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, 348 insertions, 0 deletions

diff --git a/scripts/dtc/fdtput.c b/scripts/dtc/fdtput.c
new file mode 100644
index 000000000..a363c3cab
--- /dev/null
+++ b/scripts/dtc/fdtput.c
@@ -0,0 +1,348 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
+ */
+
+#include <assert.h>
+#include <ctype.h>
+#include <getopt.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <libfdt.h>
+
+#include "util.h"
+
+/* These are the operations we support */
+enum oper_type {
+	OPER_WRITE_PROP,		/* Write a property in a node */
+	OPER_CREATE_NODE,		/* Create a new node */
+};
+
+struct display_info {
+	enum oper_type oper;	/* operation to perform */
+	int type;		/* data type (s/i/u/x or 0 for default) */
+	int size;		/* data size (1/2/4) */
+	int verbose;		/* verbose output */
+	int auto_path;		/* automatically create all path components */
+};
+
+
+/**
+ * Report an error with a particular node.
+ *
+ * @param name		Node name to report error on
+ * @param namelen	Length of node name, or -1 to use entire string
+ * @param err		Error number to report (-FDT_ERR_...)
+ */
+static void report_error(const char *name, int namelen, int err)
+{
+	if (namelen == -1)
+		namelen = strlen(name);
+	fprintf(stderr, "Error at '%1.*s': %s\n", namelen, name,
+		fdt_strerror(err));
+}
+
+/**
+ * Encode a series of arguments in a property value.
+ *
+ * @param disp		Display information / options
+ * @param arg		List of arguments from command line
+ * @param arg_count	Number of arguments (may be 0)
+ * @param valuep	Returns buffer containing value
+ * @param *value_len	Returns length of value encoded
+ */
+static int encode_value(struct display_info *disp, char **arg, int arg_count,
+			char **valuep, int *value_len)
+{
+	char *value = NULL;	/* holding area for value */
+	int value_size = 0;	/* size of holding area */
+	char *ptr;		/* pointer to current value position */
+	int len;		/* length of this cell/string/byte */
+	int ival;
+	int upto;	/* the number of bytes we have written to buf */
+	char fmt[3];
+
+	upto = 0;
+
+	if (disp->verbose)
+		fprintf(stderr, "Decoding value:\n");
+
+	fmt[0] = '%';
+	fmt[1] = disp->type ? disp->type : 'd';
+	fmt[2] = '\0';
+	for (; arg_count > 0; arg++, arg_count--, upto += len) {
+		/* assume integer unless told otherwise */
+		if (disp->type == 's')
+			len = strlen(*arg) + 1;
+		else
+			len = disp->size == -1 ? 4 : disp->size;
+
+		/* enlarge our value buffer by a suitable margin if needed */
+		if (upto + len > value_size) {
+			value_size = (upto + len) + 500;
+			value = realloc(value, value_size);
+			if (!value) {
+				fprintf(stderr, "Out of mmory: cannot alloc "
+					"%d bytes\n", value_size);
+				return -1;
+			}
+		}
+
+		ptr = value + upto;
+		if (disp->type == 's') {
+			memcpy(ptr, *arg, len);
+			if (disp->verbose)
+				fprintf(stderr, "\tstring: '%s'\n", ptr);
+		} else {
+			int *iptr = (int *)ptr;
+			sscanf(*arg, fmt, &ival);
+			if (len == 4)
+				*iptr = cpu_to_fdt32(ival);
+			else
+				*ptr = (uint8_t)ival;
+			if (disp->verbose) {
+				fprintf(stderr, "\t%s: %d\n",
+					disp->size == 1 ? "byte" :
+					disp->size == 2 ? "short" : "int",
+					ival);
+			}
+		}
+	}
+	*value_len = upto;
+	*valuep = value;
+	if (disp->verbose)
+		fprintf(stderr, "Value size %d\n", upto);
+	return 0;
+}
+
+static int store_key_value(void *blob, const char *node_name,
+		const char *property, const char *buf, int len)
+{
+	int node;
+	int err;
+
+	node = fdt_path_offset(blob, node_name);
+	if (node < 0) {
+		report_error(node_name, -1, node);
+		return -1;
+	}
+
+	err = fdt_setprop(blob, node, property, buf, len);
+	if (err) {
+		report_error(property, -1, err);
+		return -1;
+	}
+	return 0;
+}
+
+/**
+ * Create paths as needed for all components of a path
+ *
+ * Any components of the path that do not exist are created. Errors are
+ * reported.
+ *
+ * @param blob		FDT blob to write into
+ * @param in_path	Path to process
+ * @return 0 if ok, -1 on error
+ */
+static int create_paths(void *blob, const char *in_path)
+{
+	const char *path = in_path;
+	const char *sep;
+	int node, offset = 0;
+
+	/* skip leading '/' */
+	while (*path == '/')
+		path++;
+
+	for (sep = path; *sep; path = sep + 1, offset = node) {
+		/* equivalent to strchrnul(), but it requires _GNU_SOURCE */
+		sep = strchr(path, '/');
+		if (!sep)
+			sep = path + strlen(path);
+
+		node = fdt_subnode_offset_namelen(blob, offset, path,
+				sep - path);
+		if (node == -FDT_ERR_NOTFOUND) {
+			node = fdt_add_subnode_namelen(blob, offset, path,
+						       sep - path);
+		}
+		if (node < 0) {
+			report_error(path, sep - path, node);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+/**
+ * Create a new node in the fdt.
