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, 23 insertions, 0 deletions

diff --git a/Documentation/crypto/api-akcipher.rst b/Documentation/crypto/api-akcipher.rst
new file mode 100644
index 000000000..a31f5aef7
--- /dev/null
+++ b/Documentation/crypto/api-akcipher.rst
@@ -0,0 +1,23 @@
+Asymmetric Cipher
+=================
+
+Asymmetric Cipher Algorithm Definitions
+---------------------------------------
+
+.. kernel-doc:: include/crypto/akcipher.h
+   :functions: akcipher_alg akcipher_request
+
+Asymmetric Cipher API
+---------------------
+
+.. kernel-doc:: include/crypto/akcipher.h
+   :doc: Generic Public Key Cipher API
+
+.. kernel-doc:: include/crypto/akcipher.h
+   :functions: crypto_alloc_akcipher crypto_free_akcipher crypto_akcipher_set_pub_key crypto_akcipher_set_priv_key crypto_akcipher_maxsize crypto_akcipher_encrypt crypto_akcipher_decrypt
+
+Asymmetric Cipher Request Handle
+--------------------------------
+
+.. kernel-doc:: include/crypto/akcipher.h
+   :functions: akcipher_request_alloc akcipher_request_free akcipher_request_set_callback akcipher_request_set_crypt