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

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 <redacted>
Signed-off-by: Matthew Maurer <redacted>
---
 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) > $@