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, 36 insertions, 0 deletions

diff --git a/drivers/accessibility/Kconfig b/drivers/accessibility/Kconfig
new file mode 100644
index 000000000..6b2f79d1f
--- /dev/null
+++ b/drivers/accessibility/Kconfig
@@ -0,0 +1,36 @@
+# SPDX-License-Identifier: GPL-2.0
+menuconfig ACCESSIBILITY
+	bool "Accessibility support"
+	help
+	  Accessibility handles all special kinds of hardware devices or
+	  software adapters which help people with disabilities (e.g.
+	  blindness) to use computers.
+
+	  That includes braille devices, speech synthesis, keyboard
+	  remapping, etc.
+
+	  Say Y here to get to see options for accessibility.
+	  This option alone does not add any kernel code.
+
+	  If you say N, all options in this submenu will be skipped and disabled.
+
+	  If unsure, say N.
+
+if ACCESSIBILITY
+config A11Y_BRAILLE_CONSOLE
+	bool "Console on braille device"
+	depends on VT
+	depends on SERIAL_CORE_CONSOLE
+	help
+	  Enables console output on a braille device connected to a 8250
+	  serial port. For now only the VisioBraille device is supported.
+
+	  To actually enable it, you need to pass option
+	  console=brl,ttyS0
+	  to the kernel. Options are the same as for serial console.
+
+	  If unsure, say N.
+
+source "drivers/accessibility/speakup/Kconfig"
+
+endif # ACCESSIBILITY