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, 89 insertions, 0 deletions

diff --git a/drivers/ps3/vuart.h b/drivers/ps3/vuart.h
new file mode 100644
index 000000000..64d34efef
--- /dev/null
+++ b/drivers/ps3/vuart.h
@@ -0,0 +1,89 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  PS3 virtual uart
+ *
+ *  Copyright (C) 2006 Sony Computer Entertainment Inc.
+ *  Copyright 2006 Sony Corp.
+ */
+
+#if !defined(_PS3_VUART_H)
+#define _PS3_VUART_H
+
+#include <asm/ps3.h>
+
+struct ps3_vuart_stats {
+	unsigned long bytes_written;
+	unsigned long bytes_read;
+	unsigned long tx_interrupts;
+	unsigned long rx_interrupts;
+	unsigned long disconnect_interrupts;
+};
+
+struct ps3_vuart_work {
+	struct work_struct work;
+	unsigned long trigger;
+	struct ps3_system_bus_device *dev; /* to convert work to device */
+};
+
+/**
+ * struct ps3_vuart_port_driver - a driver for a device on a vuart port
+ */
+
+struct ps3_vuart_port_driver {
+	struct ps3_system_bus_driver core;
+	int (*probe)(struct ps3_system_bus_device *);
+	int (*remove)(struct ps3_system_bus_device *);
+	void (*shutdown)(struct ps3_system_bus_device *);
+	void (*work)(struct ps3_system_bus_device *);
+	/* int (*tx_event)(struct ps3_system_bus_device *dev); */
+	/* int (*rx_event)(struct ps3_system_bus_device *dev); */
+	/* int (*disconnect_event)(struct ps3_system_bus_device *dev); */
+	/* int (*suspend)(struct ps3_system_bus_device *, pm_message_t); */
+	/* int (*resume)(struct ps3_system_bus_device *); */
+};
+
+int ps3_vuart_port_driver_register(struct ps3_vuart_port_driver *drv);
+void ps3_vuart_port_driver_unregister(struct ps3_vuart_port_driver *drv);
+
+static inline struct ps3_vuart_port_driver *
+	ps3_system_bus_dev_to_vuart_drv(struct ps3_system_bus_device *_dev)
+{
+	struct ps3_system_bus_driver *sbd =
+		ps3_system_bus_dev_to_system_bus_drv(_dev);
+	BUG_ON(!sbd);
+	return container_of(sbd, struct ps3_vuart_port_driver, core);
+}
+static inline struct ps3_system_bus_device *ps3_vuart_work_to_system_bus_dev(
+	struct work_struct *_work)
+{
+	struct ps3_vuart_work *vw = container_of(_work, struct ps3_vuart_work,
+		work);
+	return vw->dev;
+}
+
+int ps3_vuart_write(struct ps3_system_bus_device *dev, const void *buf,
+	unsigned int bytes);
+int ps3_vuart_read(struct ps3_system_bus_device *dev, void *buf,
+	unsigned int bytes);
+int ps3_vuart_read_async(struct ps3_system_bus_device *dev, unsigned int bytes);
+void ps3_vuart_cancel_async(struct ps3_system_bus_device *dev);
+void ps3_vuart_clear_rx_bytes(struct ps3_system_bus_device *dev,
+	unsigned int bytes);
+
+struct vuart_triggers {
+	unsigned long rx;
+	unsigned long tx;
+};
+
+int ps3_vuart_get_triggers(struct ps3_system_bus_device *dev,
+	struct vuart_triggers *trig);
+int ps3_vuart_set_triggers(struct ps3_system_bus_device *dev, unsigned int tx,
+	unsigned int rx);
+int ps3_vuart_enable_interrupt_tx(struct ps3_system_bus_device *dev);
+int ps3_vuart_disable_interrupt_tx(struct ps3_system_bus_device *dev);
+int ps3_vuart_enable_interrupt_rx(struct ps3_system_bus_device *dev);
+int ps3_vuart_disable_interrupt_rx(struct ps3_system_bus_device *dev);
+int ps3_vuart_enable_interrupt_disconnect(struct ps3_system_bus_device *dev);
+int ps3_vuart_disable_interrupt_disconnect(struct ps3_system_bus_device *dev);
+
+#endif