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, 645 insertions, 0 deletions

diff --git a/tools/perf/util/libbfd.c b/tools/perf/util/libbfd.c
new file mode 100644
index 000000000..c1c12308c
--- /dev/null
+++ b/tools/perf/util/libbfd.c
@@ -0,0 +1,645 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "libbfd.h"
+#include "annotate.h"
+#include "bpf-event.h"
+#include "bpf-utils.h"
+#include "debug.h"
+#include "dso.h"
+#include "env.h"
+#include "map.h"
+#include "srcline.h"
+#include "symbol.h"
+#include "symbol_conf.h"
+#include "util.h"
+#include <tools/dis-asm-compat.h>
+#ifdef HAVE_LIBBPF_SUPPORT
+#include <bpf/bpf.h>
+#include <bpf/btf.h>
+#endif
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#define PACKAGE "perf"
+#include <bfd.h>
+
+/*
+ * Implement addr2line using libbfd.
+ */
+struct a2l_data {
+	const char *input;
+	u64 addr;
+
+	bool found;
+	const char *filename;
+	const char *funcname;
+	unsigned int line;
+
+	bfd *abfd;
+	asymbol **syms;
+};
+
+static bool perf_bfd_lock(void *bfd_mutex)
+{
+	mutex_lock(bfd_mutex);
+	return true;
+}
+
+static bool perf_bfd_unlock(void *bfd_mutex)
+{
+	mutex_unlock(bfd_mutex);
+	return true;
+}
+
+static void perf_bfd_init(void)
+{
+	static struct mutex bfd_mutex;
+
+	mutex_init_recursive(&bfd_mutex);
+
+	if (bfd_init() != BFD_INIT_MAGIC) {
+		pr_err("Error initializing libbfd\n");
+		return;
+	}
+	if (!bfd_thread_init(perf_bfd_lock, perf_bfd_unlock, &bfd_mutex))
+		pr_err("Error initializing libbfd threading\n");
+}
+
+static void ensure_bfd_init(void)
+{
+	static pthread_once_t bfd_init_once = PTHREAD_ONCE_INIT;
+
+	pthread_once(&bfd_init_once, perf_bfd_init);
+}
+
+static int bfd_error(const char *string)
+{
+	const char *errmsg;
+
+	errmsg = bfd_errmsg(bfd_get_error());
+	fflush(stdout);
+
+	if (string)
+		pr_debug("%s: %s\n", string, errmsg);
+	else
+		pr_debug("%s\n", errmsg);
+
+	return -1;
+}
+
+static int slurp_symtab(bfd *abfd, struct a2l_data *a2l)
+{
+	long storage;
+	long symcount;
+	asymbol **syms;
+	bfd_boolean dynamic = FALSE;
+
+	if ((bfd_get_file_flags(abfd) & HAS_SYMS) == 0)
+		return bfd_error(bfd_get_filename(abfd));
+
+	storage = bfd_get_symtab_upper_bound(abfd);
+	if (storage == 0L) {
+		storage = bfd_get_dynamic_symtab_upper_bound(abfd);
+		dynamic = TRUE;
+	}
+	if (storage < 0L)
+		return bfd_error(bfd_get_filename(abfd));
+
+	syms = malloc(storage);
+	if (dynamic)
+		symcount = bfd_canonicalize_dynamic_symtab(abfd, syms);
+	else
+		symcount = bfd_canonicalize_symtab(abfd, syms);
+
+	if (symcount < 0) {
+		free(syms);
+		return bfd_error(bfd_get_filename(abfd));
+	}
+
+	a2l->syms = syms;
+	return 0;
+}
+
+static void find_address_in_section(bfd *abfd, asection *section, void *data)
+{
+	bfd_vma pc, vma;
+	bfd_size_type size;
+	struct a2l_data *a2l = data;
+	flagword flags;
+
+	if (a2l->found)
+		return;
+
+#ifdef bfd_get_section_flags
+	flags = bfd_get_section_flags(abfd, section);
+#else
+	flags = bfd_section_flags(section);
