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, 437 insertions, 0 deletions

diff --git a/scripts/dtc/treesource.c b/scripts/dtc/treesource.c
new file mode 100644
index 000000000..bf648bf6c
--- /dev/null
+++ b/scripts/dtc/treesource.c
@@ -0,0 +1,437 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * (C) Copyright David Gibson <dwg@au1.ibm.com>, IBM Corporation.  2005.
+ */
+
+#include "dtc.h"
+#include "srcpos.h"
+
+extern FILE *yyin;
+extern int yyparse(void);
+extern YYLTYPE yylloc;
+
+struct dt_info *parser_output;
+bool treesource_error;
+
+struct dt_info *dt_from_source(const char *fname)
+{
+	parser_output = NULL;
+	treesource_error = false;
+
+	srcfile_push(fname);
+	yyin = current_srcfile->f;
+	yylloc.file = current_srcfile;
+
+	if (yyparse() != 0)
+		die("Unable to parse input tree\n");
+
+	if (treesource_error)
+		die("Syntax error parsing input tree\n");
+
+	return parser_output;
+}
+
+static void write_prefix(FILE *f, int level)
+{
+	int i;
+
+	for (i = 0; i < level; i++)
+		fputc('\t', f);
+}
+
+static bool isstring(char c)
+{
+	return (isprint((unsigned char)c)
+		|| (c == '\0')
+		|| strchr("\a\b\t\n\v\f\r", c));
+}
+
+static void write_propval_string(FILE *f, const char *s, size_t len)
+{
+	const char *end = s + len - 1;
+
+	if (!len)
+		return;
+
+	assert(*end == '\0');
+
+	fprintf(f, "\"");
+	while (s < end) {
+		char c = *s++;
+		switch (c) {
+		case '\a':
+			fprintf(f, "\\a");
+			break;
+		case '\b':
+			fprintf(f, "\\b");
+			break;
+		case '\t':
+			fprintf(f, "\\t");
+			break;
+		case '\n':
+			fprintf(f, "\\n");
+			break;
+		case '\v':
+			fprintf(f, "\\v");
+			break;
+		case '\f':
+			fprintf(f, "\\f");
+			break;
+		case '\r':
+			fprintf(f, "\\r");
+			break;
+		case '\\':
+			fprintf(f, "\\\\");
+			break;
+		case '\"':
+			fprintf(f, "\\\"");
+			break;
+		case '\0':
+			fprintf(f, "\\0");
+			break;
+		default:
+			if (isprint((unsigned char)c))
+				fprintf(f, "%c", c);
+			else
+				fprintf(f, "\\x%02"PRIx8, c);
+		}
+	}
+	fprintf(f, "\"");
+}
+
+static void write_propval_int(FILE *f, const char *p, size_t len, size_t width)
+{
+	const char *end = p + len;
+	assert(len % width == 0);
+
+	for (; p < end; p += width) {
+		switch (width) {
+		case 1:
+			fprintf(f, "%02"PRIx8, *(const uint8_t*)p);
+			break;
+		case 2:
+			fprintf(f, "0x%02"PRIx16, dtb_ld16(p));
+			break;
+		case 4:
+			fprintf(f, "0x%02"PRIx32, dtb_ld32(p));
+			break;
+		case 8:
+			fprintf(f, "0x%02"PRIx64, dtb_ld64(p));
+			break;
+		}
+		if (p + width < end)
+			fputc(' ', f);
+	}
+}
+
+static const char *delim_start[] = {
+	[TYPE_UINT8] = "[",
+	[TYPE_UINT16] = "/bits/ 16 <",
+	[TYPE_UINT32] = "<",
+	[TYPE_UINT64] = "/bits/ 64 <",
+	[TYPE_STRING] = "",
+};
+static const char *delim_end[] = {
+	[TYPE_UINT8] = "]",
+	[TYPE_UINT16] = ">",
+	[TYPE_UINT32] = ">",
+	[TYPE_UINT64] = ">",
+	[TYPE_STRING] = "",
+};
+
+/*
+ * The invariants in the marker list are:
+ *  - offsets are non-strictly monotonically increasing
+ *  - for a single offset there is at most one type marker
+ *  - for a single offset that has both a type marker and non-type markers, the
+ *    type marker appears before the others.
