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, 60 insertions, 0 deletions

diff --git a/arch/powerpc/sysdev/mpic.h b/arch/powerpc/sysdev/mpic.h
new file mode 100644
index 000000000..bb460ff57
--- /dev/null
+++ b/arch/powerpc/sysdev/mpic.h
@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _POWERPC_SYSDEV_MPIC_H
+#define _POWERPC_SYSDEV_MPIC_H
+
+/*
+ * Copyright 2006-2007, Michael Ellerman, IBM Corporation.
+ */
+
+#ifdef CONFIG_PCI_MSI
+extern void mpic_msi_reserve_hwirq(struct mpic *mpic, irq_hw_number_t hwirq);
+int __init mpic_msi_init_allocator(struct mpic *mpic);
+int __init mpic_u3msi_init(struct mpic *mpic);
+#else
+static inline void mpic_msi_reserve_hwirq(struct mpic *mpic,
+					  irq_hw_number_t hwirq)
+{
+	return;
+}
+
+static inline int mpic_u3msi_init(struct mpic *mpic)
+{
+	return -1;
+}
+#endif
+
+#if defined(CONFIG_PCI_MSI) && defined(CONFIG_PPC_PASEMI)
+int __init mpic_pasemi_msi_init(struct mpic *mpic);
+#else
+static inline int mpic_pasemi_msi_init(struct mpic *mpic) { return -1; }
+#endif
+
+extern int mpic_set_irq_type(struct irq_data *d, unsigned int flow_type);
+extern void mpic_set_vector(unsigned int virq, unsigned int vector);
+extern int mpic_set_affinity(struct irq_data *d,
+			     const struct cpumask *cpumask, bool force);
+extern void mpic_reset_core(int cpu);
+
+#ifdef CONFIG_FSL_SOC
+extern int mpic_map_error_int(struct mpic *mpic, unsigned int virq, irq_hw_number_t  hw);
+void __init mpic_err_int_init(struct mpic *mpic, irq_hw_number_t irqnum);
+int __init mpic_setup_error_int(struct mpic *mpic, int intvec);
+#else
+static inline int mpic_map_error_int(struct mpic *mpic, unsigned int virq, irq_hw_number_t  hw)
+{
+	return 0;
+}
+
+
+static inline void mpic_err_int_init(struct mpic *mpic, irq_hw_number_t irqnum)
+{
+	return;
+}
+
+static inline int mpic_setup_error_int(struct mpic *mpic, int intvec)
+{
+	return -1;
+}
+#endif
+
+#endif /* _POWERPC_SYSDEV_MPIC_H */