[PATCH v5 0/4] clean up EXPORT_SYMBOL_RUST_GPL

[PATCH v5 0/4] clean up EXPORT_SYMBOL_RUST_GPL

[Giuliano Procida]

This is a complete rework of the previous series to switch to assembly
as suggested by Gary Guo <gary@garyguo.net> in a review comment.

The first change in this series is a miniscule safety fix that will be
obsoleted once the Nova driver Rust symbol handling is itself cleaned
up.

The second and third changes switch symbol export to assembly.

The fourth change tweaks a related test file.

Giuliano Procida (4):
  kbuild: respect skip_gendwarfksyms in cmd_gensymtypes_S
  rust: convert exports.c to assembly
  gpu: nova-core: convert nova_core_exports.c to assembly
  scripts/sbom: update rust export macro in nm parser test

 drivers/gpu/Makefile                                 | 11 ++++++-----
 .../{nova_core_exports.c => nova_core_exports.S}     |  8 +++-----
 rust/Makefile                                        |  2 +-
 rust/{exports.c => exports.S}                        | 12 +++++-------
 scripts/Makefile.build                               |  4 ++--
 scripts/sbom/tests/cmd_graph/test_savedcmd_parser.py |  2 +-
 6 files changed, 18 insertions(+), 21 deletions(-)
 rename drivers/gpu/nova-core/{nova_core_exports.c => nova_core_exports.S} (62%)
 rename rust/{exports.c => exports.S} (72%)

-- 
2.56.0.567.gdb80ae8cd5-goog

[PATCH v5 1/4] kbuild: respect skip_gendwarfksyms in cmd_gensymtypes_S

[Giuliano Procida]

Commit 9c3681f9b9fd ("kbuild: Add gendwarfksyms as an alternative to
genksyms") added `skip_gendwarfksyms` handling to `cmd_gensymtypes_c` so
that `rust/exports.o` could skip symbol version generation, as CRCs are
computed directly from the defining Rust and helper object files.

`cmd_gensymtypes_S` is meant to mirror `cmd_gensymtypes_c`, as noted in
the comments above both definitions, but omitted the
`skip_gendwarfksyms` check. Respect `skip_gendwarfksyms` in
`cmd_gensymtypes_S` as well so that `rust/exports.c` can be converted to
assembly without `getasmexports` attempting to compile undeclared Rust
and helper symbols against `<asm/asm-prototypes.h>` when
`CONFIG_MODVERSIONS` is enabled.

Signed-off-by: Giuliano Procida <gprocida@google.com>
---
 scripts/Makefile.build | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 6127feb970c6..873a9ed62a18 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -428,11 +428,11 @@ getasmexports =								\
      $(call getexportsymbols,EXPORT_SYMBOL(\1);) ; }
 
 ifdef CONFIG_GENDWARFKSYMS
-cmd_gensymtypes_S =							\
+cmd_gensymtypes_S = $(if $(skip_gendwarfksyms),,			\
 	$(getasmexports) |						\
 	$(CC) $(c_flags) -c -o $(@:.o=.gendwarfksyms.o) -xc -;		\
 	$(call getexportsymbols,\1) |					\
-	$(gendwarfksyms) $(@:.o=.gendwarfksyms.o)
+	$(gendwarfksyms) $(@:.o=.gendwarfksyms.o))
 else
 cmd_gensymtypes_S =							\
 	$(getasmexports) |						\
-- 
2.56.0.567.gdb80ae8cd5-goog

[PATCH v5 2/4] rust: convert exports.c to assembly

[Giuliano Procida]

Previously, `rust/exports.c` defined `EXPORT_SYMBOL_RUST_GPL(sym)` with
`extern int sym;` so that it could invoke the C `EXPORT_SYMBOL_GPL(sym)`
macro, which requires `sym` to be a declared C identifier in scope for
`typeof(sym)`, `__ADDRESSABLE(sym)` and `__GENDWARFKSYMS_EXPORT(sym)`.

This caused the C compiler to emit DWARF debug information in
`rust/exports.o` describing every exported Rust and helper symbol,
functions and data alike, as a C `int` variable. Those bogus `int` DWARF
entries ended up in `vmlinux`, conflicting with the true DWARF types
emitted by `rustc` and confusing debuggers and ABI analysis tools.

