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, 47 insertions, 0 deletions

diff --git a/include/soc/tegra/tegra-cbb.h b/include/soc/tegra/tegra-cbb.h
new file mode 100644
index 000000000..e864c2ebe
--- /dev/null
+++ b/include/soc/tegra/tegra-cbb.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2021-2022, NVIDIA CORPORATION. All rights reserved
+ */
+
+#ifndef TEGRA_CBB_H
+#define TEGRA_CBB_H
+
+#include <linux/list.h>
+
+struct tegra_cbb_error {
+	const char *code;
+	const char *source;
+	const char *desc;
+};
+
+struct tegra_cbb {
+	struct device *dev;
+	const struct tegra_cbb_ops *ops;
+	struct list_head node;
+};
+
+struct tegra_cbb_ops {
+	int (*debugfs_show)(struct tegra_cbb *cbb, struct seq_file *s, void *v);
+	int (*interrupt_enable)(struct tegra_cbb *cbb);
+	void (*error_enable)(struct tegra_cbb *cbb);
+	void (*fault_enable)(struct tegra_cbb *cbb);
+	void (*stall_enable)(struct tegra_cbb *cbb);
+	void (*error_clear)(struct tegra_cbb *cbb);
+	u32 (*get_status)(struct tegra_cbb *cbb);
+};
+
+int tegra_cbb_get_irq(struct platform_device *pdev, unsigned int *nonsec_irq,
+		      unsigned int *sec_irq);
+__printf(2, 3)
+void tegra_cbb_print_err(struct seq_file *file, const char *fmt, ...);
+
+void tegra_cbb_print_cache(struct seq_file *file, u32 cache);
+void tegra_cbb_print_prot(struct seq_file *file, u32 prot);
+int tegra_cbb_register(struct tegra_cbb *cbb);
+
+void tegra_cbb_fault_enable(struct tegra_cbb *cbb);
+void tegra_cbb_stall_enable(struct tegra_cbb *cbb);
+void tegra_cbb_error_clear(struct tegra_cbb *cbb);
+u32 tegra_cbb_get_status(struct tegra_cbb *cbb);
+
+#endif /* TEGRA_CBB_H */