linux-kernel - Re: [PATCH v2] gendwarfksyms: Skip files with no exports

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Message-ID: <ca686233-f687-4147-b22a-72d0b0bedfcc@163.com>
Date: Mon, 10 Nov 2025 22:23:21 +0800
From: Haiyue Wang <haiyuewa@....com>
To: Miguel Ojeda <ojeda@...nel.org>, Sami Tolvanen <samitolvanen@...gle.com>,
 Alex Gaynor <alex.gaynor@...il.com>
Cc: linux-modules@...r.kernel.org, linux-kbuild@...r.kernel.org,
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
 Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org,
 linux-kernel@...r.kernel.org, patches@...ts.linux.dev, stable@...r.kernel.org
Subject: Re: [PATCH v2] gendwarfksyms: Skip files with no exports

On 11/10/2025 9:19 PM, Miguel Ojeda wrote:
> From: Sami Tolvanen <samitolvanen@...gle.com>
> 
> Starting with Rust 1.91.0 (released 2025-10-30), in upstream commit
> ab91a63d403b ("Ignore intrinsic calls in cross-crate-inlining cost model")
> [1][2], `bindings.o` stops containing DWARF debug information because the
> `Default` implementations contained `write_bytes()` calls which are now
> ignored in that cost model (note that `CLIPPY=1` does not reproduce it).
> 
> This means `gendwarfksyms` complains:
> 
>        RUSTC L rust/bindings.o
>      error: gendwarfksyms: process_module: dwarf_get_units failed: no debugging information?
> 
> There are several alternatives that would work here: conditionally
> skipping in the cases needed (but that is subtle and brittle), forcing
> DWARF generation with e.g. a dummy `static` (ugly and we may need to
> do it in several crates), skipping the call to the tool in the Kbuild
> command when there are no exports (fine) or teaching the tool to do so
> itself (simple and clean).
> 
> Thus do the last one: don't attempt to process files if we have no symbol
> versions to calculate.
> 
>    [ I used the commit log of my patch linked below since it explained the
>      root issue and expanded it a bit more to summarize the alternatives.
> 
>        - Miguel ]
> 
> Cc: stable@...r.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
> Reported-by: Haiyue Wang <haiyuewa@....com>
> Closes: https://lore.kernel.org/rust-for-linux/b8c1c73d-bf8b-4bf2-beb1-84ffdcd60547@163.com/
> Suggested-by: Miguel Ojeda <ojeda@...nel.org>
> Link: https://lore.kernel.org/rust-for-linux/CANiq72nKC5r24VHAp9oUPR1HVPqT+=0ab9N0w6GqTF-kJOeiSw@mail.gmail.com/
> Link: https://github.com/rust-lang/rust/commit/ab91a63d403b0105cacd72809cd292a72984ed99 [1]
> Link: https://github.com/rust-lang/rust/pull/145910 [2]
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> ---
>   scripts/gendwarfksyms/gendwarfksyms.c | 3 ++-
>   scripts/gendwarfksyms/gendwarfksyms.h | 2 +-
>   scripts/gendwarfksyms/symbols.c       | 4 +++-
>   3 files changed, 6 insertions(+), 3 deletions(-)
> 

Tested-by: Haiyue Wang <haiyuewa@....com>