+ *
+ * This will overwrite the node_name string. Any error is reported.
+ *
+ * TODO: Perhaps create fdt_path_offset_namelen() so we don't need to do this.
+ *
+ * @param blob		FDT blob to write into
+ * @param node_name	Name of node to create
+ * @return new node offset if found, or -1 on failure
+ */
+static int create_node(void *blob, const char *node_name)
+{
+	int node = 0;
+	char *p;
+
+	p = strrchr(node_name, '/');
+	if (!p) {
+		report_error(node_name, -1, -FDT_ERR_BADPATH);
+		return -1;
+	}
+	*p = '\0';
+
+	if (p > node_name) {
+		node = fdt_path_offset(blob, node_name);
+		if (node < 0) {
+			report_error(node_name, -1, node);
+			return -1;
+		}
+	}
+
+	node = fdt_add_subnode(blob, node, p + 1);
+	if (node < 0) {
+		report_error(p + 1, -1, node);
+		return -1;
+	}
+
+	return 0;
+}
+
+static int do_fdtput(struct display_info *disp, const char *filename,
+		    char **arg, int arg_count)
+{
+	char *value;
+	char *blob;
+	int len, ret = 0;
+
+	blob = utilfdt_read(filename);
+	if (!blob)
+		return -1;
+
+	switch (disp->oper) {
+	case OPER_WRITE_PROP:
+		/*
+		 * Convert the arguments into a single binary value, then
+		 * store them into the property.
+		 */
+		assert(arg_count >= 2);
+		if (disp->auto_path && create_paths(blob, *arg))
+			return -1;
+		if (encode_value(disp, arg + 2, arg_count - 2, &value, &len) ||
+			store_key_value(blob, *arg, arg[1], value, len))
+			ret = -1;
+		break;
+	case OPER_CREATE_NODE:
+		for (; ret >= 0 && arg_count--; arg++) {
+			if (disp->auto_path)
+				ret = create_paths(blob, *arg);
+			else
+				ret = create_node(blob, *arg);
+		}
+		break;
+	}
+	if (ret >= 0)
+		ret = utilfdt_write(filename, blob);
+
+	free(blob);
+	return ret;
+}
+
+static const char *usage_msg =
+	"fdtput - write a property value to a device tree\n"
+	"\n"
+	"The command line arguments are joined together into a single value.\n"
+	"\n"
+	"Usage:\n"
+	"	fdtput <options> <dt file> <node> <property> [<value>...]\n"
+	"	fdtput -c <options> <dt file> [<node>...]\n"
+	"Options:\n"
+	"\t-c\t\tCreate nodes if they don't already exist\n"
+	"\t-p\t\tAutomatically create nodes as needed for the node path\n"
+	"\t-t <type>\tType of data\n"
+	"\t-v\t\tVerbose: display each value decoded from command line\n"
+	"\t-h\t\tPrint this help\n\n"
+	USAGE_TYPE_MSG;
+
+static void usage(const char *msg)
+{
+	if (msg)
+		fprintf(stderr, "Error: %s\n\n", msg);
+
+	fprintf(stderr, "%s", usage_msg);
+	exit(2);
+}
+
+int main(int argc, char *argv[])
+{
+	struct display_info disp;
+	char *filename = NULL;
+
+	memset(&disp, '\0', sizeof(disp));
+	disp.size = -1;
+	disp.oper = OPER_WRITE_PROP;
+	for (;;) {
+		int c = getopt(argc, argv, "chpt:v");
+		if (c == -1)
+			break;
+
+		/*
+		 * TODO: add options to:
+		 * - delete property
+		 * - delete node (optionally recursively)
+		 * - rename node
+		 * - pack fdt before writing
+		 * - set amount of free space when writing
+		 * - expand fdt if value doesn't fit
+		 */
+		switch (c) {
+		case 'c':
+			disp.oper = OPER_CREATE_NODE;
+			break;
+		case 'h':
+		case '?':
+			usage(NULL);
+		case 'p':
+			disp.auto_path = 1;
+			break;
+		case 't':
+			if (utilfdt_decode_type(optarg, &disp.type,
+					&disp.size))
+				usage("Invalid type string");
+			break;
+
+		case 'v':
+			disp.verbose = 1;
+			break;
+		}
+	}
+
+	if (optind < argc)
+		filename = argv[optind++];
+	if (!filename)
+		usage("Missing filename");
+
+	argv += optind;
+	argc -= optind;
+
+	if (disp.oper == OPER_WRITE_PROP) {
+		if (argc < 1)
+			usage("Missing node");
+		if (argc < 2)
+			usage("Missing property");
+	}
+
+	if (do_fdtput(&disp, filename, argv, argc))
+		return 1;
+	return 0;
+}