objtool: Add .call_sites section

In preparation for call depth tracking provide a section which collects all
direct calls.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111146.016511961@infradead.org

arch/x86/kernel/vmlinux.lds.S

@@ -291,6 +291,13 @@ SECTIONS
 		*(.return_sites)
 		__return_sites_end = .;
 	}
+
+	. = ALIGN(8);
+	.call_sites : AT(ADDR(.call_sites) - LOAD_OFFSET) {
+		__call_sites = .;
+		*(.call_sites)
+		__call_sites_end = .;
+	}
 #endif
 
 #ifdef CONFIG_X86_KERNEL_IBT

tools/objtool/check.c

@@ -902,6 +902,49 @@ static int create_mcount_loc_sections(struct objtool_file *file)
 	return 0;
 }
 
+static int create_direct_call_sections(struct objtool_file *file)
+{
+	struct instruction *insn;
+	struct section *sec;
+	unsigned int *loc;
+	int idx;
+
+	sec = find_section_by_name(file->elf, ".call_sites");
+	if (sec) {
+		INIT_LIST_HEAD(&file->call_list);
+		WARN("file already has .call_sites section, skipping");
+		return 0;
+	}
+
+	if (list_empty(&file->call_list))
+		return 0;
+
+	idx = 0;
+	list_for_each_entry(insn, &file->call_list, call_node)
+		idx++;
+
+	sec = elf_create_section(file->elf, ".call_sites", 0, sizeof(unsigned int), idx);
+	if (!sec)
+		return -1;
+
+	idx = 0;
+	list_for_each_entry(insn, &file->call_list, call_node) {
+
+		loc = (unsigned int *)sec->data->d_buf + idx;
+		memset(loc, 0, sizeof(unsigned int));
+
+		if (elf_add_reloc_to_insn(file->elf, sec,
+					  idx * sizeof(unsigned int),
+					  R_X86_64_PC32,
+					  insn->sec, insn->offset))
+			return -1;
+
+		idx++;
+	}
+
+	return 0;
+}
+
 /*
  * Warnings shouldn't be reported for ignored functions.
  */
@@ -1279,6 +1322,9 @@ static void annotate_call_site(struct objtool_file *file,
 		return;
 	}
 
+	if (insn->type == INSN_CALL && !insn->sec->init)
+		list_add_tail(&insn->call_node, &file->call_list);
+
 	if (!sibling && dead_end_function(file, sym))
 		insn->dead_end = true;
 }
@@ -4305,6 +4351,11 @@ int check(struct objtool_file *file)
 		if (ret < 0)
 			goto out;
 		warnings += ret;
+
+		ret = create_direct_call_sections(file);
+		if (ret < 0)
+			goto out;
+		warnings += ret;
 	}
 
 	if (opts.mcount) {

tools/objtool/include/objtool/objtool.h

@@ -28,6 +28,7 @@ struct objtool_file {
 	struct list_head static_call_list;
 	struct list_head mcount_loc_list;
 	struct list_head endbr_list;
+	struct list_head call_list;
 	bool ignore_unreachables, hints, rodata;
 
 	unsigned int nr_endbr;

tools/objtool/objtool.c

@@ -106,6 +106,7 @@ struct objtool_file *objtool_open_read(const char *_objname)
 	INIT_LIST_HEAD(&file.static_call_list);
 	INIT_LIST_HEAD(&file.mcount_loc_list);
 	INIT_LIST_HEAD(&file.endbr_list);
+	INIT_LIST_HEAD(&file.call_list);
 	file.ignore_unreachables = opts.no_unreachable;
 	file.hints = false;