linux-kernel - Re: [PATCH v13 5/5] rust: Use gendwarfksyms + extended modversions for CONFIG

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Message-ID: <CAK7LNATGw-m_dcdjTBHsFwCZh7mTt8q8yNZQ7VFP=hMU8NvUvg@mail.gmail.com>
Date: Sat, 11 Jan 2025 11:25:35 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Matthew Maurer <mmaurer@...gle.com>
Cc: Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, 
	Christophe Leroy <christophe.leroy@...roup.eu>, Naveen N Rao <naveen@...nel.org>, 
	Madhavan Srinivasan <maddy@...ux.ibm.com>, Luis Chamberlain <mcgrof@...nel.org>, 
	Petr Pavlu <petr.pavlu@...e.com>, Sami Tolvanen <samitolvanen@...gle.com>, 
	Daniel Gomez <da.gomez@...sung.com>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
	Jonathan Corbet <corbet@....net>, linuxppc-dev@...ts.ozlabs.org, 
	linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v13 5/5] rust: Use gendwarfksyms + extended modversions
 for CONFIG_MODVERSIONS

On Sat, Jan 4, 2025 at 2:37 AM Matthew Maurer <mmaurer@...gle.com> wrote:
>
> From: Sami Tolvanen <samitolvanen@...gle.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@...gle.com>
> Co-developed-by: Matthew Maurer <mmaurer@...gle.com>
> Signed-off-by: Matthew Maurer <mmaurer@...gle.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