Between Rust 1.79 and 1.86, under `CONFIG_RUST_KERNEL_DOCTESTS=y`, `objtool` may report:
rust/doctests_kernel_generated.o: warning: objtool: rust_doctest_kernel_alloc_kbox_rs_13() falls through to next function rust_doctest_kernel_alloc_kvec_rs_0()
(as well as in rust_doctest_kernel_alloc_kvec_rs_0) due to calls to the `noreturn` symbol:
core::option::expect_failed
from code added in commits 779db37373a3 ("rust: alloc: kvec: implement AsPageIter for VVec") and 671618432f46 ("rust: alloc: kbox: implement AsPageIter for VBox").
Thus add the mangled one to the list so that `objtool` knows it is actually `noreturn`.
This can be reproduced as well in other versions by tweaking the code, such as the latest stable Rust (1.90.0).
Stable does not have code that triggers this, but it could have it in the future. Downstream forks could too. Thus tag it for backport.
See commit 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions") for more details.
Cc: stable@vger.kernel.org # Needed in 6.12.y and later. 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 a5770570b106..3c7ab910b189 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -217,6 +217,7 @@ static bool is_rust_noreturn(const struct symbol *func) * these come from the Rust standard library). */ return str_ends_with(func->name, "_4core5sliceSp15copy_from_slice17len_mismatch_fail") || + str_ends_with(func->name, "_4core6option13expect_failed") || str_ends_with(func->name, "_4core6option13unwrap_failed") || str_ends_with(func->name, "_4core6result13unwrap_failed") || str_ends_with(func->name, "_4core9panicking5panic") ||
base-commit: 211ddde0823f1442e4ad052a2f30f050145ccada
On Mon, Oct 20, 2025 at 04:07:14AM +0200, Miguel Ojeda wrote:
Between Rust 1.79 and 1.86, under `CONFIG_RUST_KERNEL_DOCTESTS=y`, `objtool` may report:
rust/doctests_kernel_generated.o: warning: objtool: rust_doctest_kernel_alloc_kbox_rs_13() falls through to next function rust_doctest_kernel_alloc_kvec_rs_0()(as well as in rust_doctest_kernel_alloc_kvec_rs_0) due to calls to the `noreturn` symbol:
core::option::expect_failedfrom code added in commits 779db37373a3 ("rust: alloc: kvec: implement AsPageIter for VVec") and 671618432f46 ("rust: alloc: kbox: implement AsPageIter for VBox").
Thus add the mangled one to the list so that `objtool` knows it is actually `noreturn`.
This can be reproduced as well in other versions by tweaking the code, such as the latest stable Rust (1.90.0).
Stable does not have code that triggers this, but it could have it in the future. Downstream forks could too. Thus tag it for backport.
See commit 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions") for more details.
Cc: stable@vger.kernel.org # Needed in 6.12.y and later. Cc: Josh Poimboeuf jpoimboe@kernel.org Cc: Peter Zijlstra peterz@infradead.org Signed-off-by: Miguel Ojeda ojeda@kernel.org
Reviewed-by: Alice Ryhl aliceryhl@google.com
On Mon, Oct 20, 2025 at 04:07:14AM +0200, Miguel Ojeda wrote:
Between Rust 1.79 and 1.86, under `CONFIG_RUST_KERNEL_DOCTESTS=y`, `objtool` may report:
rust/doctests_kernel_generated.o: warning: objtool: rust_doctest_kernel_alloc_kbox_rs_13() falls through to next function rust_doctest_kernel_alloc_kvec_rs_0()(as well as in rust_doctest_kernel_alloc_kvec_rs_0) due to calls to the `noreturn` symbol:
core::option::expect_failedfrom code added in commits 779db37373a3 ("rust: alloc: kvec: implement AsPageIter for VVec") and 671618432f46 ("rust: alloc: kbox: implement AsPageIter for VBox").
Thus add the mangled one to the list so that `objtool` knows it is actually `noreturn`.
This can be reproduced as well in other versions by tweaking the code, such as the latest stable Rust (1.90.0).
Stable does not have code that triggers this, but it could have it in the future. Downstream forks could too. Thus tag it for backport.
See commit 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions") for more details.
Cc: stable@vger.kernel.org # Needed in 6.12.y and later. 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 a5770570b106..3c7ab910b189 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -217,6 +217,7 @@ static bool is_rust_noreturn(const struct symbol *func) * these come from the Rust standard library). */ return str_ends_with(func->name, "_4core5sliceSp15copy_from_slice17len_mismatch_fail") ||
str_ends_with(func->name, "_4core6option13expect_failed") || str_ends_with(func->name, "_4core6option13unwrap_failed") || str_ends_with(func->name, "_4core6result13unwrap_failed") || str_ends_with(func->name, "_4core9panicking5panic") ||
I'll go stick it in tip/objtool/core; but I gotta ask, where are we with the toolchain support for noreturn?
