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, 239 insertions, 0 deletions

diff --git a/drivers/hid/hid-icade.c b/drivers/hid/hid-icade.c
new file mode 100644
index 000000000..f3716cfac
--- /dev/null
+++ b/drivers/hid/hid-icade.c
@@ -0,0 +1,239 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  ION iCade input driver
+ *
+ *  Copyright (c) 2012 Bastien Nocera <hadess@hadess.net>
+ *  Copyright (c) 2012 Benjamin Tissoires <benjamin.tissoires@gmail.com>
+ */
+
+/*
+ */
+
+#include <linux/device.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+/*
+ *   ↑      A C Y L
+ *  ← →
+ *   ↓      B X Z R
+ *
+ *
+ *  UP ON,OFF  = w,e
+ *  RT ON,OFF  = d,c
+ *  DN ON,OFF  = x,z
+ *  LT ON,OFF  = a,q
+ *  A  ON,OFF  = y,t
+ *  B  ON,OFF  = h,r
+ *  C  ON,OFF  = u,f
+ *  X  ON,OFF  = j,n
+ *  Y  ON,OFF  = i,m
+ *  Z  ON,OFF  = k,p
+ *  L  ON,OFF  = o,g
+ *  R  ON,OFF  = l,v
+ */
+
+/* The translation code uses HID usage instead of input layer
+ * keys. This code generates a lookup table that makes
+ * translation quick.
+ *
+ * #include <linux/input.h>
+ * #include <stdio.h>
+ * #include <assert.h>
+ *
+ * #define unk     KEY_UNKNOWN
+ *
+ * < copy of hid_keyboard[] from hid-input.c >
+ *
+ * struct icade_key_translation {
+ *     int         from;
+ *     const char *to;
+ *     int         press;
+ * };
+ *
+ * static const struct icade_key_translation icade_keys[] = {
+ *    { KEY_W,        "KEY_UP",         1 },
+ *    { KEY_E,        "KEY_UP",         0 },
+ *    { KEY_D,        "KEY_RIGHT",      1 },
+ *    { KEY_C,        "KEY_RIGHT",      0 },
+ *    { KEY_X,        "KEY_DOWN",       1 },
+ *    { KEY_Z,        "KEY_DOWN",       0 },
+ *    { KEY_A,        "KEY_LEFT",       1 },
+ *    { KEY_Q,        "KEY_LEFT",       0 },
+ *    { KEY_Y,        "BTN_A",          1 },
+ *    { KEY_T,        "BTN_A",          0 },
+ *    { KEY_H,        "BTN_B",          1 },
+ *    { KEY_R,        "BTN_B",          0 },
+ *    { KEY_U,        "BTN_C",          1 },
+ *    { KEY_F,        "BTN_C",          0 },
+ *    { KEY_J,        "BTN_X",          1 },
+ *    { KEY_N,        "BTN_X",          0 },
+ *    { KEY_I,        "BTN_Y",          1 },
+ *    { KEY_M,        "BTN_Y",          0 },
+ *    { KEY_K,        "BTN_Z",          1 },
+ *    { KEY_P,        "BTN_Z",          0 },
+ *    { KEY_O,        "BTN_THUMBL",     1 },
+ *    { KEY_G,        "BTN_THUMBL",     0 },
+ *    { KEY_L,        "BTN_THUMBR",     1 },
+ *    { KEY_V,        "BTN_THUMBR",     0 },
+ *
+ *    { }
+ * };
+ *
+ * static int
+ * usage_for_key (int key)
+ * {
+ *     int i;
+ *     for (i = 0; i < 256; i++) {
+ *     if (hid_keyboard[i] == key)
+ *         return i;
+ *     }
+ *     assert(0);
+ * }
+ *
+ * int main (int argc, char **argv)
+ * {
+ *     const struct icade_key_translation *trans;
+ *     int max_usage = 0;
+ *
+ *     for (trans = icade_keys; trans->from; trans++) {
+ *         int usage = usage_for_key (trans->from);
+ *         max_usage = usage > max_usage ? usage : max_usage;
+ *     }
+ *
+ *     printf ("#define ICADE_MAX_USAGE %d\n\n", max_usage);
+ *     printf ("struct icade_key {\n");
+ *     printf ("\tu16 to;\n");
