kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/Documentation/crypto/api-digest.rst b/Documentation/crypto/api-digest.rst
new file mode 100644
index 000000000..02a2bcc26
--- /dev/null
+++ b/Documentation/crypto/api-digest.rst
@@ -0,0 +1,38 @@
+Message Digest
+==============
+
+Message Digest Algorithm Definitions
+------------------------------------
+
+.. kernel-doc:: include/crypto/hash.h
+   :doc: Message Digest Algorithm Definitions
+
+.. kernel-doc:: include/crypto/hash.h
+   :functions: hash_alg_common ahash_alg shash_alg
+
+Asynchronous Message Digest API
+-------------------------------
+
+.. kernel-doc:: include/crypto/hash.h
+   :doc: Asynchronous Message Digest API
+
+.. kernel-doc:: include/crypto/hash.h
+   :functions: crypto_alloc_ahash crypto_free_ahash crypto_ahash_init crypto_ahash_digestsize crypto_ahash_reqtfm crypto_ahash_reqsize crypto_ahash_statesize crypto_ahash_setkey crypto_ahash_finup crypto_ahash_final crypto_ahash_digest crypto_ahash_export crypto_ahash_import
+
+Asynchronous Hash Request Handle
+--------------------------------
+
+.. kernel-doc:: include/crypto/hash.h
+   :doc: Asynchronous Hash Request Handle
+
+.. kernel-doc:: include/crypto/hash.h
+   :functions: ahash_request_set_tfm ahash_request_alloc ahash_request_free ahash_request_set_callback ahash_request_set_crypt
+
+Synchronous Message Digest API
+------------------------------
+
+.. kernel-doc:: include/crypto/hash.h
+   :doc: Synchronous Message Digest API
+
+.. kernel-doc:: include/crypto/hash.h
+   :functions: crypto_alloc_shash crypto_free_shash crypto_shash_blocksize crypto_shash_digestsize crypto_shash_descsize crypto_shash_setkey crypto_shash_digest crypto_shash_export crypto_shash_import crypto_shash_init crypto_shash_update crypto_shash_final crypto_shash_finup