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, 28 insertions, 0 deletions

diff --git a/fs/befs/Kconfig b/fs/befs/Kconfig
new file mode 100644
index 000000000..5fcfc4024
--- /dev/null
+++ b/fs/befs/Kconfig
@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config BEFS_FS
+	tristate "BeOS file system (BeFS) support (read only)"
+	depends on BLOCK
+	select BUFFER_HEAD
+	select NLS
+	help
+	  The BeOS File System (BeFS) is the native file system of Be, Inc's
+	  BeOS. Notable features include support for arbitrary attributes
+	  on files and directories, and database-like indices on selected
+	  attributes. (Also note that this driver doesn't make those features
+	  available at this time). It is a 64 bit filesystem, so it supports
+	  extremely large volumes and files.
+
+	  If you use this filesystem, you should also say Y to at least one
+	  of the NLS (native language support) options below.
+
+	  If you don't know what this is about, say N.
+
+	  To compile this as a module, choose M here: the module will be
+	  called befs.
+
+config BEFS_DEBUG
+	bool "Debug BeFS"
+	depends on BEFS_FS
+	help
+	  If you say Y here, you can use the 'debug' mount option to enable
+	  debugging output from the driver.