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/hid/hid-evision.c b/drivers/hid/hid-evision.c
new file mode 100644
index 000000000..3e7f43ab8
--- /dev/null
+++ b/drivers/hid/hid-evision.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  HID driver for EVision devices
+ *  For now, only ignore bogus consumer reports
+ *  sent after the keyboard has been configured
+ *
+ *  Copyright (c) 2022 Philippe Valembois
+ */
+
+#include <linux/device.h>
+#include <linux/input.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+static int evision_input_mapping(struct hid_device *hdev, struct hid_input *hi,
+		struct hid_field *field, struct hid_usage *usage,
+		unsigned long **bit, int *max)
+{
+	/* mapping only applies to USB_DEVICE_ID_EVISION_ICL01 */
+	if (hdev->product != USB_DEVICE_ID_EVISION_ICL01)
+		return 0;
+
+	if ((usage->hid & HID_USAGE_PAGE) != HID_UP_CONSUMER)
+		return 0;
+
+	/* Ignore key down event */
+	if ((usage->hid & HID_USAGE) >> 8 == 0x05)
+		return -1;
+	/* Ignore key up event */
+	if ((usage->hid & HID_USAGE) >> 8 == 0x06)
+		return -1;
+
+	switch (usage->hid & HID_USAGE) {
+	/* Ignore configuration saved event */
+	case 0x0401: return -1;
+	/* Ignore reset event */
+	case 0x0402: return -1;
+	}
+	return 0;
+}
+
+#define REP_DSC_SIZE 236
+#define USAGE_MAX_INDEX 59
+
+static const __u8 *evision_report_fixup(struct hid_device *hdev, __u8 *rdesc,
+		unsigned int *rsize)
+{
+	if (hdev->product == USB_DEVICE_ID_EV_TELINK_RECEIVER &&
+	    *rsize == REP_DSC_SIZE && rdesc[USAGE_MAX_INDEX] == 0x29 &&
+	    rdesc[USAGE_MAX_INDEX + 1] == 3) {
+		hid_info(hdev, "fixing EVision:TeLink Receiver report descriptor\n");
+		rdesc[USAGE_MAX_INDEX + 1] = 5; // change usage max from 3 to 5
+	}
+	return rdesc;
+}
+
+static const struct hid_device_id evision_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_EVISION, USB_DEVICE_ID_EVISION_ICL01) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_EVISION, USB_DEVICE_ID_EV_TELINK_RECEIVER) },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, evision_devices);
+
+static struct hid_driver evision_driver = {
+	.name = "evision",
+	.id_table = evision_devices,
+	.input_mapping = evision_input_mapping,
+	.report_fixup = evision_report_fixup,
+};
+module_hid_driver(evision_driver);
+
+MODULE_DESCRIPTION("HID driver for EVision devices");
+MODULE_LICENSE("GPL");