Convert `rust/exports.c` to `rust/exports.S` and emit
`EXPORT_SYMBOL_GPL(sym)` directly. Under `__ASSEMBLY__`,
`<linux/export.h>` expands `EXPORT_SYMBOL_GPL(sym)` straight to
`___EXPORT_SYMBOL(sym, "GPL", ...)` without requiring symbol
declarations or emitting bogus DWARF entries, while also avoiding a C
compilation step.

Signed-off-by: Giuliano Procida <gprocida@google.com>
---
 rust/Makefile                 |  2 +-
 rust/{exports.c => exports.S} | 12 +++++-------
 2 files changed, 6 insertions(+), 8 deletions(-)
 rename rust/{exports.c => exports.S} (72%)

diff --git a/rust/Makefile b/rust/Makefile
index 0ac9ab28cc2b..2e5f5a84bb24 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -564,7 +564,7 @@ rust_exports = $(NM) -p --defined-only $(1) | awk '$$2~/(T|R|D|B)/ && $$3!~/__(p
 
 quiet_cmd_exports = EXPORTS $@
       cmd_exports = \
-	$(call rust_exports,$<,"EXPORT_SYMBOL_RUST_GPL(%s);\n") > $@
+	$(call rust_exports,$<,"EXPORT_SYMBOL_GPL(%s)\n") > $@
 
 $(obj)/exports_core_generated.h: $(obj)/core.o FORCE
 	$(call if_changed,exports)
diff --git a/rust/exports.c b/rust/exports.S
similarity index 72%
rename from rust/exports.c
rename to rust/exports.S
index 1b52460b0f4e..e1a6923081fa 100644
--- a/rust/exports.c
+++ b/rust/exports.S
@@ -1,11 +1,11 @@
-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * A hack to export Rust symbols for loadable modules without having to redo
  * the entire `include/linux/export.h` logic in Rust.
  *
  * This requires Rust's new/future `v0` mangling scheme because the default one
- * ("legacy") uses invalid characters for C identifiers (thus we cannot use the
- * `EXPORT_SYMBOL_*` macros).
+ * ("legacy") uses invalid characters for C identifiers (thus we could not use
+ * the `EXPORT_SYMBOL_*` macros).
  *
  * All symbols are exported as GPL-only to guarantee no GPL-only feature is
  * accidentally exposed.
@@ -13,8 +13,6 @@
 
 #include <linux/export.h>
 
-#define EXPORT_SYMBOL_RUST_GPL(sym) extern int sym; EXPORT_SYMBOL_GPL(sym)
-
 #include "exports_core_generated.h"
 #include "exports_bindings_generated.h"
 #include "exports_kernel_generated.h"
@@ -23,7 +21,7 @@
 #include "exports_helpers_generated.h"
 #endif
 
-// For modules using `rust/build_error.rs`.
+/* For modules using `rust/build_error.rs`. */
 #ifdef CONFIG_RUST_BUILD_ASSERT_ALLOW
-EXPORT_SYMBOL_RUST_GPL(rust_build_error);
+EXPORT_SYMBOL_GPL(rust_build_error)
 #endif
-- 
2.56.0.567.gdb80ae8cd5-goog

Re: [PATCH v5 2/4] rust: convert exports.c to assembly

[Miguel Ojeda]

On Thu, Nov 12, 2026 at 1:15 PM Giuliano Procida <gprocida@google.com> wrote:
>
> Previously, `rust/exports.c` defined `EXPORT_SYMBOL_RUST_GPL(sym)` with
> `extern int sym;` so that it could invoke the C `EXPORT_SYMBOL_GPL(sym)`
> macro, which requires `sym` to be a declared C identifier in scope for
> `typeof(sym)`, `__ADDRESSABLE(sym)` and `__GENDWARFKSYMS_EXPORT(sym)`.
>
> This caused the C compiler to emit DWARF debug information in
> `rust/exports.o` describing every exported Rust and helper symbol,
> functions and data alike, as a C `int` variable. Those bogus `int` DWARF
> entries ended up in `vmlinux`, conflicting with the true DWARF types
> emitted by `rustc` and confusing debuggers and ABI analysis tools.
>
> Convert `rust/exports.c` to `rust/exports.S` and emit
> `EXPORT_SYMBOL_GPL(sym)` directly. Under `__ASSEMBLY__`,
> `<linux/export.h>` expands `EXPORT_SYMBOL_GPL(sym)` straight to
> `___EXPORT_SYMBOL(sym, "GPL", ...)` without requiring symbol
> declarations or emitting bogus DWARF entries, while also avoiding a C
> compilation step.
>
> Signed-off-by: Giuliano Procida <gprocida@google.com>

I guess Suggested-by: Gary?