+ */
+static struct marker **add_marker(struct marker **mi,
+				  enum markertype type, unsigned int offset, char *ref)
+{
+	struct marker *nm;
+
+	while (*mi && (*mi)->offset < offset)
+		mi = &(*mi)->next;
+
+	if (*mi && (*mi)->offset == offset && is_type_marker((*mi)->type)) {
+		if (is_type_marker(type))
+			return mi;
+		mi = &(*mi)->next;
+	}
+
+	if (*mi && (*mi)->offset == offset && type == (*mi)->type)
+		return mi;
+
+	nm = xmalloc(sizeof(*nm));
+	nm->type = type;
+	nm->offset = offset;
+	nm->ref = ref;
+	nm->next = *mi;
+	*mi = nm;
+
+	return &nm->next;
+}
+
+void property_add_marker(struct property *prop,
+			 enum markertype type, unsigned int offset, char *ref)
+{
+	add_marker(&prop->val.markers, type, offset, ref);
+}
+
+static void add_string_markers(struct property *prop, unsigned int offset, int len)
+{
+	int l;
+	const char *p = prop->val.val + offset;
+	struct marker **mi = &prop->val.markers;
+
+	for (l = strlen(p) + 1; l < len; l += strlen(p + l) + 1)
+		mi = add_marker(mi, TYPE_STRING, offset + l, NULL);
+}
+
+void add_phandle_marker(struct dt_info *dti, struct property *prop, unsigned int offset)
+{
+	cell_t phandle;
+	struct node *refn;
+	char *ref;
+
+	if (prop->val.len < offset + 4) {
+		if (quiet < 1)
+			fprintf(stderr,
+				"Warning: property %s too short to contain a phandle at offset %u\n",
+				prop->name, offset);
+		return;
+	}
+
+	phandle = dtb_ld32(prop->val.val + offset);
+	refn = get_node_by_phandle(dti->dt, phandle);
+
+	if (!refn) {
+		if (quiet < 1)
+			fprintf(stderr,
+				"Warning: node referenced by phandle 0x%x in property %s not found\n",
+				phandle, prop->name);
+		return;
+	}
+
+	if (refn->labels)
+		ref = refn->labels->label;
+	else
+		ref = refn->fullpath;
+
+	add_marker(&prop->val.markers, REF_PHANDLE, offset, ref);
+}
+
+static enum markertype guess_value_type(struct property *prop, unsigned int offset, int len)
+{
+	const char *p = prop->val.val + offset;
+	int nnotstring = 0, nnul = 0;
+	int i;
+
+	for (i = 0; i < len; i++) {
+		if (! isstring(p[i]))
+			nnotstring++;
+		if (p[i] == '\0')
+			nnul++;
+	}
+
+	if ((p[len-1] == '\0') && (nnotstring == 0) && (nnul <= len - nnul)) {
+		if (nnul > 1)
+			add_string_markers(prop, offset, len);
+		return TYPE_STRING;
+	} else if ((len % sizeof(cell_t)) == 0) {
+		return TYPE_UINT32;
+	}
+
+	return TYPE_UINT8;
+}
+
+static void guess_type_markers(struct property *prop)
+{
+	struct marker **m = &prop->val.markers;
+	unsigned int offset = 0;
+
+	for (m = &prop->val.markers; *m; m = &((*m)->next)) {
+		if (is_type_marker((*m)->type))
+			/* assume the whole property is already marked */
+			return;
+
+		if ((*m)->offset > offset) {
+			m = add_marker(m, guess_value_type(prop, offset, (*m)->offset - offset),
+				       offset, NULL);
+
+			offset = (*m)->offset;
+		}
+
+		if ((*m)->type == REF_PHANDLE) {
+			m = add_marker(m, TYPE_UINT32, offset, NULL);
+			offset += 4;
+		}
+	}
+
+	if (offset < prop->val.len)
+		add_marker(m, guess_value_type(prop, offset, prop->val.len - offset),
+			   offset, NULL);
+}
+
+static void write_propval(FILE *f, struct property *prop)
+{
+	size_t len = prop->val.len;
+	struct marker *m;
+	enum markertype emit_type = TYPE_NONE;
+	char *srcstr;
+
+	if (len == 0) {
+		fprintf(f, ";");
+		if (annotate) {
+			srcstr = srcpos_string_first(prop->srcpos, annotate);
+			if (srcstr) {
+				fprintf(f, " /* %s */", srcstr);
+				free(srcstr);
