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

Masahiro Yamada
2025-01-11T02:26:13Z

On Sat, Jan 4, 2025 at 2:37 AM Matthew Maurer <mmaurer@google.com> wrote:
>
> 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) > $@

I noticed a nit:

Both of the two callsites of rust_exports pass
'$$3' to the last parameter instead of hardcoding it.

Is it a flexibility for future extensions?

I cannot think of any other use except for printing
the third column, i.e. symbol name.

--
Best Regards
Masahiro Yamada