Cheers,
Miguel

[PATCH v5 3/4] gpu: nova-core: convert nova_core_exports.c to assembly

[Giuliano Procida]

Like `rust/exports.c` before it, `nova_core_exports.c` defined
`EXPORT_SYMBOL_RUST_GPL(sym)` with `extern int sym;` so that it could
invoke the C `EXPORT_SYMBOL_GPL(sym)` macro. This emitted bogus `int`
DWARF debug information in `nova_core_exports.o` and `nova-core.ko` for
every exported Rust symbol, conflicting with the DWARF types emitted by
`rustc`.

Convert `nova_core_exports.c` to `nova_core_exports.S`, emit
`EXPORT_SYMBOL_GPL(sym)` directly in `exports_nova_core_generated.h`
and switch the include path and `MODVERSIONS` symbol-versioning hook in
`drivers/gpu/Makefile` from the `.c` rules (`CFLAGS_*` /
`cmd_gensymtypes_c`) to the `.S` rules (`AFLAGS_*` /
`cmd_gensymtypes_S`).

Also set `private cmd_gen_symversions_S = $(call gen_symversions,S)`
under `CONFIG_MODVERSIONS`. Kbuild normally defines
`cmd_gen_symversions_S` only under `CONFIG_ASM_MODVERSIONS` (which
requires `<asm/asm-prototypes.h>` and is not selected on 32-bit `arm`),
whereas `nova_core_exports.o` generates CRCs directly from `nova_core.o`
via `gendwarfksyms` without needing `<asm/asm-prototypes.h>`. Although
`NOVA_CORE` currently depends on `64BIT`, keeping the `MODVERSIONS`
override self-contained avoids an implicit `CONFIG_ASM_MODVERSIONS`
dependency if `64BIT` is ever relaxed or the pattern is reused by
another Rust module.

This removes the last definition and use of `EXPORT_SYMBOL_RUST_GPL`.

Signed-off-by: Giuliano Procida <gprocida@google.com>
---
 drivers/gpu/Makefile                                  | 11 ++++++-----
 .../{nova_core_exports.c => nova_core_exports.S}      |  8 +++-----
 2 files changed, 9 insertions(+), 10 deletions(-)
 rename drivers/gpu/nova-core/{nova_core_exports.c => nova_core_exports.S} (62%)

diff --git a/drivers/gpu/Makefile b/drivers/gpu/Makefile
index e372fc02139f..49205525d2a5 100644
--- a/drivers/gpu/Makefile
+++ b/drivers/gpu/Makefile
@@ -36,7 +36,7 @@ rust_needed_exports = \
 
 quiet_cmd_exports = EXPORTS $@
       cmd_exports = \
-	$(call rust_needed_exports,$<,$(nova-core-export-deps),EXPORT_SYMBOL_RUST_GPL(%s);\n) > $@
+	$(call rust_needed_exports,$<,$(nova-core-export-deps),EXPORT_SYMBOL_GPL(%s)\n) > $@
 
 $(obj)/nova-core/exports_nova_core_generated.h: $(obj)/nova-core/nova_core.o $(nova-core-export-deps) FORCE
 	$(call if_changed,exports)
@@ -44,12 +44,13 @@ $(obj)/nova-core/exports_nova_core_generated.h: $(obj)/nova-core/nova_core.o $(n
 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
+AFLAGS_nova-core/nova_core_exports.o := -I $(objtree)/$(obj)/nova-core
 
 ifdef CONFIG_MODVERSIONS
-# The C export shim declares Rust symbols as `extern int`, so reuse its export
-# list but generate symbol CRCs from the Rust object instead of the shim's DWARF.
-$(obj)/nova-core/nova_core_exports.o: private cmd_gensymtypes_c = \
+# The assembly export shim has no DWARF type info for Rust symbols, so reuse
+# its export list but generate symbol CRCs from the Rust object.
+$(obj)/nova-core/nova_core_exports.o: private cmd_gen_symversions_S = $(call gen_symversions,S)
+$(obj)/nova-core/nova_core_exports.o: private cmd_gensymtypes_S = \
 	$(call getexportsymbols,\1) | \
 	$(objtree)/scripts/gendwarfksyms/gendwarfksyms \
 		$(if $(KBUILD_GENDWARFKSYMS_STABLE), --stable) \
diff --git a/drivers/gpu/nova-core/nova_core_exports.c b/drivers/gpu/nova-core/nova_core_exports.S
similarity index 62%
rename from drivers/gpu/nova-core/nova_core_exports.c
rename to drivers/gpu/nova-core/nova_core_exports.S
index 6e80ca9792ee..90a9f709ed38 100644
--- a/drivers/gpu/nova-core/nova_core_exports.c
+++ b/drivers/gpu/nova-core/nova_core_exports.S
@@ -1,7 +1,7 @@
-// SPDX-License-Identifier: GPL-2.0
-// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
-
+/* 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
@@ -10,6 +10,4 @@
 
