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/i3c/Kconfig b/drivers/i3c/Kconfig
new file mode 100644
index 000000000..626c54b38
--- /dev/null
+++ b/drivers/i3c/Kconfig
@@ -0,0 +1,36 @@
+# SPDX-License-Identifier: GPL-2.0
+
+menuconfig I3C
+	tristate "I3C support"
+	select I2C
+	help
+	  I3C is a serial protocol standardized by the MIPI alliance.
+
+	  It's supposed to be backward compatible with I2C while providing
+	  support for high speed transfers and native interrupt support
+	  without the need for extra pins.
+
+	  The I3C protocol also standardizes the slave device types and is
+	  mainly designed to communicate with sensors.
+
+	  If you want I3C support, you should say Y here and also to the
+	  specific driver for your bus adapter(s) below.
+
+	  This I3C support can also be built as a module.  If so, the module
+	  will be called i3c.
+
+if I3C
+source "drivers/i3c/master/Kconfig"
+endif # I3C
+
+config I3C_OR_I2C
+	tristate
+	default m if I3C=m
+	default I2C
+	help
+	  Device drivers using module_i3c_i2c_driver() can use either
+	  i2c or i3c hosts, but cannot be built-in for the kernel when
+	  CONFIG_I3C=m.
+
+	  Add 'depends on I2C_OR_I3C' in Kconfig for those drivers to
+	  get the correct dependencies.