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, 34 insertions, 0 deletions

diff --git a/drivers/hte/Kconfig b/drivers/hte/Kconfig
new file mode 100644
index 000000000..f57bad67d
--- /dev/null
+++ b/drivers/hte/Kconfig
@@ -0,0 +1,34 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menuconfig HTE
+	bool "Hardware Timestamping Engine (HTE) Support"
+	help
+	  Hardware Timestamping Engine (HTE) Support.
+
+	  Some devices provide a hardware timestamping engine which can
+	  timestamp certain device lines/signals in realtime. It comes with a
+	  benefit for the applications needing accurate timestamping event with
+	  less jitter. This framework provides a generic interface to such HTE
+	  providers and consumer devices.
+
+	  If unsure, say no.
+
+if HTE
+
+config HTE_TEGRA194
+	tristate "NVIDIA Tegra194 HTE Support"
+	depends on (ARCH_TEGRA || COMPILE_TEST)
+	depends on GPIOLIB
+	help
+	  Enable this option for integrated hardware timestamping engine also
+	  known as generic timestamping engine (GTE) support on NVIDIA Tegra194
+	  and later systems-on-chip. The driver supports 352 LIC IRQs and 39
+	  AON GPIOs lines for timestamping in realtime.
+
+config HTE_TEGRA194_TEST
+        tristate "NVIDIA Tegra194 HTE Test"
+        depends on (HTE_TEGRA194 || COMPILE_TEST)
+        help
+	  The NVIDIA Tegra194 GTE test driver demonstrates how to use HTE
+	  framework to timestamp GPIO and LIC IRQ lines.
+
+endif