Commit 5a9c361a authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

objtool: Allow STT_NOTYPE -> STT_FUNC+0 sibling-calls 



Teach objtool about STT_NOTYPE -> STT_FUNC+0 sibling calls. Doing do
allows slightly simpler .S files.

There is a slight complication in that we specifically do not want to
allow sibling calls from symbol holes (previously covered by STT_WEAK
symbols) -- such things exist where a weak function has a .cold
subfunction for example.

Additionally, STT_NOTYPE tail-calls are allowed to happen with a
modified stack frame, they don't need to obey the normal rules after
all.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
parent dbcdbdfd

tools/objtool/check.c

+47 −27
Original line number Diff line number Diff line
@@ -129,16 +129,13 @@ static bool is_jump_table_jump(struct instruction *insn) 
static bool is_sibling_call(struct instruction *insn)

{

	/*

	 * Assume only ELF functions can make sibling calls.  This ensures

	 * sibling call detection consistency between vmlinux.o and individual

	 * objects.

	 * Assume only STT_FUNC calls have jump-tables.

	 */

	if (!insn_func(insn))

		return false;



	if (insn_func(insn)) {

		/* An indirect jump is either a sibling call or a jump to a table. */

		if (insn->type == INSN_JUMP_DYNAMIC)

			return !is_jump_table_jump(insn);

	}



	/* add_jump_destinations() sets insn->call_dest for sibling calls. */

	return (is_static_jump(insn) && insn->call_dest);
@@ -1400,27 +1397,50 @@ static void add_return_call(struct objtool_file *file, struct instruction *insn, 
		list_add_tail(&insn->call_node, &file->return_thunk_list);

}



static bool same_function(struct instruction *insn1, struct instruction *insn2)

{

	return insn_func(insn1)->pfunc == insn_func(insn2)->pfunc;

}



static bool is_first_func_insn(struct objtool_file *file, struct instruction *insn)

static bool is_first_func_insn(struct objtool_file *file,

			       struct instruction *insn, struct symbol *sym)

{

	if (insn->offset == insn_func(insn)->offset)

	if (insn->offset == sym->offset)

		return true;



	/* Allow direct CALL/JMP past ENDBR */

	if (opts.ibt) {

		struct instruction *prev = prev_insn_same_sym(file, insn);



		if (prev && prev->type == INSN_ENDBR &&

		    insn->offset == insn_func(insn)->offset + prev->len)

		    insn->offset == sym->offset + prev->len)

			return true;

	}



	return false;

}



/*

 * A sibling call is a tail-call to another symbol -- to differentiate from a

 * recursive tail-call which is to the same symbol.

 */

static bool jump_is_sibling_call(struct objtool_file *file,

				 struct instruction *from, struct instruction *to)

{

	struct symbol *fs = from->sym;

	struct symbol *ts = to->sym;



	/* Not a sibling call if from/to a symbol hole */

	if (!fs || !ts)

		return false;



	/* Not a sibling call if not targeting the start of a symbol. */

	if (!is_first_func_insn(file, to, ts))

		return false;



	/* Disallow sibling calls into STT_NOTYPE */

	if (ts->type == STT_NOTYPE)

		return false;



	/* Must not be self to be a sibling */

	return fs->pfunc != ts->pfunc;

}



/*

 * Find the destination instructions for all jumps.

 */
@@ -1519,9 +1539,10 @@ static int add_jump_destinations(struct objtool_file *file) 
			    strstr(insn_func(jump_dest)->name, ".cold")) {

				insn_func(insn)->cfunc = insn_func(jump_dest);

				insn_func(jump_dest)->pfunc = insn_func(insn);

			}

		}



			} else if (!same_function(insn, jump_dest) &&

				   is_first_func_insn(file, jump_dest)) {

		if (jump_is_sibling_call(file, insn, jump_dest)) {

			/*

			 * Internal sibling call without reloc or with

			 * STT_SECTION reloc.
@@ -1529,7 +1550,6 @@ static int add_jump_destinations(struct objtool_file *file) 
			add_call_dest(file, insn, insn_func(jump_dest), true);

			continue;

		}

		}



		insn->jump_dest = jump_dest;

	}
@@ -3309,7 +3329,7 @@ static int validate_sibling_call(struct objtool_file *file, 
				 struct instruction *insn,

				 struct insn_state *state)

{

	if (has_modified_stack_frame(insn, state)) {

	if (insn_func(insn) && has_modified_stack_frame(insn, state)) {

		WARN_FUNC("sibling call from callable instruction with modified stack frame",

				insn->sec, insn->offset);

		return 1;