[PATCH 3/7] objtool: Add support for intra-function calls

[Alexandre Chartre]

Change objtool to support intra-function calls. An intra-function call
is represented in objtool as a push onto the stack (of the return
address), and a jump to the destination address. That way the stack
information is correctly updated and the call flow is still accurate.

Signed-off-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
---
 tools/objtool/check.c | 73 ++++++++++++++++++++++++++++++++++++++++++-
 tools/objtool/check.h |  1 +
 2 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 214809ac2776..0cec91291d46 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -657,6 +657,18 @@ static int add_call_destinations(struct objtool_file *file)
 		if (insn->type != INSN_CALL)
 			continue;
 
+		if (insn->intra_function_call) {
+			dest_off = insn->offset + insn->len + insn->immediate;
+			insn->jump_dest = find_insn(file, insn->sec, dest_off);
+			if (insn->jump_dest)
+				continue;
+
+			WARN_FUNC("can't find call dest at %s+0x%lx",
+				  insn->sec, insn->offset,
+				  insn->sec->name, dest_off);
+			return -1;
+		}
+
 		rela = find_rela_by_dest_range(insn->sec, insn->offset,
 					       insn->len);
 		if (!rela) {
@@ -1289,6 +1301,49 @@ static int read_retpoline_hints(struct objtool_file *file)
 	return 0;
 }
 
+static int read_intra_function_call(struct objtool_file *file)
+{
+	struct section *sec;
+	struct instruction *insn;
+	struct rela *rela;
+
+	sec = find_section_by_name(file->elf,
+				   ".rela.discard.intra_function_call");
+	if (!sec)
+		return 0;
+
+	list_for_each_entry(rela, &sec->rela_list, list) {
+		if (rela->sym->type != STT_SECTION) {
+			WARN("unexpected relocation symbol type in %s",
+			     sec->name);
+			return -1;
+		}
+
+		insn = find_insn(file, rela->sym->sec, rela->addend);
+		if (!insn) {
+			WARN("bad .discard.intra_function_call entry");
+			return -1;
+		}
+
+		if (insn->type != INSN_CALL) {
+			WARN_FUNC("intra_function_call not a call",
+				  insn->sec, insn->offset);
+			return -1;
+		}
+
+		insn->intra_function_call = true;
+		/*
+		 * For the impact on the stack, make an intra-function
+		 * call behaves like a push of an immediate value (the
+		 * return address).
+		 */
+		insn->stack_op.src.type = OP_SRC_CONST;
+		insn->stack_op.dest.type = OP_DEST_PUSH;
+	}
+
+	return 0;
+}
+
 static void mark_rodata(struct objtool_file *file)
 {
 	struct section *sec;
@@ -1344,6 +1399,10 @@ static int decode_sections(struct objtool_file *file)
 	if (ret)
 		return ret;
 
+	ret = read_intra_function_call(file);
+	if (ret)
+		return ret;
+
 	ret = add_call_destinations(file);
 	if (ret)
 		return ret;
@@ -2092,7 +2151,8 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 				return ret;
 
 			if (!no_fp && func && !is_fentry_call(insn) &&
-			    !has_valid_stack_frame(&state)) {
+			    !has_valid_stack_frame(&state) &&
+			    !insn->intra_function_call) {
 				WARN_FUNC("call without frame pointer save/setup",
 					  sec, insn->offset);
 				return 1;
@@ -2101,6 +2161,17 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 			if (dead_end_function(file, insn->call_dest))
 				return 0;
 
+			if (insn->intra_function_call) {
+				update_insn_state(insn, &state);
+				ret = validate_branch(file, func, insn,
+						      insn->jump_dest, state);
+				if (ret) {
+					if (backtrace)
+						BT_FUNC("(intra-call)", insn);
+					return ret;
+				}
+			}
+
 			break;
 
 		case INSN_JUMP_CONDITIONAL:
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index cffb23d81782..2bd6d2f46baa 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -35,6 +35,7 @@ struct instruction {
 	unsigned long immediate;
 	unsigned int alt_group;
 	bool dead_end, ignore, hint, save, restore, ignore_alts;
+	bool intra_function_call;
 	bool retpoline_safe;
 	u8 visited;
 	struct symbol *call_dest;
-- 
2.18.2