On Tue, Oct 21, 2025 at 7:19 PM Peter Zijlstra peterz@infradead.org wrote:
I'll go stick it in tip/objtool/core; but I gotta ask, where are we with the toolchain support for noreturn?
Thanks Peter!
We discussed it with upstream Rust, and they understood the need, so we may get something like `--emit=noreturn` or similar, but it is still open (and not too high in the priority list since we can survive with this for now and we have other things that we really need them to get stabilized etc. But if you feel it should be prioritized more, please let me know).
I have the status under "Export (somehow) a list of all noreturn symbols." at:
https://github.com/Rust-for-Linux/linux/issues/355
In particular, Gary proposed an alternative during those discussions:
"Gary proposed reading DWARF instead and wrote a quick Rust script for it via object and gimli, though DWARF would need to be available or generated on the fly just for that (and we cannot commit a fixed list since the kernel config may change and we support several Rust versions and so on): https://gist.github.com/nbdd0121/449692570622c2f46a29ad9f47c3379a."
Cheers, Miguel
On Tue, Oct 21, 2025 at 07:25:11PM +0200, Miguel Ojeda wrote:
On Tue, Oct 21, 2025 at 7:19 PM Peter Zijlstra peterz@infradead.org wrote:
I'll go stick it in tip/objtool/core; but I gotta ask, where are we with the toolchain support for noreturn?
Thanks Peter!
We discussed it with upstream Rust, and they understood the need, so we may get something like `--emit=noreturn` or similar, but it is still open (and not too high in the priority list since we can survive with this for now and we have other things that we really need them to get stabilized etc. But if you feel it should be prioritized more, please let me know).
Nah, as long as its not forgotten I suppose it'll show up at some point.
I would place including C headers in Rust at a *MUCH* higher priority than this. This bindgen nonsense is a giant pain in the arse.
I have the status under "Export (somehow) a list of all noreturn symbols." at:
https://github.com/Rust-for-Linux/linux/issues/355In particular, Gary proposed an alternative during those discussions:
"Gary proposed reading DWARF instead and wrote a quick Rust scriptfor it via object and gimli, though DWARF would need to be available or generated on the fly just for that (and we cannot commit a fixed list since the kernel config may change and we support several Rust versions and so on): https://gist.github.com/nbdd0121/449692570622c2f46a29ad9f47c3379a."
Right, the problem with DWARF is that you need to have DWARF and debug builds are *SLOW* :/ But perhaps rust compile times are such that that isn't noticable?
The following commit has been merged into the objtool/urgent branch of tip:
Commit-ID: dbdf2a7feb422f9bacfd12774e624cf26f503eb0 Gitweb: https://git.kernel.org/tip/dbdf2a7feb422f9bacfd12774e624cf26f503eb0 Author: Miguel Ojeda ojeda@kernel.org AuthorDate: Mon, 20 Oct 2025 04:07:14 +02:00 Committer: Peter Zijlstra peterz@infradead.org CommitterDate: Wed, 22 Oct 2025 15:21:54 +02:00
objtool/rust: add one more `noreturn` Rust function
Between Rust 1.79 and 1.86, under `CONFIG_RUST_KERNEL_DOCTESTS=y`, `objtool` may report:
rust/doctests_kernel_generated.o: warning: objtool: rust_doctest_kernel_alloc_kbox_rs_13() falls through to next function rust_doctest_kernel_alloc_kvec_rs_0()
(as well as in rust_doctest_kernel_alloc_kvec_rs_0) due to calls to the `noreturn` symbol:
core::option::expect_failed
from code added in commits 779db37373a3 ("rust: alloc: kvec: implement AsPageIter for VVec") and 671618432f46 ("rust: alloc: kbox: implement AsPageIter for VBox").
Thus add the mangled one to the list so that `objtool` knows it is actually `noreturn`.
This can be reproduced as well in other versions by tweaking the code, such as the latest stable Rust (1.90.0).
Stable does not have code that triggers this, but it could have it in the future. Downstream forks could too. Thus tag it for backport.
See commit 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions") for more details.
Signed-off-by: Miguel Ojeda ojeda@kernel.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Alice Ryhl aliceryhl@google.com Cc: stable@vger.kernel.org # Needed in 6.12.y and later. Link: https://patch.msgid.link/20251020020714.2511718-1-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 a577057..3c7ab91 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -217,6 +217,7 @@ static bool is_rust_noreturn(const struct symbol *func) * these come from the Rust standard library). */ return str_ends_with(func->name, "_4core5sliceSp15copy_from_slice17len_mismatch_fail") || + str_ends_with(func->name, "_4core6option13expect_failed") || str_ends_with(func->name, "_4core6option13unwrap_failed") || str_ends_with(func->name, "_4core6result13unwrap_failed") || str_ends_with(func->name, "_4core9panicking5panic") ||
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