+ *     printf ("\tu8 press:1;\n");
+ *     printf ("};\n\n");
+ *     printf ("static const struct icade_key "
+ *             "icade_usage_table[%d] = {\n", max_usage + 1);
+ *     for (trans = icade_keys; trans->from; trans++) {
+ *         printf ("\t[%d] = { %s, %d },\n",
+ *                 usage_for_key (trans->from), trans->to, trans->press);
+ *     }
+ *     printf ("};\n");
+ *
+ *     return 0;
+ * }
+ */
+
+#define ICADE_MAX_USAGE 29
+
+struct icade_key {
+	u16 to;
+	u8 press:1;
+};
+
+static const struct icade_key icade_usage_table[30] = {
+	[26] = { KEY_UP, 1 },
+	[8] = { KEY_UP, 0 },
+	[7] = { KEY_RIGHT, 1 },
+	[6] = { KEY_RIGHT, 0 },
+	[27] = { KEY_DOWN, 1 },
+	[29] = { KEY_DOWN, 0 },
+	[4] = { KEY_LEFT, 1 },
+	[20] = { KEY_LEFT, 0 },
+	[28] = { BTN_A, 1 },
+	[23] = { BTN_A, 0 },
+	[11] = { BTN_B, 1 },
+	[21] = { BTN_B, 0 },
+	[24] = { BTN_C, 1 },
+	[9] = { BTN_C, 0 },
+	[13] = { BTN_X, 1 },
+	[17] = { BTN_X, 0 },
+	[12] = { BTN_Y, 1 },
+	[16] = { BTN_Y, 0 },
+	[14] = { BTN_Z, 1 },
+	[19] = { BTN_Z, 0 },
+	[18] = { BTN_THUMBL, 1 },
+	[10] = { BTN_THUMBL, 0 },
+	[15] = { BTN_THUMBR, 1 },
+	[25] = { BTN_THUMBR, 0 },
+};
+
+static const struct icade_key *icade_find_translation(u16 from)
+{
+	if (from > ICADE_MAX_USAGE)
+		return NULL;
+	return &icade_usage_table[from];
+}
+
+static int icade_event(struct hid_device *hdev, struct hid_field *field,
+		struct hid_usage *usage, __s32 value)
+{
+	const struct icade_key *trans;
+
+	if (!(hdev->claimed & HID_CLAIMED_INPUT) || !field->hidinput ||
+			!usage->type)
+		return 0;
+
+	/* We ignore the fake key up, and act only on key down */
+	if (!value)
+		return 1;
+
+	trans = icade_find_translation(usage->hid & HID_USAGE);
+
+	if (!trans)
+		return 1;
+
+	input_event(field->hidinput->input, usage->type,
+			trans->to, trans->press);
+
+	return 1;
+}
+
+static int icade_input_mapping(struct hid_device *hdev, struct hid_input *hi,
+		struct hid_field *field, struct hid_usage *usage,
+		unsigned long **bit, int *max)
+{
+	const struct icade_key *trans;
+
+	if ((usage->hid & HID_USAGE_PAGE) == HID_UP_KEYBOARD) {
+		trans = icade_find_translation(usage->hid & HID_USAGE);
+
+		if (!trans)
+			return -1;
+
+		hid_map_usage(hi, usage, bit, max, EV_KEY, trans->to);
+		set_bit(trans->to, hi->input->keybit);
+
+		return 1;
+	}
+
+	/* ignore others */
+	return -1;
+
+}
+
+static int icade_input_mapped(struct hid_device *hdev, struct hid_input *hi,
+		struct hid_field *field, struct hid_usage *usage,
+		unsigned long **bit, int *max)
+{
+	if (usage->type == EV_KEY)
+		set_bit(usage->type, hi->input->evbit);
+
+	return -1;
+}
+
+static const struct hid_device_id icade_devices[] = {
+	{ HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_ION, USB_DEVICE_ID_ICADE) },
+
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, icade_devices);
+
+static struct hid_driver icade_driver = {
+	.name = "icade",
+	.id_table = icade_devices,
+	.event = icade_event,
+	.input_mapped = icade_input_mapped,
+	.input_mapping = icade_input_mapping,
+};
+module_hid_driver(icade_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Bastien Nocera <hadess@hadess.net>");
+MODULE_DESCRIPTION("ION iCade input driver");