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, 209 insertions, 0 deletions

diff --git a/drivers/accessibility/speakup/keyhelp.c b/drivers/accessibility/speakup/keyhelp.c
new file mode 100644
index 000000000..822ceac83
--- /dev/null
+++ b/drivers/accessibility/speakup/keyhelp.c
@@ -0,0 +1,209 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* speakup_keyhelp.c
+ * help module for speakup
+ *
+ *written by David Borowski.
+ *
+ *  Copyright (C) 2003  David Borowski.
+ */
+
+#include <linux/keyboard.h>
+#include "spk_priv.h"
+#include "speakup.h"
+
+#define MAXFUNCS 130
+#define MAXKEYS 256
+static const int num_key_names = MSG_KEYNAMES_END - MSG_KEYNAMES_START + 1;
+static u_short key_offsets[MAXFUNCS], key_data[MAXKEYS];
+static u_short masks[] = { 32, 16, 8, 4, 2, 1 };
+
+static short letter_offsets[26] = {
+	-1, -1, -1, -1, -1, -1, -1, -1,
+	-1, -1, -1, -1, -1, -1, -1, -1,
+	-1, -1, -1, -1, -1, -1, -1, -1,
+	-1, -1 };
+
+static u_char funcvals[] = {
+	ATTRIB_BLEEP_DEC, ATTRIB_BLEEP_INC, BLEEPS_DEC, BLEEPS_INC,
+	SAY_FIRST_CHAR, SAY_LAST_CHAR, SAY_CHAR, SAY_CHAR_NUM,
+	SAY_NEXT_CHAR, SAY_PHONETIC_CHAR, SAY_PREV_CHAR, SPEAKUP_PARKED,
+	SPEAKUP_CUT, EDIT_DELIM, EDIT_EXNUM, EDIT_MOST,
+	EDIT_REPEAT, EDIT_SOME, SPEAKUP_GOTO, BOTTOM_EDGE,
+	LEFT_EDGE, RIGHT_EDGE, TOP_EDGE, SPEAKUP_HELP,
+	SAY_LINE, SAY_NEXT_LINE, SAY_PREV_LINE, SAY_LINE_INDENT,
+	SPEAKUP_PASTE, PITCH_DEC, PITCH_INC, PUNCT_DEC,
+	PUNCT_INC, PUNC_LEVEL_DEC, PUNC_LEVEL_INC, SPEAKUP_QUIET,
+	RATE_DEC, RATE_INC, READING_PUNC_DEC, READING_PUNC_INC,
+	SAY_ATTRIBUTES, SAY_FROM_LEFT, SAY_FROM_TOP, SAY_POSITION,
+	SAY_SCREEN, SAY_TO_BOTTOM, SAY_TO_RIGHT, SPK_KEY,
+	SPK_LOCK, SPEAKUP_OFF, SPEECH_KILL, SPELL_DELAY_DEC,
+	SPELL_DELAY_INC, SPELL_WORD, SPELL_PHONETIC, TONE_DEC,
+	TONE_INC, VOICE_DEC, VOICE_INC, VOL_DEC,
+	VOL_INC, CLEAR_WIN, SAY_WIN, SET_WIN,
+	ENABLE_WIN, SAY_WORD, SAY_NEXT_WORD, SAY_PREV_WORD, 0
+};
+
+static u_char *state_tbl;
+static int cur_item, nstates;
+
+static void build_key_data(void)
+{
+	u_char *kp, counters[MAXFUNCS], ch, ch1;
+	u_short *p_key, key;
+	int i, offset = 1;
+
+	nstates = (int)(state_tbl[-1]);
+	memset(counters, 0, sizeof(counters));
+	memset(key_offsets, 0, sizeof(key_offsets));
+	kp = state_tbl + nstates + 1;
+	while (*kp++) {
+		/* count occurrences of each function */
+		for (i = 0; i < nstates; i++, kp++) {
+			if (!*kp)
+				continue;
+			if ((state_tbl[i] & 16) != 0 && *kp == SPK_KEY)
+				continue;
+			counters[*kp]++;
+		}
+	}
+	for (i = 0; i < MAXFUNCS; i++) {
+		if (counters[i] == 0)
+			continue;
+		key_offsets[i] = offset;
+		offset += (counters[i] + 1);
+		if (offset >= MAXKEYS)
+			break;
+	}
+/* leave counters set so high keycodes come first.
+ * this is done so num pad and other extended keys maps are spoken before
+ * the alpha with speakup type mapping.
