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, 495 insertions, 0 deletions

diff --git a/scripts/dtc/util.c b/scripts/dtc/util.c
new file mode 100644
index 000000000..412592320
--- /dev/null
+++ b/scripts/dtc/util.c
@@ -0,0 +1,495 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright 2011 The Chromium Authors, All Rights Reserved.
+ * Copyright 2008 Jon Loeliger, Freescale Semiconductor, Inc.
+ *
+ * util_is_printable_string contributed by
+ *	Pantelis Antoniou <pantelis.antoniou AT gmail.com>
+ */
+
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <string.h>
+#include <assert.h>
+#include <inttypes.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "libfdt.h"
+#include "util.h"
+#include "version_gen.h"
+
+void fprint_path_escaped(FILE *fp, const char *path)
+{
+	const char *p = path;
+
+	while (*p) {
+		if (*p == ' ') {
+			fputc('\\', fp);
+			fputc(' ', fp);
+		} else {
+			fputc(*p, fp);
+		}
+
+		p++;
+	}
+}
+
+char *xstrdup(const char *s)
+{
+	int len = strlen(s) + 1;
+	char *d = xmalloc(len);
+
+	memcpy(d, s, len);
+
+	return d;
+}
+
+char *xstrndup(const char *s, size_t n)
+{
+	size_t len = strnlen(s, n) + 1;
+	char *d = xmalloc(len);
+
+	memcpy(d, s, len - 1);
+	d[len - 1] = '\0';
+
+	return d;
+}
+
+int xavsprintf_append(char **strp, const char *fmt, va_list ap)
+{
+	int n, size = 0;	/* start with 128 bytes */
+	char *p;
+	va_list ap_copy;
+
+	p = *strp;
+	if (p)
+		size = strlen(p);
+
+	va_copy(ap_copy, ap);
+	n = vsnprintf(NULL, 0, fmt, ap_copy) + 1;
+	va_end(ap_copy);
+
+	p = xrealloc(p, size + n);
+
+	n = vsnprintf(p + size, n, fmt, ap);
+
+	*strp = p;
+	return strlen(p);
+}
+
+int xasprintf_append(char **strp, const char *fmt, ...)
+{
+	int n;
+	va_list ap;
+
+	va_start(ap, fmt);
+	n = xavsprintf_append(strp, fmt, ap);
+	va_end(ap);
+
+	return n;
+}
+
+int xasprintf(char **strp, const char *fmt, ...)
+{
+	int n;
+	va_list ap;
+
+	*strp = NULL;
+
+	va_start(ap, fmt);
+	n = xavsprintf_append(strp, fmt, ap);
+	va_end(ap);
+
+	return n;
+}
+
+char *join_path(const char *path, const char *name)
+{
+	int lenp = strlen(path);
+	int lenn = strlen(name);
+	int len;
+	int needslash = 1;
+	char *str;
+
+	len = lenp + lenn + 2;
+	if ((lenp > 0) && (path[lenp-1] == '/')) {
+		needslash = 0;
+		len--;
+	}
+
+	str = xmalloc(len);
+	memcpy(str, path, lenp);
+	if (needslash) {
+		str[lenp] = '/';
+		lenp++;
+	}
+	memcpy(str+lenp, name, lenn+1);
+	return str;
+}
+
+bool util_is_printable_string(const void *data, int len)
+{
+	const char *s = data;
+	const char *ss, *se;
+
+	/* zero length is not */
+	if (len == 0)
+		return 0;
+
+	/* must terminate with zero */
+	if (s[len - 1] != '\0')
+		return 0;
+
+	se = s + len;
+
+	while (s < se) {
+		ss = s;
+		while (s < se && *s && isprint((unsigned char)*s))
+			s++;
+
+		/* not zero, or not done yet */
+		if (*s != '\0' || s == ss)
+			return 0;
+
+		s++;
+	}
+
+	return 1;
+}
+
+/*
+ * Parse a octal encoded character starting at index i in string s.  The
+ * resulting character will be returned and the index i will be updated to
+ * point at the character directly after the end of the encoding, this may be
+ * the '\0' terminator of the string.
