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, 88 insertions, 0 deletions

diff --git a/include/sound/i2c.h b/include/sound/i2c.h
new file mode 100644
index 000000000..6f0162ae9
--- /dev/null
+++ b/include/sound/i2c.h
@@ -0,0 +1,88 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __SOUND_I2C_H
+#define __SOUND_I2C_H
+
+/*
+ */
+
+#define SND_I2C_DEVICE_ADDRTEN	(1<<0)	/* 10-bit I2C address */
+
+struct snd_i2c_device {
+	struct list_head list;
+	struct snd_i2c_bus *bus;	/* I2C bus */
+	char name[32];		/* some useful device name */
+	unsigned short flags;	/* device flags */
+	unsigned short addr;	/* device address (might be 10-bit) */
+	unsigned long private_value;
+	void *private_data;
+	void (*private_free)(struct snd_i2c_device *device);
+};
+
+#define snd_i2c_device(n) list_entry(n, struct snd_i2c_device, list)
+
+struct snd_i2c_bit_ops {
+	void (*start)(struct snd_i2c_bus *bus);	/* transfer start */
+	void (*stop)(struct snd_i2c_bus *bus);	/* transfer stop */
+	void (*direction)(struct snd_i2c_bus *bus, int clock, int data);  /* set line direction (0 = write, 1 = read) */
+	void (*setlines)(struct snd_i2c_bus *bus, int clock, int data);
+	int (*getclock)(struct snd_i2c_bus *bus);
+	int (*getdata)(struct snd_i2c_bus *bus, int ack);
+};
+
+struct snd_i2c_ops {
+	int (*sendbytes)(struct snd_i2c_device *device, unsigned char *bytes, int count);
+	int (*readbytes)(struct snd_i2c_device *device, unsigned char *bytes, int count);
+	int (*probeaddr)(struct snd_i2c_bus *bus, unsigned short addr);
+};
+
+struct snd_i2c_bus {
+	struct snd_card *card;	/* card which I2C belongs to */
+	char name[32];		/* some useful label */
+
+	struct mutex lock_mutex;
+
+	struct snd_i2c_bus *master;	/* master bus when SCK/SCL is shared */
+	struct list_head buses;	/* master: slave buses sharing SCK/SCL, slave: link list */
+
+	struct list_head devices; /* attached devices to this bus */
+
+	union {
+		struct snd_i2c_bit_ops *bit;
+		void *ops;
+	} hw_ops;		/* lowlevel operations */
+	const struct snd_i2c_ops *ops;	/* midlevel operations */
+
+	unsigned long private_value;
+	void *private_data;
+	void (*private_free)(struct snd_i2c_bus *bus);
+};
+
+#define snd_i2c_slave_bus(n) list_entry(n, struct snd_i2c_bus, buses)
+
+int snd_i2c_bus_create(struct snd_card *card, const char *name,
+		       struct snd_i2c_bus *master, struct snd_i2c_bus **ri2c);
+int snd_i2c_device_create(struct snd_i2c_bus *bus, const char *name,
+			  unsigned char addr, struct snd_i2c_device **rdevice);
+int snd_i2c_device_free(struct snd_i2c_device *device);
+
+static inline void snd_i2c_lock(struct snd_i2c_bus *bus)
+{
+	if (bus->master)
+		mutex_lock(&bus->master->lock_mutex);
+	else
+		mutex_lock(&bus->lock_mutex);
+}
+
+static inline void snd_i2c_unlock(struct snd_i2c_bus *bus)
+{
+	if (bus->master)
+		mutex_unlock(&bus->master->lock_mutex);
+	else
+		mutex_unlock(&bus->lock_mutex);
+}
+
+int snd_i2c_sendbytes(struct snd_i2c_device *device, unsigned char *bytes, int count);
+int snd_i2c_readbytes(struct snd_i2c_device *device, unsigned char *bytes, int count);
+int snd_i2c_probeaddr(struct snd_i2c_bus *bus, unsigned short addr);
+
+#endif /* __SOUND_I2C_H */