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, 161 insertions, 0 deletions

diff --git a/drivers/accessibility/speakup/genmap.c b/drivers/accessibility/speakup/genmap.c
new file mode 100644
index 000000000..0882bab10
--- /dev/null
+++ b/drivers/accessibility/speakup/genmap.c
@@ -0,0 +1,161 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* genmap.c
+ * originally written by: Kirk Reiser.
+ *
+ ** Copyright (C) 2002  Kirk Reiser.
+ *  Copyright (C) 2003  David Borowski.
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <libgen.h>
+#include <string.h>
+#include <ctype.h>
+#include "utils.h"
+
+struct st_key_init {
+	char *name;
+	int value, shift;
+};
+
+static unsigned char key_data[MAXKEYVAL][16], *kp;
+
+#include "mapdata.h"
+
+static const char delims[] = "\t\n ";
+static char *cp;
+static int map_ver = 119; /* an arbitrary number so speakup can check */
+static int shift_table[17];
+static int max_states = 1, flags;
+/* flags reserved for later, maybe for individual console maps */
+
+static int get_shift_value(int state)
+{
+	int i;
+
+	for (i = 0; shift_table[i] != state; i++) {
+		if (shift_table[i] == -1) {
+			if (i >= 16)
+				oops("too many shift states", NULL);
+			shift_table[i] = state;
+			max_states = i+1;
+		break;
+	}
+	}
+	return i;
+}
+
+int
+main(int argc, char *argv[])
+{
+	int value, shift_state, i, spk_val = 0, lock_val = 0;
+	int max_key_used = 0, num_keys_used = 0;
+	struct st_key *this;
+	struct st_key_init *p_init;
+	char buffer[256];
+
+	bzero(key_table, sizeof(key_table));
+	bzero(key_data, sizeof(key_data));
+
+	shift_table[0] = 0;
+	for (i = 1; i <= 16; i++)
+		shift_table[i] = -1;
+
+	if (argc < 2) {
+		fputs("usage: genmap filename\n", stderr);
+		exit(1);
+	}
+
+	for (p_init = init_key_data; p_init->name[0] != '.'; p_init++)
+		add_key(p_init->name, p_init->value, p_init->shift);
+
+	open_input(NULL, argv[1]);
+	while (fgets(buffer, sizeof(buffer), infile)) {
+		lc++;
+		value = shift_state = 0;
+
+		cp = strtok(buffer, delims);
+		if (*cp == '#')
+			continue;
+
+		while (cp) {
+			if (*cp == '=')
+				break;
+			this = find_key(cp);
+			if (this == NULL)
+				oops("unknown key/modifier", cp);
+			if (this->shift == is_shift) {
+				if (value)
+					oops("modifiers must come first", cp);
+				shift_state += this->value;
+			} else if (this->shift == is_input)
+				value = this->value;
+			else
+				oops("bad modifier or key", cp);
+			cp = strtok(0, delims);
+		}
+		if (!cp)
+			oops("no = found", NULL);
+
+		cp = strtok(0, delims);
+		if (!cp)
+			oops("no speakup function after =", NULL);
+
+		this = find_key(cp);
+		if (this == NULL || this->shift != is_spk)
+			oops("invalid speakup function", cp);
+
+		i = get_shift_value(shift_state);
+		if (key_data[value][i]) {
+			while (--cp > buffer)
+				if (!*cp)
+					*cp = ' ';
+			oops("two functions on same key combination", cp);
+		}
+		key_data[value][i] = (char)this->value;
+		if (value > max_key_used)
+			max_key_used = value;
+	}
+	fclose(infile);
+
+	this = find_key("spk_key");
+	if (this)
+		spk_val = this->value;
+
+	this = find_key("spk_lock");
+	if (this)
+		lock_val = this->value;
+
+	for (lc = 1; lc <= max_key_used; lc++) {
+		kp = key_data[lc];
+		if (!memcmp(key_data[0], kp, 16))
+			continue;
+		num_keys_used++;
+		for (i = 0; i < max_states; i++) {
+			if (kp[i] != spk_val && kp[i] != lock_val)
+				continue;
+			shift_state = shift_table[i];
+			if (shift_state&16)
+				continue;
+			shift_state = get_shift_value(shift_state+16);
+			kp[shift_state] = kp[i];
+			/* fill in so we can process the key up, as spk bit will be set */
+		}
+	}
+
+	printf("\t%d, %d, %d,\n\t", map_ver, num_keys_used, max_states);
+	for (i = 0; i < max_states; i++)
+		printf("%d, ", shift_table[i]);
+	printf("%d,", flags);
+	for (lc = 1; lc <= max_key_used; lc++) {
+		kp = key_data[lc];
+		if (!memcmp(key_data[0], kp, 16))
+			continue;
+		printf("\n\t%d,", lc);
+		for (i = 0; i < max_states; i++)
+			printf(" %d,", (unsigned int)kp[i]);
+	}
+	printf("\n\t0, %d\n", map_ver);
+
+	exit(0);
+}