports.o: $(obj)/nova-core/exports_nova_core_generated.h
+CFLAGS_nova-core/nova_core_exports.o := -I $(objtree)/$(obj)/nova-core
diff --git a/drivers/gpu/nova-core/.gitignore b/drivers/gpu/nova-core/.gitignore
new file mode 100644
index 000000000000..7cc8318c76b1
--- /dev/null
+++ b/drivers/gpu/nova-core/.gitignore
@@ -0,0 +1 @@
+exports_nova_core_generated.h
diff --git a/drivers/gpu/nova-core/nova_core_exports.c b/drivers/gpu/nova-core/nova_core_exports.c
new file mode 100644
index 000000000000..6e80ca9792ee
--- /dev/null
+++ b/drivers/gpu/nova-core/nova_core_exports.c
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+
+/*
+ * Exports Rust symbols from the `nova_core` crate for use by dependent modules.
+ *
+ * This is a workaround until the build system supports Rust cross-module
+ * dependencies natively.
+ */
+
+#include <linux/export.h>
+
+#define EXPORT_SYMBOL_RUST_GPL(sym) extern int sym; EXPORT_SYMBOL_GPL(sym)
+
+#include "exports_nova_core_generated.h"

-- 
2.54.0