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, 72 insertions, 0 deletions

diff --git a/include/soc/tegra/pm.h b/include/soc/tegra/pm.h
new file mode 100644
index 000000000..ce4d0b1bd
--- /dev/null
+++ b/include/soc/tegra/pm.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2014 NVIDIA Corporation
+ */
+
+#ifndef __SOC_TEGRA_PM_H__
+#define __SOC_TEGRA_PM_H__
+
+#include <linux/errno.h>
+
+enum tegra_suspend_mode {
+	TEGRA_SUSPEND_NONE = 0,
+	TEGRA_SUSPEND_LP2, /* CPU voltage off */
+	TEGRA_SUSPEND_LP1, /* CPU voltage off, DRAM self-refresh */
+	TEGRA_SUSPEND_LP0, /* CPU + core voltage off, DRAM self-refresh */
+	TEGRA_MAX_SUSPEND_MODE,
+	TEGRA_SUSPEND_NOT_READY,
+};
+
+#if defined(CONFIG_PM_SLEEP) && defined(CONFIG_ARM) && defined(CONFIG_ARCH_TEGRA)
+enum tegra_suspend_mode
+tegra_pm_validate_suspend_mode(enum tegra_suspend_mode mode);
+
+/* low-level resume entry point */
+void tegra_resume(void);
+
+int tegra30_pm_secondary_cpu_suspend(unsigned long arg);
+void tegra_pm_clear_cpu_in_lp2(void);
+void tegra_pm_set_cpu_in_lp2(void);
+int tegra_pm_enter_lp2(void);
+int tegra_pm_park_secondary_cpu(unsigned long cpu);
+void tegra_pm_init_suspend(void);
+#else
+static inline enum tegra_suspend_mode
+tegra_pm_validate_suspend_mode(enum tegra_suspend_mode mode)
+{
+	return TEGRA_SUSPEND_NONE;
+}
+
+static inline void tegra_resume(void)
+{
+}
+
+static inline int tegra30_pm_secondary_cpu_suspend(unsigned long arg)
+{
+	return -ENOTSUPP;
+}
+
+static inline void tegra_pm_clear_cpu_in_lp2(void)
+{
+}
+
+static inline void tegra_pm_set_cpu_in_lp2(void)
+{
+}
+
+static inline int tegra_pm_enter_lp2(void)
+{
+	return -ENOTSUPP;
+}
+
+static inline int tegra_pm_park_secondary_cpu(unsigned long cpu)
+{
+	return -ENOTSUPP;
+}
+
+static inline void tegra_pm_init_suspend(void)
+{
+}
+#endif /* CONFIG_PM_SLEEP */
+
+#endif /* __SOC_TEGRA_PM_H__ */