+#endif
+	if ((flags & SEC_ALLOC) == 0)
+		return;
+
+	pc = a2l->addr;
+#ifdef bfd_get_section_vma
+	vma = bfd_get_section_vma(abfd, section);
+#else
+	vma = bfd_section_vma(section);
+#endif
+#ifdef bfd_get_section_size
+	size = bfd_get_section_size(section);
+#else
+	size = bfd_section_size(section);
+#endif
+
+	if (pc < vma || pc >= vma + size)
+		return;
+
+	a2l->found = bfd_find_nearest_line(abfd, section, a2l->syms, pc - vma,
+					   &a2l->filename, &a2l->funcname,
+					   &a2l->line);
+
+	if (a2l->filename && !strlen(a2l->filename))
+		a2l->filename = NULL;
+}
+
+static struct a2l_data *addr2line_init(const char *path)
+{
+	bfd *abfd;
+	struct a2l_data *a2l = NULL;
+
+	ensure_bfd_init();
+	abfd = bfd_openr(path, NULL);
+	if (abfd == NULL)
+		return NULL;
+
+	if (!bfd_check_format(abfd, bfd_object))
+		goto out;
+
+	a2l = zalloc(sizeof(*a2l));
+	if (a2l == NULL)
+		goto out;
+
+	a2l->abfd = abfd;
+	a2l->input = strdup(path);
+	if (a2l->input == NULL)
+		goto out;
+
+	if (slurp_symtab(abfd, a2l))
+		goto out;
+
+	return a2l;
+
+out:
+	if (a2l) {
+		zfree((char **)&a2l->input);
+		free(a2l);
+	}
+	bfd_close(abfd);
+	return NULL;
+}
+
+static void addr2line_cleanup(struct a2l_data *a2l)
+{
+	if (a2l->abfd)
+		bfd_close(a2l->abfd);
+	zfree((char **)&a2l->input);
+	zfree(&a2l->syms);
+	free(a2l);
+}
+
+static int inline_list__append_dso_a2l(struct dso *dso,
+				       struct inline_node *node,
+				       struct symbol *sym)
+{
+	struct a2l_data *a2l = dso__a2l(dso);
+	struct symbol *inline_sym = new_inline_sym(dso, sym, a2l->funcname);
+	char *srcline = NULL;
+
+	if (a2l->filename)
+		srcline = srcline_from_fileline(a2l->filename, a2l->line);
+
+	return inline_list__append(inline_sym, srcline, node);
+}
+
+int libbfd__addr2line(const char *dso_name, u64 addr,
+		      char **file, unsigned int *line, struct dso *dso,
+		      bool unwind_inlines, struct inline_node *node,
+		      struct symbol *sym)
+{
+	int ret = 0;
+	struct a2l_data *a2l = dso__a2l(dso);
+
+	if (!a2l) {
+		a2l = addr2line_init(dso_name);
+		dso__set_a2l(dso, a2l);
+	}
+
+	if (a2l == NULL) {
+		if (!symbol_conf.addr2line_disable_warn)
+			pr_warning("addr2line_init failed for %s\n", dso_name);
+		return 0;
+	}
+
+	a2l->addr = addr;
+	a2l->found = false;
+
+	bfd_map_over_sections(a2l->abfd, find_address_in_section, a2l);
+
+	if (!a2l->found)
+		return 0;
+
+	if (unwind_inlines) {
+		int cnt = 0;
+
+		if (node && inline_list__append_dso_a2l(dso, node, sym))
+			return 0;
+
+		while (bfd_find_inliner_info(a2l->abfd, &a2l->filename,
+					     &a2l->funcname, &a2l->line) &&
+		       cnt++ < MAX_INLINE_NEST) {
+
+			if (a2l->filename && !strlen(a2l->filename))
+				a2l->filename = NULL;
+
+			if (node != NULL) {
+				if (inline_list__append_dso_a2l(dso, node, sym))
+					return 0;
+				// found at least one inline frame
+				ret = 1;
+			}
+		}
+	}
+
+	if (file) {
+		*file = a2l->filename ? strdup(a2l->filename) : NULL;
+		ret = *file ? 1 : 0;