+ */
+	kp = state_tbl + nstates + 1;
+	while ((ch = *kp++)) {
+		for (i = 0; i < nstates; i++) {
+			ch1 = *kp++;
+			if (!ch1)
+				continue;
+			if ((state_tbl[i] & 16) != 0 && ch1 == SPK_KEY)
+				continue;
+			key = (state_tbl[i] << 8) + ch;
+			counters[ch1]--;
+			offset = key_offsets[ch1];
+			if (!offset)
+				continue;
+			p_key = key_data + offset + counters[ch1];
+			*p_key = key;
+		}
+	}
+}
+
+static void say_key(int key)
+{
+	int i, state = key >> 8;
+
+	key &= 0xff;
+	for (i = 0; i < 6; i++) {
+		if (state & masks[i])
+			synth_printf(" %s", spk_msg_get(MSG_STATES_START + i));
+	}
+	if ((key > 0) && (key <= num_key_names))
+		synth_printf(" %s\n",
+			     spk_msg_get(MSG_KEYNAMES_START + (key - 1)));
+}
+
+static int help_init(void)
+{
+	char start = SPACE;
+	int i;
+	int num_funcs = MSG_FUNCNAMES_END - MSG_FUNCNAMES_START + 1;
+
+	state_tbl = spk_our_keys[0] + SHIFT_TBL_SIZE + 2;
+	for (i = 0; i < num_funcs; i++) {
+		char *cur_funcname = spk_msg_get(MSG_FUNCNAMES_START + i);
+
+		if (start == *cur_funcname)
+			continue;
+		start = *cur_funcname;
+		letter_offsets[(start & 31) - 1] = i;
+	}
+	return 0;
+}
+
+int spk_handle_help(struct vc_data *vc, u_char type, u_char ch, u_short key)
+{
+	int i, n;
+	char *name;
+	u_char func, *kp;
+	u_short *p_keys, val;
+
+	if (letter_offsets[0] == -1)
+		help_init();
+	if (type == KT_LATIN) {
+		if (ch == SPACE) {
+			spk_special_handler = NULL;
+			synth_printf("%s\n", spk_msg_get(MSG_LEAVING_HELP));
+			return 1;
+		}
+		ch |= 32; /* lower case */
+		if (ch < 'a' || ch > 'z')
+			return -1;
+		if (letter_offsets[ch - 'a'] == -1) {
+			synth_printf(spk_msg_get(MSG_NO_COMMAND), ch);
+			synth_printf("\n");
+			return 1;
+		}
+		cur_item = letter_offsets[ch - 'a'];
+	} else if (type == KT_CUR) {
+		if (ch == 0 &&
+		    (MSG_FUNCNAMES_START + cur_item + 1) <= MSG_FUNCNAMES_END)
+			cur_item++;
+		else if (ch == 3 && cur_item > 0)
+			cur_item--;
+		else
+			return -1;
+	} else if (type == KT_SPKUP && ch == SPEAKUP_HELP &&
+		   !spk_special_handler) {
+		spk_special_handler = spk_handle_help;
+		synth_printf("%s\n", spk_msg_get(MSG_HELP_INFO));
+		build_key_data(); /* rebuild each time in case new mapping */
+		return 1;
+	} else {
+		name = NULL;
+		if ((type != KT_SPKUP) && (key > 0) && (key <= num_key_names)) {
+			synth_printf("%s\n",
+				     spk_msg_get(MSG_KEYNAMES_START + key - 1));
+			return 1;
+		}
+		for (i = 0; funcvals[i] != 0 && !name; i++) {
+			if (ch == funcvals[i])
+				name = spk_msg_get(MSG_FUNCNAMES_START + i);
+		}
+		if (!name)
+			return -1;
+		kp = spk_our_keys[key] + 1;
+		for (i = 0; i < nstates; i++) {
+			if (ch == kp[i])
+				break;
+		}
+		key += (state_tbl[i] << 8);
+		say_key(key);
+		synth_printf(spk_msg_get(MSG_KEYDESC), name);
+		synth_printf("\n");
+		return 1;
+	}
+	name = spk_msg_get(MSG_FUNCNAMES_START + cur_item);
+	func = funcvals[cur_item];
+	synth_printf("%s", name);
+	if (key_offsets[func] == 0) {
+		synth_printf(" %s\n", spk_msg_get(MSG_IS_UNASSIGNED));
+		return 1;
+	}
+	p_keys = key_data + key_offsets[func];
+	for (n = 0; p_keys[n]; n++) {
+		val = p_keys[n];
+		if (n > 0)
+			synth_printf("%s ", spk_msg_get(MSG_DISJUNCTION));
+		say_key(val);
+	}
+	return 1;
+}