[PATCH 15/15] kbuild: Use gendwarfksyms to generate Rust symbol versions

[Sami Tolvanen <samitolvanen@google.com>]

Use gendwarfksyms to generate symbol versions for exported Rust symbols,
and allow CONFIG_MODVERSIONS to be enabled with CONFIG_RUST, assuming the
debugging information needed by gendwarfksyms is also available.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 Makefile      |  6 ++++++
 init/Kconfig  |  2 +-
 rust/Makefile | 30 ++++++++++++++++++++++++------
 3 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/Makefile b/Makefile
index 14427547dc1e..0701917c5172 100644
--- a/Makefile
+++ b/Makefile
@@ -1344,6 +1344,12 @@ prepare: tools/bpf/resolve_btfids
 endif
 endif
 
+ifdef CONFIG_MODVERSIONS
+ifdef CONFIG_RUST
+prepare: tools/gendwarfksyms
+endif
+endif
+
 PHONY += resolve_btfids_clean
 
 resolve_btfids_O = $(abspath $(objtree))/tools/bpf/resolve_btfids
diff --git a/init/Kconfig b/init/Kconfig
index 72404c1f2157..ef29f002e932 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1903,7 +1903,7 @@ config RUST
 	depends on HAVE_RUST
 	depends on RUST_IS_AVAILABLE
 	depends on !CFI_CLANG
-	depends on !MODVERSIONS
+	depends on !MODVERSIONS || (DEBUG_INFO && !DEBUG_INFO_REDUCED && !DEBUG_INFO_SPLIT)
 	depends on !GCC_PLUGINS
 	depends on !RANDSTRUCT
 	depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
diff --git a/rust/Makefile b/rust/Makefile
index f70d5e244fee..385cdf5dc320 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -356,10 +356,11 @@ $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_extra = ;
 $(obj)/bindings/bindings_helpers_generated.rs: $(src)/helpers.c FORCE
 	$(call if_changed_dep,bindgen)
 
+rust_exports = $(NM) -p --defined-only $(1) | awk '/ (T|R|D) / { printf $(2),$(3) }'
+
 quiet_cmd_exports = EXPORTS $@
       cmd_exports = \
-	$(NM) -p --defined-only $< \
-		| awk '/ (T|R|D) / {printf "EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3}' > $@
+	$(call rust_exports,$<,"EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3) > $@
 
 $(obj)/exports_core_generated.h: $(obj)/core.o FORCE
 	$(call if_changed,exports)
@@ -420,12 +421,29 @@ ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
 		__ashlti3 __lshrti3
 endif
 
+ifdef CONFIG_MODVERSIONS
+# When module versioning is enabled, calculate symbol versions from the DWARF
+# debugging information. We can't use a source code parser like genksyms,
+# because the source files don't have information about the final structure
+# layout and emitted symbols.
+gendwarfksyms := $(objtree)/tools/gendwarfksyms/gendwarfksyms
+
+cmd_gendwarfksyms = \
+	$(call rust_exports,$@,"%s %s\n",$$1$(comma)$$3) \
+		| $(gendwarfksyms) $@ >> $(dot-target).cmd
+endif
+
+define rule_rustc_library_with_exports
+	$(call cmd_and_fixdep,rustc_library)
+	$(call cmd,gendwarfksyms)
+endef
+
 $(obj)/core.o: private skip_clippy = 1
 $(obj)/core.o: private skip_flags = -Dunreachable_pub
 $(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
 $(obj)/core.o: private rustc_target_flags = $(core-cfgs)
 $(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs FORCE
-	+$(call if_changed_dep,rustc_library)
+	+$(call if_changed_rule,rustc_library_with_exports)
 ifdef CONFIG_X86_64
 $(obj)/core.o: scripts/target.json
 endif
@@ -438,7 +456,7 @@ $(obj)/alloc.o: private skip_clippy = 1
 $(obj)/alloc.o: private skip_flags = -Dunreachable_pub
 $(obj)/alloc.o: private rustc_target_flags = $(alloc-cfgs)
 $(obj)/alloc.o: $(RUST_LIB_SRC)/alloc/src/lib.rs $(obj)/compiler_builtins.o FORCE
-	+$(call if_changed_dep,rustc_library)
+	+$(call if_changed_rule,rustc_library_with_exports)
 
 $(obj)/build_error.o: $(src)/build_error.rs $(obj)/compiler_builtins.o FORCE
 	+$(call if_changed_dep,rustc_library)
@@ -447,7 +465,7 @@ $(obj)/bindings.o: $(src)/bindings/lib.rs \
     $(obj)/compiler_builtins.o \
     $(obj)/bindings/bindings_generated.rs \
     $(obj)/bindings/bindings_helpers_generated.rs FORCE
-	+$(call if_changed_dep,rustc_library)
+	+$(call if_changed_rule,rustc_library_with_exports)
 
 $(obj)/uapi.o: $(src)/uapi/lib.rs \
     $(obj)/compiler_builtins.o \
@@ -458,6 +476,6 @@ $(obj)/kernel.o: private rustc_target_flags = --extern alloc \
     --extern build_error --extern macros --extern bindings --extern uapi
 $(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/alloc.o $(obj)/build_error.o \
     $(obj)/libmacros.so $(obj)/bindings.o $(obj)/uapi.o FORCE
-	+$(call if_changed_dep,rustc_library)
+	+$(call if_changed_rule,rustc_library_with_exports)
 
 endif # CONFIG_RUST
-- 
2.45.2.627.g7a2c4fd464-goog