[PATCH v13 5/5] rust: Use gendwarfksyms + extended modversions for CONFIG_MODVERSIONS

Matthew Maurer
2025-01-03T17:37:13Z

From: Sami Tolvanen <samitolvanen@google.com>

Previously, two things stopped Rust from using MODVERSIONS:
1. Rust symbols are occasionally too long to be represented in the
original versions table
2. Rust types cannot be properly hashed by the existing genksyms
approach because:
* Looking up type definitions in Rust is more complex than C
* Type layout is potentially dependent on the compiler in Rust,
not just the source type declaration.

CONFIG_EXTENDED_MODVERSIONS addresses the first point, and
CONFIG_GENDWARFKSYMS the second. If Rust wants to use MODVERSIONS, allow
it to do so by selecting both features.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Co-developed-by: Matthew Maurer <mmaurer@google.com>
Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
init/Kconfig | 3 ++-
rust/Makefile | 34 ++++++++++++++++++++++++++++++++--
2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index c1f9eb3d5f2e892e977ba1425599502dc830f552..b60acfd9431e0ac2bf401ecb6523b5104ad31150 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1959,7 +1959,8 @@ config RUST
bool "Rust support"
depends on HAVE_RUST
depends on RUST_IS_AVAILABLE
- depends on !MODVERSIONS
+ select EXTENDED_MODVERSIONS if MODVERSIONS
+ depends on !MODVERSIONS || GENDWARFKSYMS
depends on !GCC_PLUGIN_RANDSTRUCT
depends on !RANDSTRUCT
depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
diff --git a/rust/Makefile b/rust/Makefile
index a40a3936126d603836e0ec9b42a1285916b60e45..80f970ad81f7989afe5ff2b5f633f50feb7f6006 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -329,10 +329,11 @@ $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_extra = ;
$(obj)/bindings/bindings_helpers_generated.rs: $(src)/helpers/helpers.c FORCE
$(call if_changed_dep,bindgen)

+rust_exports = $(NM) -p --defined-only $(1) | awk '$$2~/(T|R|D|B)/ && $$3!~/__cfi/ { printf $(2),$(3) }'
+
quiet_cmd_exports = EXPORTS $@
cmd_exports = \
- $(NM) -p --defined-only $< \
- | awk '$$2~/(T|R|D|B)/ && $$3!~/__cfi/ {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
$(call if_changed,exports)
@@ -401,11 +402,36 @@ ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
__ashlti3 __lshrti3
endif

+ifdef CONFIG_MODVERSIONS
+cmd_gendwarfksyms = $(if $(skip_gendwarfksyms),, \
+ $(call rust_exports,$@,"%s\n",$$3) | \
+ scripts/gendwarfksyms/gendwarfksyms \
+ $(if $(KBUILD_GENDWARFKSYMS_STABLE), --stable) \
+ $(if $(KBUILD_SYMTYPES), --symtypes $(@:.o=.symtypes),) \
+ $@ >> $(dot-target).cmd)
+endif
+
define rule_rustc_library
$(call cmd_and_fixdep,rustc_library)
$(call cmd,gen_objtooldep)
+ $(call cmd,gendwarfksyms)
endef

+define rule_rust_cc_library
+ $(call if_changed_rule,cc_o_c)
+ $(call cmd,force_checksrc)
+ $(call cmd,gendwarfksyms)
+endef
+
+# helpers.o uses the same export mechanism as Rust libraries, so ensure symbol
+# versions are calculated for the helpers too.
+$(obj)/helpers/helpers.o: $(src)/helpers/helpers.c $(recordmcount_source) FORCE
+ +$(call if_changed_rule,rust_cc_library)
+
+# Disable symbol versioning for exports.o to avoid conflicts with the actual
+# symbol versions generated from Rust objects.
+$(obj)/exports.o: private skip_gendwarfksyms = 1
+
$(obj)/core.o: private skip_clippy = 1
$(obj)/core.o: private skip_flags = -Wunreachable_pub
$(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
@@ -417,13 +443,16 @@ ifneq ($(or $(CONFIG_X86_64),$(CONFIG_X86_32)),)
$(obj)/core.o: scripts/target.json
endif

+$(obj)/compiler_builtins.o: private skip_gendwarfksyms = 1
$(obj)/compiler_builtins.o: private rustc_objcopy = -w -W '__*'
$(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
+$(call if_changed_rule,rustc_library)

+$(obj)/build_error.o: private skip_gendwarfksyms = 1
$(obj)/build_error.o: $(src)/build_error.rs $(obj)/compiler_builtins.o FORCE
+$(call if_changed_rule,rustc_library)

+$(obj)/ffi.o: private skip_gendwarfksyms = 1
$(obj)/ffi.o: $(src)/ffi.rs $(obj)/compiler_builtins.o FORCE
+$(call if_changed_rule,rustc_library)

@@ -435,6 +464,7 @@ $(obj)/bindings.o: $(src)/bindings/lib.rs \
+$(call if_changed_rule,rustc_library)

$(obj)/uapi.o: private rustc_target_flags = --extern ffi
+$(obj)/uapi.o: private skip_gendwarfksyms = 1
$(obj)/uapi.o: $(src)/uapi/lib.rs \
$(obj)/ffi.o \
$(obj)/uapi/uapi_generated.rs FORCE

--
2.47.1.613.gc27f4b7a9f-goog