+			}
+		}
+		fprintf(f, "\n");
+		return;
+	}
+
+	fprintf(f, " =");
+
+	guess_type_markers(prop);
+	m = prop->val.markers;
+
+	for_each_marker(m) {
+		size_t chunk_len = (m->next ? m->next->offset : len) - m->offset;
+		size_t data_len = type_marker_length(m) ? : len - m->offset;
+		const char *p = &prop->val.val[m->offset];
+		struct marker *m_phandle;
+
+		if (is_type_marker(m->type)) {
+			emit_type = m->type;
+			fprintf(f, " %s", delim_start[emit_type]);
+		} else if (m->type == LABEL)
+			fprintf(f, " %s:", m->ref);
+
+		if (emit_type == TYPE_NONE || chunk_len == 0)
+			continue;
+
+		switch(emit_type) {
+		case TYPE_UINT16:
+			write_propval_int(f, p, chunk_len, 2);
+			break;
+		case TYPE_UINT32:
+			m_phandle = prop->val.markers;
+			for_each_marker_of_type(m_phandle, REF_PHANDLE)
+				if (m->offset == m_phandle->offset)
+					break;
+
+			if (m_phandle) {
+				if (m_phandle->ref[0] == '/')
+					fprintf(f, "&{%s}", m_phandle->ref);
+				else
+					fprintf(f, "&%s", m_phandle->ref);
+				if (chunk_len > 4) {
+					fputc(' ', f);
+					write_propval_int(f, p + 4, chunk_len - 4, 4);
+				}
+			} else {
+				write_propval_int(f, p, chunk_len, 4);
+			}
+			if (data_len > chunk_len)
+				fputc(' ', f);
+			break;
+		case TYPE_UINT64:
+			write_propval_int(f, p, chunk_len, 8);
+			break;
+		case TYPE_STRING:
+			write_propval_string(f, p, chunk_len);
+			break;
+		default:
+			write_propval_int(f, p, chunk_len, 1);
+		}
+
+		if (chunk_len == data_len) {
+			size_t pos = m->offset + chunk_len;
+			fprintf(f, pos == len ? "%s" : "%s,",
+			        delim_end[emit_type] ? : "");
+			emit_type = TYPE_NONE;
+		}
+	}
+	fprintf(f, ";");
+	if (annotate) {
+		srcstr = srcpos_string_first(prop->srcpos, annotate);
+		if (srcstr) {
+			fprintf(f, " /* %s */", srcstr);
+			free(srcstr);
+		}
+	}
+	fprintf(f, "\n");
+}
+
+static void write_tree_source_node(FILE *f, struct node *tree, int level)
+{
+	struct property *prop;
+	struct node *child;
+	struct label *l;
+	char *srcstr;
+
+	write_prefix(f, level);
+	for_each_label(tree->labels, l)
+		fprintf(f, "%s: ", l->label);
+	if (tree->name && (*tree->name))
+		fprintf(f, "%s {", tree->name);
+	else
+		fprintf(f, "/ {");
+
+	if (annotate) {
+		srcstr = srcpos_string_first(tree->srcpos, annotate);
+		if (srcstr) {
+			fprintf(f, " /* %s */", srcstr);
+			free(srcstr);
+		}
+	}
+	fprintf(f, "\n");
+
+	for_each_property(tree, prop) {
+		write_prefix(f, level+1);
+		for_each_label(prop->labels, l)
+			fprintf(f, "%s: ", l->label);
+		fprintf(f, "%s", prop->name);
+		write_propval(f, prop);
+	}
+	for_each_child(tree, child) {
+		fprintf(f, "\n");
+		write_tree_source_node(f, child, level+1);
+	}
+	write_prefix(f, level);
+	fprintf(f, "};");
+	if (annotate) {
+		srcstr = srcpos_string_last(tree->srcpos, annotate);
+		if (srcstr) {
+			fprintf(f, " /* %s */", srcstr);
+			free(srcstr);
+		}
+	}
+	fprintf(f, "\n");
+}
+
+void dt_to_source(FILE *f, struct dt_info *dti)
+{
+	struct reserve_info *re;
+
+	fprintf(f, "/dts-v1/;\n");
+	if (dti->dtsflags & DTSF_PLUGIN)
+		fprintf(f, "/plugin/;\n");
+	fprintf(f, "\n");
+
+	for (re = dti->reservelist; re; re = re->next) {
+		struct label *l;
+
+		for_each_label(re->labels, l)
+			fprintf(f, "%s: ", l->label);
+		fprintf(f, "/memreserve/\t0x%016llx 0x%016llx;\n",
+			(unsigned long long)re->address,
+			(unsigned long long)re->size);
+	}
+
+	write_tree_source_node(f, dti->dt, 0);
+}