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, 108 insertions, 0 deletions

diff --git a/drivers/usb/chipidea/ulpi.c b/drivers/usb/chipidea/ulpi.c
new file mode 100644
index 000000000..dfec07e8a
--- /dev/null
+++ b/drivers/usb/chipidea/ulpi.c
@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2016 Linaro Ltd.
+ */
+
+#include <linux/device.h>
+#include <linux/usb/chipidea.h>
+#include <linux/ulpi/interface.h>
+
+#include "ci.h"
+
+#define ULPI_WAKEUP		BIT(31)
+#define ULPI_RUN		BIT(30)
+#define ULPI_WRITE		BIT(29)
+#define ULPI_SYNC_STATE		BIT(27)
+#define ULPI_ADDR(n)		((n) << 16)
+#define ULPI_DATA(n)		(n)
+
+static int ci_ulpi_wait(struct ci_hdrc *ci, u32 mask)
+{
+	unsigned long usec = 10000;
+
+	while (usec--) {
+		if (!hw_read(ci, OP_ULPI_VIEWPORT, mask))
+			return 0;
+
+		udelay(1);
+	}
+
+	return -ETIMEDOUT;
+}
+
+static int ci_ulpi_read(struct device *dev, u8 addr)
+{
+	struct ci_hdrc *ci = dev_get_drvdata(dev);
+	int ret;
+
+	hw_write(ci, OP_ULPI_VIEWPORT, 0xffffffff, ULPI_WRITE | ULPI_WAKEUP);
+	ret = ci_ulpi_wait(ci, ULPI_WAKEUP);
+	if (ret)
+		return ret;
+
+	hw_write(ci, OP_ULPI_VIEWPORT, 0xffffffff, ULPI_RUN | ULPI_ADDR(addr));
+	ret = ci_ulpi_wait(ci, ULPI_RUN);
+	if (ret)
+		return ret;
+
+	return hw_read(ci, OP_ULPI_VIEWPORT, GENMASK(15, 8)) >> 8;
+}
+
+static int ci_ulpi_write(struct device *dev, u8 addr, u8 val)
+{
+	struct ci_hdrc *ci = dev_get_drvdata(dev);
+	int ret;
+
+	hw_write(ci, OP_ULPI_VIEWPORT, 0xffffffff, ULPI_WRITE | ULPI_WAKEUP);
+	ret = ci_ulpi_wait(ci, ULPI_WAKEUP);
+	if (ret)
+		return ret;
+
+	hw_write(ci, OP_ULPI_VIEWPORT, 0xffffffff,
+		 ULPI_RUN | ULPI_WRITE | ULPI_ADDR(addr) | val);
+	return ci_ulpi_wait(ci, ULPI_RUN);
+}
+
+int ci_ulpi_init(struct ci_hdrc *ci)
+{
+	if (ci->platdata->phy_mode != USBPHY_INTERFACE_MODE_ULPI)
+		return 0;
+
+	/*
+	 * Set PORTSC correctly so we can read/write ULPI registers for
+	 * identification purposes
+	 */
+	hw_phymode_configure(ci);
+
+	ci->ulpi_ops.read = ci_ulpi_read;
+	ci->ulpi_ops.write = ci_ulpi_write;
+	ci->ulpi = ulpi_register_interface(ci->dev, &ci->ulpi_ops);
+	if (IS_ERR(ci->ulpi))
+		dev_err(ci->dev, "failed to register ULPI interface");
+
+	return PTR_ERR_OR_ZERO(ci->ulpi);
+}
+
+void ci_ulpi_exit(struct ci_hdrc *ci)
+{
+	if (ci->ulpi) {
+		ulpi_unregister_interface(ci->ulpi);
+		ci->ulpi = NULL;
+	}
+}
+
+int ci_ulpi_resume(struct ci_hdrc *ci)
+{
+	int cnt = 100000;
+
+	if (ci->platdata->phy_mode != USBPHY_INTERFACE_MODE_ULPI)
+		return 0;
+
+	while (cnt-- > 0) {
+		if (hw_read(ci, OP_ULPI_VIEWPORT, ULPI_SYNC_STATE))
+			return 0;
+		udelay(1);
+	}
+
+	return -ETIMEDOUT;
+}