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, 79 insertions, 0 deletions

diff --git a/drivers/hid/hid-speedlink.c b/drivers/hid/hid-speedlink.c
new file mode 100644
index 000000000..22ee078c4
--- /dev/null
+++ b/drivers/hid/hid-speedlink.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  HID driver for Speedlink Vicious and Divine Cezanne (USB mouse).
+ *  Fixes "jumpy" cursor and removes nonexistent keyboard LEDS from
+ *  the HID descriptor.
+ *
+ *  Copyright (c) 2011, 2013 Stefan Kriwanek <dev@stefankriwanek.de>
+ */
+
+/*
+ */
+
+#include <linux/device.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+static const struct hid_device_id speedlink_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_X_TENSIONS, USB_DEVICE_ID_SPEEDLINK_VAD_CEZANNE)},
+	{ }
+};
+
+static int speedlink_input_mapping(struct hid_device *hdev,
+		struct hid_input *hi,
+		struct hid_field *field, struct hid_usage *usage,
+		unsigned long **bit, int *max)
+{
+	/*
+	 * The Cezanne mouse has a second "keyboard" USB endpoint for it is
+	 * able to map keyboard events to the button presses.
+	 * It sends a standard keyboard report descriptor, though, whose
+	 * LEDs we ignore.
+	 */
+	switch (usage->hid & HID_USAGE_PAGE) {
+	case HID_UP_LED:
+		return -1;
+	}
+	return 0;
+}
+
+static int speedlink_event(struct hid_device *hdev, struct hid_field *field,
+		struct hid_usage *usage, __s32 value)
+{
+	/* No other conditions due to usage_table. */
+
+	/* This fixes the "jumpy" cursor occuring due to invalid events sent
+	 * by the device. Some devices only send them with value==+256, others
+	 * don't. However, catching abs(value)>=256 is restrictive enough not
+	 * to interfere with devices that were bug-free (has been tested).
+	 */
+	if (abs(value) >= 256)
+		return 1;
+	/* Drop useless distance 0 events (on button clicks etc.) as well */
+	if (value == 0)
+		return 1;
+
+	return 0;
+}
+
+MODULE_DEVICE_TABLE(hid, speedlink_devices);
+
+static const struct hid_usage_id speedlink_grabbed_usages[] = {
+	{ HID_GD_X, EV_REL, 0 },
+	{ HID_GD_Y, EV_REL, 1 },
+	{ HID_ANY_ID - 1, HID_ANY_ID - 1, HID_ANY_ID - 1}
+};
+
+static struct hid_driver speedlink_driver = {
+	.name = "speedlink",
+	.id_table = speedlink_devices,
+	.usage_table = speedlink_grabbed_usages,
+	.input_mapping = speedlink_input_mapping,
+	.event = speedlink_event,
+};
+module_hid_driver(speedlink_driver);
+
+MODULE_DESCRIPTION("HID driver for Speedlink Vicious and Divine Cezanne (USB mouse)");
+MODULE_LICENSE("GPL");