[PATCH 0/2] Rust fixes for the upcoming 1.89 release

[PATCH 0/2] Rust fixes for the upcoming 1.89 release

[Miguel Ojeda]

A couple fixes for the upcoming 1.89.0 release, currently in beta.

With this, current nightly (1.90) gets also clean.

Miguel Ojeda (2):
  objtool/rust: add one more `noreturn` Rust function for Rust 1.89.0
  rust: use `#[used(compiler)]` to fix build and `modpost` with Rust >=
    1.89.0

 rust/Makefile           |  1 +
 rust/kernel/firmware.rs |  2 +-
 rust/kernel/kunit.rs    |  2 +-
 rust/kernel/lib.rs      |  3 +++
 rust/macros/module.rs   | 10 +++++-----
 scripts/Makefile.build  |  3 ++-
 tools/objtool/check.c   |  1 +
 7 files changed, 14 insertions(+), 8 deletions(-)


base-commit: fe49aae0fcb348b656bbde2eb1d1c75d8a1a5c3c
--
2.50.1

[PATCH 1/2] objtool/rust: add one more `noreturn` Rust function for Rust 1.89.0

[Miguel Ojeda]

Starting with Rust 1.89.0 (expected 2025-08-07), under
`CONFIG_RUST_DEBUG_ASSERTIONS=y`, `objtool` may report:

    rust/kernel.o: warning: objtool: _R..._6kernel4pageNtB5_4Page8read_raw()
    falls through to next function _R..._6kernel4pageNtB5_4Page9write_raw()

(and many others) due to calls to the `noreturn` symbol:

    core::panicking::panic_nounwind_fmt

Thus add the mangled one to the list so that `objtool` knows it is
actually `noreturn`.

See commit 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions")
for more details.

Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 tools/objtool/check.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f23bdda737aa..3257eefc41ed 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -224,6 +224,7 @@ static bool is_rust_noreturn(const struct symbol *func)
 	       str_ends_with(func->name, "_4core9panicking14panic_explicit")				||
 	       str_ends_with(func->name, "_4core9panicking14panic_nounwind")				||
 	       str_ends_with(func->name, "_4core9panicking18panic_bounds_check")			||
+	       str_ends_with(func->name, "_4core9panicking18panic_nounwind_fmt")			||
 	       str_ends_with(func->name, "_4core9panicking19assert_failed_inner")			||
 	       str_ends_with(func->name, "_4core9panicking30panic_null_pointer_dereference")		||
 	       str_ends_with(func->name, "_4core9panicking36panic_misaligned_pointer_dereference")	||
-- 
2.50.1

[PATCH 2/2] rust: use `#[used(compiler)]` to fix build and `modpost` with Rust >= 1.89.0

[Miguel Ojeda]

Starting with Rust 1.89.0 (expected 2025-08-07), the Rust compiler fails
to build the `rusttest` target due to undefined references such as:

    kernel...-cgu.0:(.text....+0x116): undefined reference to
    `rust_helper_kunit_get_current_test'

Moreover, tooling like `modpost` gets confused:

    WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/nova/nova.o
    ERROR: modpost: missing MODULE_LICENSE() in drivers/gpu/nova-core/nova_core.o

The reason behind both issues is that the Rust compiler will now [1]
treat `#[used]` as `#[used(linker)]` instead of `#[used(compiler)]`
for our targets. This means that the retain section flag (`R`,
`SHF_GNU_RETAIN`) will be used and that they will be marked as `unique`
too, with different IDs. In turn, that means we end up with undefined
references that did not get discarded in `rusttest` and that multiple
`.modinfo` sections are generated, which confuse tooling like `modpost`
because they only expect one.

Thus start using `#[used(compiler)]` to keep the previous behavior
and to be explicit about what we want. Sadly, it is an unstable feature
(`used_with_arg`) [2] -- we will talk to upstream Rust about it. The good
news is that it has been available for a long time (Rust >= 1.60) [3].

The changes should also be fine for previous Rust versions, since they
behave the same way as before [4].

Alternatively, we could use `#[no_mangle]` or `#[export_name = ...]`
since those still behave like `#[used(compiler)]`, but of course it is
not really what we want to express, and it requires other changes to
avoid symbol conflicts.