+	}
+
+	if (line)
+		*line = a2l->line;
+
+	return ret;
+}
+
+void dso__free_a2l_libbfd(struct dso *dso)
+{
+	struct a2l_data *a2l = dso__a2l(dso);
+
+	if (!a2l)
+		return;
+
+	addr2line_cleanup(a2l);
+
+	dso__set_a2l(dso, NULL);
+}
+
+static int bfd_symbols__cmpvalue(const void *a, const void *b)
+{
+	const asymbol *as = *(const asymbol **)a, *bs = *(const asymbol **)b;
+
+	if (bfd_asymbol_value(as) != bfd_asymbol_value(bs))
+		return bfd_asymbol_value(as) - bfd_asymbol_value(bs);
+
+	return bfd_asymbol_name(as)[0] - bfd_asymbol_name(bs)[0];
+}
+
+static int bfd2elf_binding(asymbol *symbol)
+{
+	if (symbol->flags & BSF_WEAK)
+		return STB_WEAK;
+	if (symbol->flags & BSF_GLOBAL)
+		return STB_GLOBAL;
+	if (symbol->flags & BSF_LOCAL)
+		return STB_LOCAL;
+	return -1;
+}
+
+int dso__load_bfd_symbols(struct dso *dso, const char *debugfile)
+{
+	int err = -1;
+	long symbols_size, symbols_count, i;
+	asection *section;
+	asymbol **symbols, *sym;
+	struct symbol *symbol;
+	bfd *abfd;
+	u64 start, len;
+
+	ensure_bfd_init();
+	abfd = bfd_openr(debugfile, NULL);
+	if (!abfd)
+		return -1;
+
+	if (!bfd_check_format(abfd, bfd_object)) {
+		pr_debug2("%s: cannot read %s bfd file.\n", __func__,
+			  dso__long_name(dso));
+		goto out_close;
+	}
+
+	if (bfd_get_flavour(abfd) == bfd_target_elf_flavour)
+		goto out_close;
+
+	symbols_size = bfd_get_symtab_upper_bound(abfd);
+	if (symbols_size == 0) {
+		bfd_close(abfd);
+		return 0;
+	}
+
+	if (symbols_size < 0)
+		goto out_close;
+
+	symbols = malloc(symbols_size);
+	if (!symbols)
+		goto out_close;
+
+	symbols_count = bfd_canonicalize_symtab(abfd, symbols);
+	if (symbols_count < 0)
+		goto out_free;
+
+	section = bfd_get_section_by_name(abfd, ".text");
+	if (section) {
+		for (i = 0; i < symbols_count; ++i) {
+			if (!strcmp(bfd_asymbol_name(symbols[i]), "__ImageBase") ||
+			    !strcmp(bfd_asymbol_name(symbols[i]), "__image_base__"))
+				break;
+		}
+		if (i < symbols_count) {
+			/* PE symbols can only have 4 bytes, so use .text high bits */
+			u64 text_offset = (section->vma - (u32)section->vma)
+				+ (u32)bfd_asymbol_value(symbols[i]);
+			dso__set_text_offset(dso, text_offset);
+			dso__set_text_end(dso, (section->vma - text_offset) + section->size);
+		} else {
+			dso__set_text_offset(dso, section->vma - section->filepos);
+			dso__set_text_end(dso, section->filepos + section->size);
+		}
+	}
+
+	qsort(symbols, symbols_count, sizeof(asymbol *), bfd_symbols__cmpvalue);
+
+#ifdef bfd_get_section
+#define bfd_asymbol_section bfd_get_section
+#endif
+	for (i = 0; i < symbols_count; ++i) {
+		sym = symbols[i];
+		section = bfd_asymbol_section(sym);
+		if (bfd2elf_binding(sym) < 0)
+			continue;
+
+		while (i + 1 < symbols_count &&
+		       bfd_asymbol_section(symbols[i + 1]) == section &&
+		       bfd2elf_binding(symbols[i + 1]) < 0)
+			i++;
+
+		if (i + 1 < symbols_count &&
+		    bfd_asymbol_section(symbols[i + 1]) == section)
+			len = symbols[i + 1]->value - sym->value;
