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, 81 insertions, 0 deletions

diff --git a/include/rv/automata.h b/include/rv/automata.h
new file mode 100644
index 000000000..4a4eb40cf
--- /dev/null
+++ b/include/rv/automata.h
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2019-2022 Red Hat, Inc. Daniel Bristot de Oliveira  <bristot@kernel.org>
+ *
+ * Deterministic automata helper functions, to be used with the automata
+ * models in C generated by the dot2k tool.
+ */
+
+#ifndef _RV_AUTOMATA_H
+#define _RV_AUTOMATA_H
+
+#ifndef MONITOR_NAME
+#error "MONITOR_NAME macro is not defined. Did you include $(MODEL_NAME).h generated by rvgen?"
+#endif
+
+#define RV_AUTOMATON_NAME CONCATENATE(automaton_, MONITOR_NAME)
+#define EVENT_MAX CONCATENATE(event_max_, MONITOR_NAME)
+#define STATE_MAX CONCATENATE(state_max_, MONITOR_NAME)
+#define events CONCATENATE(events_, MONITOR_NAME)
+#define states CONCATENATE(states_, MONITOR_NAME)
+
+/*
+ * model_get_state_name - return the (string) name of the given state
+ */
+static char *model_get_state_name(enum states state)
+{
+	if ((state < 0) || (state >= STATE_MAX))
+		return "INVALID";
+
+	return RV_AUTOMATON_NAME.state_names[state];
+}
+
+/*
+ * model_get_event_name - return the (string) name of the given event
+ */
+static char *model_get_event_name(enum events event)
+{
+	if ((event < 0) || (event >= EVENT_MAX))
+		return "INVALID";
+
+	return RV_AUTOMATON_NAME.event_names[event];
+}
+
+/*
+ * model_get_initial_state - return the automaton's initial state
+ */
+static inline enum states model_get_initial_state(void)
+{
+	return RV_AUTOMATON_NAME.initial_state;
+}
+
+/*
+ * model_get_next_state - process an automaton event occurrence
+ *
+ * Given the current state (curr_state) and the event (event), returns
+ * the next state, or INVALID_STATE in case of error.
+ */
+static inline enum states model_get_next_state(enum states curr_state,
+					enum events event)
+{
+	if ((curr_state < 0) || (curr_state >= STATE_MAX))
+		return INVALID_STATE;
+
+	if ((event < 0) || (event >= EVENT_MAX))
+		return INVALID_STATE;
+
+	return RV_AUTOMATON_NAME.function[curr_state][event];
+}
+
+/*
+ * model_is_final_state - check if the given state is a final state
+ */
+static inline bool model_is_final_state(enum states state)
+{
+	if ((state < 0) || (state >= STATE_MAX))
+		return 0;
+
+	return RV_AUTOMATON_NAME.final_states[state];
+}
+
+#endif