Cc: Björn Roy Baron <bjorn3_gh@protonmail.com>
Cc: David Wood <david@davidtw.co>
Cc: Wesley Wiser <wwiser@gmail.com>
Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
Link: https://github.com/rust-lang/rust/pull/140872 [1]
Link: https://github.com/rust-lang/rust/issues/93798 [2]
Link: https://github.com/rust-lang/rust/pull/91504 [3]
Link: https://godbolt.org/z/sxzWTMfzW [4]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/Makefile           |  1 +
 rust/kernel/firmware.rs |  2 +-
 rust/kernel/kunit.rs    |  2 +-
 rust/kernel/lib.rs      |  3 +++
 rust/macros/module.rs   | 10 +++++-----
 scripts/Makefile.build  |  3 ++-
 6 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/rust/Makefile b/rust/Makefile
index 27dec7904c3a..115b63b7d1e3 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -194,6 +194,7 @@ quiet_cmd_rustdoc_test = RUSTDOC T $<
 	RUST_MODFILE=test.rs \
 	OBJTREE=$(abspath $(objtree)) \
 	$(RUSTDOC) --test $(rust_common_flags) \
+		-Zcrate-attr='feature(used_with_arg)' \
 		@$(objtree)/include/generated/rustc_cfg \
 		$(rustc_target_flags) $(rustdoc_test_target_flags) \
 		$(rustdoc_test_quiet) \
diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
index 2494c96e105f..4fe621f35716 100644
--- a/rust/kernel/firmware.rs
+++ b/rust/kernel/firmware.rs
@@ -202,7 +202,7 @@ macro_rules! module_firmware {
             };
 
             #[link_section = ".modinfo"]
-            #[used]
+            #[used(compiler)]
             static __MODULE_FIRMWARE: [u8; $($builder)*::create(__MODULE_FIRMWARE_PREFIX)
                 .build_length()] = $($builder)*::create(__MODULE_FIRMWARE_PREFIX).build();
         };
diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
index 4b8cdcb21e77..b9e65905e121 100644
--- a/rust/kernel/kunit.rs
+++ b/rust/kernel/kunit.rs
@@ -302,7 +302,7 @@ macro_rules! kunit_unsafe_test_suite {
                     is_init: false,
                 };
 
-            #[used]
+            #[used(compiler)]
             #[allow(unused_unsafe)]
             #[cfg_attr(not(target_os = "macos"), link_section = ".kunit_test_suites")]
             static mut KUNIT_TEST_SUITE_ENTRY: *const ::kernel::bindings::kunit_suite =
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 6b4774b2b1c3..e13d6ed88fa6 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -34,6 +34,9 @@
 // Expected to become stable.
 #![feature(arbitrary_self_types)]
 //
+// To be determined.
+#![feature(used_with_arg)]
+//
 // `feature(derive_coerce_pointee)` is expected to become stable. Before Rust
 // 1.84.0, it did not exist, so enable the predecessor features.
 #![cfg_attr(CONFIG_RUSTC_HAS_COERCE_POINTEE, feature(derive_coerce_pointee))]
diff --git a/rust/macros/module.rs b/rust/macros/module.rs
index 2ddd2eeb2852..75efc6eeeafc 100644
--- a/rust/macros/module.rs
+++ b/rust/macros/module.rs
@@ -57,7 +57,7 @@ fn emit_base(&mut self, field: &str, content: &str, builtin: bool) {
                 {cfg}
                 #[doc(hidden)]
                 #[cfg_attr(not(target_os = \"macos\"), link_section = \".modinfo\")]
-                #[used]
+                #[used(compiler)]
                 pub static __{module}_{counter}: [u8; {length}] = *{string};
             ",
             cfg = if builtin {
@@ -249,7 +249,7 @@ mod __module_init {{
                     // key or a new section. For the moment, keep it simple.
                     #[cfg(MODULE)]
                     #[doc(hidden)]
-                    #[used]
+                    #[used(compiler)]
                     static __IS_RUST_MODULE: () = ();
 
                     static mut __MOD: ::core::mem::MaybeUninit<{type_}> =
@@ -273,7 +273,7 @@ mod __module_init {{
 
                     #[cfg(MODULE)]
                     #[doc(hidden)]
-                    #[used]
+                    #[used(compiler)]
                     #[link_section = \".init.data\"]
                     static __UNIQUE_ID___addressable_init_module: unsafe extern \"C\" fn() -> i32 = init_module;
 
@@ -293,7 +293,7 @@ mod __module_init {{
 
                     #[cfg(MODULE)]
                     #[doc(hidden)]
-                    #[used]
+                    #[used(compiler)]
                     #[link_section = \".exit.data\"]
                     static __UNIQUE_ID___addressable_cleanup_module: extern \"C\" fn() = cleanup_module;
 
@@ -303,7 +303,7 @@ mod __module_init {{
                     #[cfg(not(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS))]
                     #[doc(hidden)]
                     #[link_section = \"{initcall_section}\"]
-                    #[used]
+                    #[used(compiler)]
                     pub static __{ident}_initcall: extern \"C\" fn() ->
                         ::kernel::ffi::c_int = __{ident}_init;
 