+ */
+static char get_oct_char(const char *s, int *i)
+{
+	char x[4];
+	char *endx;
+	long val;
+
+	x[3] = '\0';
+	strncpy(x, s + *i, 3);
+
+	val = strtol(x, &endx, 8);
+
+	assert(endx > x);
+
+	(*i) += endx - x;
+	return val;
+}
+
+/*
+ * Parse a hexadecimal encoded character starting at index i in string s.  The
+ * resulting character will be returned and the index i will be updated to
+ * point at the character directly after the end of the encoding, this may be
+ * the '\0' terminator of the string.
+ */
+static char get_hex_char(const char *s, int *i)
+{
+	char x[3];
+	char *endx;
+	long val;
+
+	x[2] = '\0';
+	strncpy(x, s + *i, 2);
+
+	val = strtol(x, &endx, 16);
+	if (!(endx  > x))
+		die("\\x used with no following hex digits\n");
+
+	(*i) += endx - x;
+	return val;
+}
+
+char get_escape_char(const char *s, int *i)
+{
+	char	c = s[*i];
+	int	j = *i + 1;
+	char	val;
+
+	switch (c) {
+	case 'a':
+		val = '\a';
+		break;
+	case 'b':
+		val = '\b';
+		break;
+	case 't':
+		val = '\t';
+		break;
+	case 'n':
+		val = '\n';
+		break;
+	case 'v':
+		val = '\v';
+		break;
+	case 'f':
+		val = '\f';
+		break;
+	case 'r':
+		val = '\r';
+		break;
+	case '0':
+	case '1':
+	case '2':
+	case '3':
+	case '4':
+	case '5':
+	case '6':
+	case '7':
+		j--; /* need to re-read the first digit as
+		      * part of the octal value */
+		val = get_oct_char(s, &j);
+		break;
+	case 'x':
+		val = get_hex_char(s, &j);
+		break;
+	default:
+		val = c;
+	}
+
+	(*i) = j;
+	return val;
+}
+
+int utilfdt_read_err(const char *filename, char **buffp, size_t *len)
+{
+	int fd = 0;	/* assume stdin */
+	char *buf = NULL;
+	size_t bufsize = 1024, offset = 0;
+	int ret = 0;
+
+	*buffp = NULL;
+	if (strcmp(filename, "-") != 0) {
+		fd = open(filename, O_RDONLY);
+		if (fd < 0)
+			return errno;
+	}
+
+	/* Loop until we have read everything */
+	buf = xmalloc(bufsize);
+	do {
+		/* Expand the buffer to hold the next chunk */
+		if (offset == bufsize) {
+			bufsize *= 2;
+			buf = xrealloc(buf, bufsize);
+		}
+
+		ret = read(fd, &buf[offset], bufsize - offset);
+		if (ret < 0) {
+			ret = errno;
+			break;
+		}
+		offset += ret;
+	} while (ret != 0);
+
+	/* Clean up, including closing stdin; return errno on error */
+	close(fd);
+	if (ret)
+		free(buf);
+	else
+		*buffp = buf;
+	if (len)
+		*len = bufsize;
+	return ret;
+}
+
+char *utilfdt_read(const char *filename, size_t *len)
+{
+	char *buff;
+	int ret = utilfdt_read_err(filename, &buff, len);
+
+	if (ret) {
+		fprintf(stderr, "Couldn't open blob from '%s': %s\n", filename,
+			strerror(ret));
+		return NULL;
+	}
+	/* Successful read */
+	return buff;
+}
+
+int utilfdt_write_err(const char *filename, const void *blob)
+{
+	int fd = 1;	/* assume stdout */
+	int totalsize;
+	int offset;
+	int ret = 0;
+	const char *ptr = blob;
+
+	if (strcmp(filename, "-") != 0) {
+		fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0666);
+		if (fd < 0)
+			return errno;
+	}
+
+	totalsize = fdt_totalsize(blob);
+	offset = 0;
+
+	while (offset < totalsize) {
+		ret = write(fd, ptr + offset, totalsize - offset);
+		if (ret < 0) {
+			ret = -errno;
+			break;
+		}
+		offset += ret;
+	}
+	/* Close the file/stdin; return errno on error */
+	if (fd != 1)
+		close(fd);
+	return ret < 0 ? -ret : 0;
+}
+
+