+		else
+			len = section->size - sym->value;
+
+		start = bfd_asymbol_value(sym) - dso__text_offset(dso);
+		symbol = symbol__new(start, len, bfd2elf_binding(sym), STT_FUNC,
+				     bfd_asymbol_name(sym));
+		if (!symbol)
+			goto out_free;
+
+		symbols__insert(dso__symbols(dso), symbol);
+	}
+#ifdef bfd_get_section
+#undef bfd_asymbol_section
+#endif
+
+	symbols__fixup_end(dso__symbols(dso), false);
+	symbols__fixup_duplicate(dso__symbols(dso));
+	dso__set_adjust_symbols(dso, true);
+
+	err = 0;
+out_free:
+	free(symbols);
+out_close:
+	bfd_close(abfd);
+	return err;
+}
+
+int libbfd__read_build_id(const char *filename, struct build_id *bid)
+{
+	size_t size = sizeof(bid->data);
+	int err = -1, fd;
+	bfd *abfd;
+
+	if (!filename)
+		return -EFAULT;
+
+	errno = 0;
+	if (!is_regular_file(filename))
+		return errno == 0 ? -EWOULDBLOCK : -errno;
+
+	fd = open(filename, O_RDONLY);
+	if (fd < 0)
+		return -1;
+
+	ensure_bfd_init();
+	abfd = bfd_fdopenr(filename, /*target=*/NULL, fd);
+	if (!abfd)
+		return -1;
+
+	if (!bfd_check_format(abfd, bfd_object)) {
+		pr_debug2("%s: cannot read %s bfd file.\n", __func__, filename);
+		goto out_close;
+	}
+
+	if (!abfd->build_id || abfd->build_id->size > size)
+		goto out_close;
+
+	memcpy(bid->data, abfd->build_id->data, abfd->build_id->size);
+	memset(bid->data + abfd->build_id->size, 0, size - abfd->build_id->size);
+	err = bid->size = abfd->build_id->size;
+
+out_close:
+	bfd_close(abfd);
+	return err;
+}
+
+int libbfd_filename__read_debuglink(const char *filename, char *debuglink,
+				    size_t size)
+{
+	int err = -1;
+	asection *section;
+	bfd *abfd;
+
+	ensure_bfd_init();
+	abfd = bfd_openr(filename, NULL);
+	if (!abfd)
+		return -1;
+
+	if (!bfd_check_format(abfd, bfd_object)) {
+		pr_debug2("%s: cannot read %s bfd file.\n", __func__, filename);
+		goto out_close;
+	}
+
+	section = bfd_get_section_by_name(abfd, ".gnu_debuglink");
+	if (!section)
+		goto out_close;
+
+	if (section->size > size)
+		goto out_close;
+
+	if (!bfd_get_section_contents(abfd, section, debuglink, 0,
+				      section->size))
+		goto out_close;
+
+	err = 0;
+
+out_close:
+	bfd_close(abfd);
+	return err;
+}
+
+int symbol__disassemble_bpf_libbfd(struct symbol *sym __maybe_unused,
+				   struct annotate_args *args  __maybe_unused)
+{
+#ifdef HAVE_LIBBPF_SUPPORT
+	struct annotation *notes = symbol__annotation(sym);
+	struct bpf_prog_linfo *prog_linfo = NULL;
+	struct bpf_prog_info_node *info_node;
+	int len = sym->end - sym->start;
+	disassembler_ftype disassemble;
+	struct map *map = args->ms->map;
+	struct perf_bpil *info_linear;
+	struct disassemble_info info;
+	struct dso *dso = map__dso(map);
+	int pc = 0, count, sub_id;
+	struct btf *btf = NULL;
+	char tpath[PATH_MAX];
+	size_t buf_size;
+	int nr_skip = 0;
+	char *buf;
+	bfd *bfdf;
+	int ret;
+	FILE *s;
+
+	if (dso__binary_type(dso) != DSO_BINARY_TYPE__BPF_PROG_INFO)
+		return SYMBOL_ANNOTATE_ERRNO__BPF_INVALID_FILE;
+
