linux-kernel - Re: [PATCH 1/5] objtool/rust: add one more `noreturn` Rust function for Rust 1.87.0

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Message-ID: <20250513215833.GA1353208@joelnvbox>
Date: Tue, 13 May 2025 17:58:33 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: Miguel Ojeda <ojeda@...nel.org>
Cc: 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>,
	Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
	stable@...r.kernel.org, Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, ttabi@...dia.com,
	acourbot@...dia.com, jhubbard@...dia.com, apopple@...dia.com
Subject: Re: [PATCH 1/5] objtool/rust: add one more `noreturn` Rust function
 for Rust 1.87.0

On Tue, May 13, 2025 at 02:07:57PM -0400, Joel Fernandes wrote:
> Hello Miguel,
> 
> On Fri, May 02, 2025 at 04:02:33PM +0200, Miguel Ojeda wrote:
> > Starting with Rust 1.87.0 (expected 2025-05-15), `objtool` may report:
> > 
> >     rust/core.o: warning: objtool: _R..._4core9panicking9panic_fmt() falls
> >     through to next function _R..._4core9panicking18panic_nounwind_fmt()
> > 
> >     rust/core.o: warning: objtool: _R..._4core9panicking18panic_nounwind_fmt()
> >     falls through to next function _R..._4core9panicking5panic()
> 
> We are seeing a similar issue with the patch [1]:
> 
>   RUSTC [M] drivers/gpu/nova-core/nova_core.o
> drivers/gpu/nova-core/nova_core.o: warning: objtool:
> <nova_core::vbios::PciAtBiosImage as
> core::convert::TryFrom<nova_core::vbios::BiosImageBase>>::try_from() falls
> through to next function <nova_core::vbios::FwSecBiosImage>::fwsec_header()
> 
> The code in concern is implementing try_from():
> +
> +impl TryFrom<BiosImageBase> for PciAtBiosImage {
> +    type Error = Error;
> +
> +    fn try_from(base: BiosImageBase) -> Result<Self> {
> 
> I dumped the codegen [2] for this function and at the end of the codegen, there
> is a call instruction to to the fwsec_header() function.
> 
> Any thoughts on how to fix the warning?

Btw, Danilo mentioned to me the latest Rust compiler (1.86?) does not give
this warning for that patch.

Mine is on 1.85. So if anyone else other than me is suffering from this
warning, do upgrade. :-)

thanks,

 - Joel