+int utilfdt_write(const char *filename, const void *blob)
+{
+	int ret = utilfdt_write_err(filename, blob);
+
+	if (ret) {
+		fprintf(stderr, "Couldn't write blob to '%s': %s\n", filename,
+			strerror(ret));
+	}
+	return ret ? -1 : 0;
+}
+
+int utilfdt_decode_type(const char *fmt, int *type, int *size)
+{
+	int qualifier = 0;
+
+	if (!*fmt)
+		return -1;
+
+	/* get the conversion qualifier */
+	*size = -1;
+	if (strchr("hlLb", *fmt)) {
+		qualifier = *fmt++;
+		if (qualifier == *fmt) {
+			switch (*fmt++) {
+/* TODO:		case 'l': qualifier = 'L'; break;*/
+			case 'h':
+				qualifier = 'b';
+				break;
+			}
+		}
+	}
+
+	/* we should now have a type */
+	if ((*fmt == '\0') || !strchr("iuxsr", *fmt))
+		return -1;
+
+	/* convert qualifier (bhL) to byte size */
+	if (*fmt != 's' && *fmt != 'r')
+		*size = qualifier == 'b' ? 1 :
+				qualifier == 'h' ? 2 :
+				qualifier == 'l' ? 4 : -1;
+	*type = *fmt++;
+
+	/* that should be it! */
+	if (*fmt)
+		return -1;
+	return 0;
+}
+
+void utilfdt_print_data(const char *data, int len)
+{
+	int i;
+	const char *s;
+
+	/* no data, don't print */
+	if (len == 0)
+		return;
+
+	if (util_is_printable_string(data, len)) {
+		printf(" = ");
+
+		s = data;
+		do {
+			printf("\"%s\"", s);
+			s += strlen(s) + 1;
+			if (s < data + len)
+				printf(", ");
+		} while (s < data + len);
+
+	} else if ((len % 4) == 0) {
+		const fdt32_t *cell = (const fdt32_t *)data;
+
+		printf(" = <");
+		for (i = 0, len /= 4; i < len; i++)
+			printf("0x%08" PRIx32 "%s", fdt32_to_cpu(cell[i]),
+			       i < (len - 1) ? " " : "");
+		printf(">");
+	} else {
+		const unsigned char *p = (const unsigned char *)data;
+		printf(" = [");
+		for (i = 0; i < len; i++)
+			printf("%02x%s", *p++, i < len - 1 ? " " : "");
+		printf("]");
+	}
+}
+
+void NORETURN util_version(void)
+{
+	printf("Version: %s\n", DTC_VERSION);
+	exit(0);
+}
+
+void NORETURN util_usage(const char *errmsg, const char *synopsis,
+			 const char *short_opts,
+			 struct option const long_opts[],
+			 const char * const opts_help[])
+{
+	FILE *fp = errmsg ? stderr : stdout;
+	const char a_arg[] = "<arg>";
+	size_t a_arg_len = strlen(a_arg) + 1;
+	size_t i;
+	int optlen;
+
+	fprintf(fp,
+		"Usage: %s\n"
+		"\n"
+		"Options: -[%s]\n", synopsis, short_opts);
+
+	/* prescan the --long opt length to auto-align */
+	optlen = 0;
+	for (i = 0; long_opts[i].name; ++i) {
+		/* +1 is for space between --opt and help text */
+		int l = strlen(long_opts[i].name) + 1;
+		if (long_opts[i].has_arg == a_argument)
+			l += a_arg_len;
+		if (optlen < l)
+			optlen = l;
+	}
+
+	for (i = 0; long_opts[i].name; ++i) {
+		/* helps when adding new applets or options */
+		assert(opts_help[i] != NULL);
+
+		/* first output the short flag if it has one */
+		if (long_opts[i].val > '~')
+			fprintf(fp, "      ");
+		else
+			fprintf(fp, "  -%c, ", long_opts[i].val);
+
+		/* then the long flag */
+		if (long_opts[i].has_arg == no_argument)
+			fprintf(fp, "--%-*s", optlen, long_opts[i].name);
+		else
+			fprintf(fp, "--%s %s%*s", long_opts[i].name, a_arg,
+				(int)(optlen - strlen(long_opts[i].name) - a_arg_len), "");
+
+		/* finally the help text */
+		fprintf(fp, "%s\n", opts_help[i]);
+	}
+
+	if (errmsg) {
+		fprintf(fp, "\nError: %s\n", errmsg);
+		exit(EXIT_FAILURE);
+	} else
+		exit(EXIT_SUCCESS);
+}