+	pr_debug("%s: handling sym %s addr %" PRIx64 " len %" PRIx64 "\n", __func__,
+		  sym->name, sym->start, sym->end - sym->start);
+
+	memset(tpath, 0, sizeof(tpath));
+	perf_exe(tpath, sizeof(tpath));
+
+	ensure_bfd_init();
+	bfdf = bfd_openr(tpath, NULL);
+	if (bfdf == NULL)
+		abort();
+
+	if (!bfd_check_format(bfdf, bfd_object))
+		abort();
+
+	s = open_memstream(&buf, &buf_size);
+	if (!s) {
+		ret = errno;
+		goto out;
+	}
+	init_disassemble_info_compat(&info, s,
+				     (fprintf_ftype) fprintf,
+				     fprintf_styled);
+	info.arch = bfd_get_arch(bfdf);
+	info.mach = bfd_get_mach(bfdf);
+
+	info_node = perf_env__find_bpf_prog_info(dso__bpf_prog(dso)->env,
+						 dso__bpf_prog(dso)->id);
+	if (!info_node) {
+		ret = SYMBOL_ANNOTATE_ERRNO__BPF_MISSING_BTF;
+		goto out;
+	}
+	info_linear = info_node->info_linear;
+	sub_id = dso__bpf_prog(dso)->sub_id;
+
+	info.buffer = (void *)(uintptr_t)(info_linear->info.jited_prog_insns);
+	info.buffer_length = info_linear->info.jited_prog_len;
+
+	if (info_linear->info.nr_line_info)
+		prog_linfo = bpf_prog_linfo__new(&info_linear->info);
+
+	if (info_linear->info.btf_id) {
+		struct btf_node *node;
+
+		node = perf_env__find_btf(dso__bpf_prog(dso)->env,
+					  info_linear->info.btf_id);
+		if (node)
+			btf = btf__new((__u8 *)(node->data),
+				       node->data_size);
+	}
+
+	disassemble_init_for_target(&info);
+
+#ifdef DISASM_FOUR_ARGS_SIGNATURE
+	disassemble = disassembler(info.arch,
+				   bfd_big_endian(bfdf),
+				   info.mach,
+				   bfdf);
+#else
+	disassemble = disassembler(bfdf);
+#endif
+	if (disassemble == NULL)
+		abort();
+
+	fflush(s);
+	do {
+		const struct bpf_line_info *linfo = NULL;
+		struct disasm_line *dl;
+		size_t prev_buf_size;
+		const char *srcline;
+		u64 addr;
+
+		addr = pc + ((u64 *)(uintptr_t)(info_linear->info.jited_ksyms))[sub_id];
+		count = disassemble(pc, &info);
+
+		if (prog_linfo)
+			linfo = bpf_prog_linfo__lfind_addr_func(prog_linfo,
+								addr, sub_id,
+								nr_skip);
+
+		if (linfo && btf) {
+			srcline = btf__name_by_offset(btf, linfo->line_off);
+			nr_skip++;
+		} else
+			srcline = NULL;
+
+		fprintf(s, "\n");
+		prev_buf_size = buf_size;
+		fflush(s);
+
+		if (!annotate_opts.hide_src_code && srcline) {
+			args->offset = -1;
+			args->line = strdup(srcline);
+			args->line_nr = 0;
+			args->fileloc = NULL;
+			args->ms->sym = sym;
+			dl = disasm_line__new(args);
+			if (dl) {
+				annotation_line__add(&dl->al,
+						     &notes->src->source);
+			}
+		}
+
+		args->offset = pc;
+		args->line = buf + prev_buf_size;
+		args->line_nr = 0;
+		args->fileloc = NULL;
+		args->ms->sym = sym;
+		dl = disasm_line__new(args);
+		if (dl)
+			annotation_line__add(&dl->al, &notes->src->source);
+
+		pc += count;
+	} while (count > 0 && pc < len);
+
+	ret = 0;
+out:
+	free(prog_linfo);
+	btf__free(btf);
+	fclose(s);
+	bfd_close(bfdf);
+	return ret;
+#else
+	return SYMBOL_ANNOTATE_ERRNO__NO_LIBOPCODES_FOR_BPF;
+#endif
+}