Re: [PATCH v7 3/3] rust: Use gendwarfksyms + extended modversions for CONFIG_MODVERSIONS

[Sami Tolvanen <samitolvanen@google.com>]

On Wed, Oct 23, 2024 at 02:31:30AM +0000, Matthew Maurer 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 | 32 ++++++++++++++++++++++++++++++--
>  2 files changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index 530a382ee0feb391b4717abdba3672e584a462d0..f5cce579f29b2ed89e97f8075a3bf70e32e71ad0 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1942,7 +1942,8 @@ config RUST
>  	bool "Rust support"
>  	depends on HAVE_RUST
>  	depends on RUST_IS_AVAILABLE
> -	depends on !MODVERSIONS
> +	select EXTENDED_MODVERSIONS if MODVERSIONS
> +	depends on (GENDWARFKSYMS || !MODVERSIONS)

Nit: `depends on !MODVERSIONS || GENDWARFKSYMS` would match the
convention used below.

> +cmd_gendwarfksyms = $(if $(skip_gendwarfksyms),, \
> +	$(call rust_exports,$@,"%s\n",$$3) | \
> +	scripts/gendwarfksyms/gendwarfksyms \
> +		$(if $(KBUILD_SYMTYPES), --symtypes $(@:.o=.symtypes),) \
> +		$@ >> $(dot-target).cmd)

Note that Petr suggested adding a KBUILD_ flag for passing the
--stable parameter to gendwarfksyms, which I think would be useful,
so once I send out v5 of that series, we'll have to update this to
also use the parameter when processing Rust objects:

https://lore.kernel.org/linux-modules/8017c328-f039-46c3-b472-f203cd6e2cfe@suse.com/

Sami