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, 43 insertions, 0 deletions

diff --git a/arch/mips/kvm/interrupt.h b/arch/mips/kvm/interrupt.h
new file mode 100644
index 000000000..07bc0160b
--- /dev/null
+++ b/arch/mips/kvm/interrupt.h
@@ -0,0 +1,43 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * KVM/MIPS: Interrupts
+ * Copyright (C) 2012  MIPS Technologies, Inc.  All rights reserved.
+ * Authors: Sanjay Lal <sanjayl@kymasys.com>
+ */
+
+/*
+ * MIPS Exception Priorities, exceptions (including interrupts) are queued up
+ * for the guest in the order specified by their priorities
+ */
+
+#define MIPS_EXC_RESET              0
+#define MIPS_EXC_SRESET             1
+#define MIPS_EXC_DEBUG_ST           2
+#define MIPS_EXC_DEBUG              3
+#define MIPS_EXC_DDB                4
+#define MIPS_EXC_NMI                5
+#define MIPS_EXC_MCHK               6
+#define MIPS_EXC_INT_TIMER          7
+#define MIPS_EXC_INT_IO_1           8
+#define MIPS_EXC_INT_IO_2           9
+#define MIPS_EXC_EXECUTE            10
+#define MIPS_EXC_INT_IPI_1          11
+#define MIPS_EXC_INT_IPI_2          12
+#define MIPS_EXC_MAX                13
+/* XXXSL More to follow */
+
+#define C_TI        (_ULCAST_(1) << 30)
+
+extern u32 *kvm_priority_to_irq;
+u32 kvm_irq_to_priority(u32 irq);
+
+int kvm_mips_pending_timer(struct kvm_vcpu *vcpu);
+
+void kvm_mips_deliver_interrupts(struct kvm_vcpu *vcpu, u32 cause);
+
+#ifdef CONFIG_CPU_LOONGSON64
+extern void kvm_init_loongson_ipi(struct kvm *kvm);
+#endif