 #include <linux/export.h>
 
-#define EXPORT_SYMBOL_RUST_GPL(sym) extern int sym; EXPORT_SYMBOL_GPL(sym)
-
 #include "exports_nova_core_generated.h"
-- 
2.56.0.567.gdb80ae8cd5-goog

[PATCH v5 4/4] scripts/sbom: update rust export macro in nm parser test

[Giuliano Procida]

Update the sample `rust/Makefile` export generation command in `test_nm`
to match the conversion from `EXPORT_SYMBOL_RUST_GPL(%s);` to
`EXPORT_SYMBOL_GPL(%s)`.

Signed-off-by: Giuliano Procida <gprocida@google.com>
---
 scripts/sbom/tests/cmd_graph/test_savedcmd_parser.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/sbom/tests/cmd_graph/test_savedcmd_parser.py b/scripts/sbom/tests/cmd_graph/test_savedcmd_parser.py
index 93787a1cd156..4f7ee1142cd8 100644
--- a/scripts/sbom/tests/cmd_graph/test_savedcmd_parser.py
+++ b/scripts/sbom/tests/cmd_graph/test_savedcmd_parser.py
@@ -214,7 +214,7 @@ class TestSavedCmdParser(unittest.TestCase):
 
     # nm command tests
     def test_nm(self):
-        cmd = """llvm-nm -p --defined-only rust/core.o | awk '$$2~/(T|R|D|B)/ && $$3!~/__(pfx|cfi|odr_asan)/ { printf "EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3 }' > rust/exports_core_generated.h"""
+        cmd = """llvm-nm -p --defined-only rust/core.o | awk '$$2~/(T|R|D|B)/ && $$3!~/__(pfx|cfi|odr_asan)/ { printf "EXPORT_SYMBOL_GPL(%s)\n",$$3 }' > rust/exports_core_generated.h"""
         expected = "rust/core.o"
         self._assert_parsing(cmd, expected)
 
-- 
2.56.0.567.gdb80ae8cd5-goog

Re: [PATCH v5 0/4] clean up EXPORT_SYMBOL_RUST_GPL

[Giuliano Procida]

Oops.

On Thu, 12 Nov 2026 at 12:15, Giuliano Procida <gprocida@google.com> wrote:
>
> This is a complete rework of the previous series to switch to assembly
> as suggested by Gary Guo <gary@garyguo.net> in a review comment.
>
> The first change in this series is a miniscule safety fix that will be
> obsoleted once the Nova driver Rust symbol handling is itself cleaned
> up.

Sorry, that's a lie. This is the prep work for the next two changes.

The tiny safety fix relating to `arm` is in the nova-core change itself.

> The second and third changes switch symbol export to assembly.
>
> The fourth change tweaks a related test file.
>
> Giuliano Procida (4):
>   kbuild: respect skip_gendwarfksyms in cmd_gensymtypes_S
>   rust: convert exports.c to assembly
>   gpu: nova-core: convert nova_core_exports.c to assembly
>   scripts/sbom: update rust export macro in nm parser test
>
>  drivers/gpu/Makefile                                 | 11 ++++++-----
>  .../{nova_core_exports.c => nova_core_exports.S}     |  8 +++-----
>  rust/Makefile                                        |  2 +-
>  rust/{exports.c => exports.S}                        | 12 +++++-------
>  scripts/Makefile.build                               |  4 ++--
>  scripts/sbom/tests/cmd_graph/test_savedcmd_parser.py |  2 +-
>  6 files changed, 18 insertions(+), 21 deletions(-)
>  rename drivers/gpu/nova-core/{nova_core_exports.c => nova_core_exports.S} (62%)
>  rename rust/{exports.c => exports.S} (72%)
>
> --
> 2.56.0.567.gdb80ae8cd5-goog
>