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index a6461ea411f7..ba71b27aa363 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -312,10 +312,11 @@ $(obj)/%.lst: $(obj)/%.c FORCE
 #   - Stable since Rust 1.82.0: `feature(asm_const)`, `feature(raw_ref_op)`.
 #   - Stable since Rust 1.87.0: `feature(asm_goto)`.
 #   - Expected to become stable: `feature(arbitrary_self_types)`.
+#   - To be determined: `feature(used_with_arg)`.
 #
 # Please see https://github.com/Rust-for-Linux/linux/issues/2 for details on
 # the unstable features in use.
-rust_allowed_features := asm_const,asm_goto,arbitrary_self_types,lint_reasons,raw_ref_op
+rust_allowed_features := asm_const,asm_goto,arbitrary_self_types,lint_reasons,raw_ref_op,used_with_arg
 
 # `--out-dir` is required to avoid temporaries being created by `rustc` in the
 # current working directory, which may be not accessible in the out-of-tree
-- 
2.50.1

Re: [PATCH 1/2] objtool/rust: add one more `noreturn` Rust function for Rust 1.89.0

[Peter Zijlstra]

On Sat, Jul 12, 2025 at 06:01:02PM +0200, Miguel Ojeda wrote:
> Starting with Rust 1.89.0 (expected 2025-08-07), under
> `CONFIG_RUST_DEBUG_ASSERTIONS=y`, `objtool` may report:
> 
>     rust/kernel.o: warning: objtool: _R..._6kernel4pageNtB5_4Page8read_raw()
>     falls through to next function _R..._6kernel4pageNtB5_4Page9write_raw()
> 
> (and many others) due to calls to the `noreturn` symbol:
> 
>     core::panicking::panic_nounwind_fmt
> 
> Thus add the mangled one to the list so that `objtool` knows it is
> actually `noreturn`.
> 
> See commit 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions")
> for more details.
> 
> Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
> Cc: Josh Poimboeuf <jpoimboe@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

> ---
>  tools/objtool/check.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index f23bdda737aa..3257eefc41ed 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -224,6 +224,7 @@ static bool is_rust_noreturn(const struct symbol *func)
>  	       str_ends_with(func->name, "_4core9panicking14panic_explicit")				||
>  	       str_ends_with(func->name, "_4core9panicking14panic_nounwind")				||
>  	       str_ends_with(func->name, "_4core9panicking18panic_bounds_check")			||
> +	       str_ends_with(func->name, "_4core9panicking18panic_nounwind_fmt")			||
>  	       str_ends_with(func->name, "_4core9panicking19assert_failed_inner")			||
>  	       str_ends_with(func->name, "_4core9panicking30panic_null_pointer_dereference")		||
>  	       str_ends_with(func->name, "_4core9panicking36panic_misaligned_pointer_dereference")	||

Just having "_4core9panicking" substring is not sufficient?

Re: [PATCH 1/2] objtool/rust: add one more `noreturn` Rust function for Rust 1.89.0

[Alice Ryhl]

On Mon, Jul 14, 2025 at 10:46 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Sat, Jul 12, 2025 at 06:01:02PM +0200, Miguel Ojeda wrote:
> > Starting with Rust 1.89.0 (expected 2025-08-07), under
> > `CONFIG_RUST_DEBUG_ASSERTIONS=y`, `objtool` may report:
> >
> >     rust/kernel.o: warning: objtool: _R..._6kernel4pageNtB5_4Page8read_raw()
> >     falls through to next function _R..._6kernel4pageNtB5_4Page9write_raw()
> >
> > (and many others) due to calls to the `noreturn` symbol:
> >
> >     core::panicking::panic_nounwind_fmt
> >
> > Thus add the mangled one to the list so that `objtool` knows it is
> > actually `noreturn`.
> >
> > See commit 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions")
> > for more details.
> >
> > Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
> > Cc: Josh Poimboeuf <jpoimboe@kernel.org>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>
> > ---
> >  tools/objtool/check.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> > index f23bdda737aa..3257eefc41ed 100644
> > --- a/tools/objtool/check.c
> > +++ b/tools/objtool/check.c
> > @@ -224,6 +224,7 @@ static bool is_rust_noreturn(const struct symbol *func)
> >              str_ends_with(func->name, "_4core9panicking14panic_explicit")                            ||
> >              str_ends_with(func->name, "_4core9panicking14panic_nounwind")                            ||
> >              str_ends_with(func->name, "_4core9panicking18panic_bounds_check")                        ||
> > +            str_ends_with(func->name, "_4core9panicking18panic_nounwind_fmt")                        ||
> >              str_ends_with(func->name, "_4core9panicking19assert_failed_inner")                       ||
> >              str_ends_with(func->name, "_4core9panicking30panic_null_pointer_dereference")            ||
> >              str_ends_with(func->name, "_4core9panicking36panic_misaligned_pointer_dereference")      ||
>
> Just having "_4core9panicking" substring is not sufficient?

