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, 75 insertions, 0 deletions

diff --git a/drivers/i3c/internals.h b/drivers/i3c/internals.h
new file mode 100644
index 000000000..0f1f3f766
--- /dev/null
+++ b/drivers/i3c/internals.h
@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2018 Cadence Design Systems Inc.
+ *
+ * Author: Boris Brezillon <boris.brezillon@bootlin.com>
+ */
+
+#ifndef I3C_INTERNALS_H
+#define I3C_INTERNALS_H
+
+#include <linux/i3c/master.h>
+#include <linux/io.h>
+
+int __must_check i3c_bus_rpm_get(struct i3c_bus *bus);
+void i3c_bus_rpm_put(struct i3c_bus *bus);
+bool i3c_bus_rpm_ibi_allowed(struct i3c_bus *bus);
+
+void i3c_bus_normaluse_lock(struct i3c_bus *bus);
+void i3c_bus_normaluse_unlock(struct i3c_bus *bus);
+
+int i3c_dev_setdasa_locked(struct i3c_dev_desc *dev);
+int i3c_dev_do_xfers_locked(struct i3c_dev_desc *dev,
+			    struct i3c_xfer *xfers,
+			    int nxfers, enum i3c_xfer_mode mode);
+int i3c_dev_disable_ibi_locked(struct i3c_dev_desc *dev);
+int i3c_dev_enable_ibi_locked(struct i3c_dev_desc *dev);
+int i3c_dev_request_ibi_locked(struct i3c_dev_desc *dev,
+			       const struct i3c_ibi_setup *req);
+void i3c_dev_free_ibi_locked(struct i3c_dev_desc *dev);
+
+/**
+ * i3c_writel_fifo - Write data buffer to 32bit FIFO
+ * @addr: FIFO Address to write to
+ * @buf: Pointer to the data bytes to write
+ * @nbytes: Number of bytes to write
+ */
+static inline void i3c_writel_fifo(void __iomem *addr, const void *buf,
+				   int nbytes)
+{
+	writesl(addr, buf, nbytes / 4);
+	if (nbytes & 3) {
+		u32 tmp = 0;
+
+		memcpy(&tmp, buf + (nbytes & ~3), nbytes & 3);
+		/*
+		 * writesl() instead of writel() to keep FIFO
+		 * byteorder on big-endian targets
+		 */
+		writesl(addr, &tmp, 1);
+	}
+}
+
+/**
+ * i3c_readl_fifo - Read data buffer from 32bit FIFO
+ * @addr: FIFO Address to read from
+ * @buf: Pointer to the buffer to store read bytes
+ * @nbytes: Number of bytes to read
+ */
+static inline void i3c_readl_fifo(const void __iomem *addr, void *buf,
+				  int nbytes)
+{
+	readsl(addr, buf, nbytes / 4);
+	if (nbytes & 3) {
+		u32 tmp;
+
+		/*
+		 * readsl() instead of readl() to keep FIFO
+		 * byteorder on big-endian targets
+		 */
+		readsl(addr, &tmp, 1);
+		memcpy(buf + (nbytes & ~3), &tmp, nbytes & 3);
+	}
+}
+
+#endif /* I3C_INTERNAL_H */