That prefix just means it is defined in the panicking.rs file, which
also has a few functions that are not noreturn.

Alice

Re: [PATCH 2/2] rust: use `#[used(compiler)]` to fix build and `modpost` with Rust >= 1.89.0

[Alice Ryhl]

On Sat, Jul 12, 2025 at 6:02 PM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> Starting with Rust 1.89.0 (expected 2025-08-07), the Rust compiler fails
> to build the `rusttest` target due to undefined references such as:
>
>     kernel...-cgu.0:(.text....+0x116): undefined reference to
>     `rust_helper_kunit_get_current_test'
>
> Moreover, tooling like `modpost` gets confused:
>
>     WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/nova/nova.o
>     ERROR: modpost: missing MODULE_LICENSE() in drivers/gpu/nova-core/nova_core.o
>
> The reason behind both issues is that the Rust compiler will now [1]
> treat `#[used]` as `#[used(linker)]` instead of `#[used(compiler)]`
> for our targets. This means that the retain section flag (`R`,
> `SHF_GNU_RETAIN`) will be used and that they will be marked as `unique`
> too, with different IDs. In turn, that means we end up with undefined
> references that did not get discarded in `rusttest` and that multiple
> `.modinfo` sections are generated, which confuse tooling like `modpost`
> because they only expect one.
>
> Thus start using `#[used(compiler)]` to keep the previous behavior
> and to be explicit about what we want. Sadly, it is an unstable feature
> (`used_with_arg`) [2] -- we will talk to upstream Rust about it. The good
> news is that it has been available for a long time (Rust >= 1.60) [3].
>
> The changes should also be fine for previous Rust versions, since they
> behave the same way as before [4].
>
> Alternatively, we could use `#[no_mangle]` or `#[export_name = ...]`
> since those still behave like `#[used(compiler)]`, but of course it is
> not really what we want to express, and it requires other changes to
> avoid symbol conflicts.
>
> Cc: Björn Roy Baron <bjorn3_gh@protonmail.com>
> Cc: David Wood <david@davidtw.co>
> Cc: Wesley Wiser <wwiser@gmail.com>
> Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
> Link: https://github.com/rust-lang/rust/pull/140872 [1]
> Link: https://github.com/rust-lang/rust/issues/93798 [2]
> Link: https://github.com/rust-lang/rust/pull/91504 [3]
> Link: https://godbolt.org/z/sxzWTMfzW [4]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

Re: [PATCH 1/2] objtool/rust: add one more `noreturn` Rust function for Rust 1.89.0

[Peter Zijlstra]

On Mon, Jul 14, 2025 at 10:48:33AM +0200, Alice Ryhl wrote:

> > >  tools/objtool/check.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> > > index f23bdda737aa..3257eefc41ed 100644
> > > --- a/tools/objtool/check.c
> > > +++ b/tools/objtool/check.c
> > > @@ -224,6 +224,7 @@ static bool is_rust_noreturn(const struct symbol *func)
> > >              str_ends_with(func->name, "_4core9panicking14panic_explicit")                            ||
> > >              str_ends_with(func->name, "_4core9panicking14panic_nounwind")                            ||
> > >              str_ends_with(func->name, "_4core9panicking18panic_bounds_check")                        ||
> > > +            str_ends_with(func->name, "_4core9panicking18panic_nounwind_fmt")                        ||
> > >              str_ends_with(func->name, "_4core9panicking19assert_failed_inner")                       ||
> > >              str_ends_with(func->name, "_4core9panicking30panic_null_pointer_dereference")            ||
> > >              str_ends_with(func->name, "_4core9panicking36panic_misaligned_pointer_dereference")      ||
> >
> > Just having "_4core9panicking" substring is not sufficient?
> 
> That prefix just means it is defined in the panicking.rs file, which
> also has a few functions that are not noreturn.

Oh well, I figured it was too good to be true anyway. Its just that
there was a lot of that around and I had to ask :-)

Re: [PATCH 0/2] Rust fixes for the upcoming 1.89 release

[Miguel Ojeda]

On Sat, Jul 12, 2025 at 6:01 PM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> A couple fixes for the upcoming 1.89.0 release, currently in beta.
>
> With this, current nightly (1.90) gets also clean.

Applied to `rust-fixes` -- thanks everyone!

I am applying these now so that v6.16 is fine by the time the compiler
releases, giving how their release weeks will likely line up.

(Added Acked-by from Björn to the second patch he gave me after
discussing it in private -- thanks!)

Cheers,
Miguel