Commit 4855022a authored Jul 07, 2017 by Josh Poimboeuf Committed by Ingo Molnar Jul 08, 2017

objtool: Fix sibling call detection logic

With some configs, objtool reports the following warning:

arch/x86/kernel/ftrace.o: warning: objtool: ftrace_modify_code_direct()+0x2d: sibling call from callable instruction with modified stack frame

The instruction it's complaining about isn't actually a sibling call.
It's just a normal jump to an address inside the function. Objtool
thought it was a sibling call because the instruction's jump_dest wasn't
initialized because the function was supposed to be ignored due to its
use of sync_core().

Objtool ended up validating the function instead of ignoring it because
it didn't properly recognize a sibling call to the function. So fix the
sibling call logic. Also add a warning to catch ignored functions being
validated so we'll get a more useful error message next time.

Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/96cc8ecbcdd8cb29ddd783817b4af918a6a171b0.1499437107.git.jpoimboe@redhat.com

Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 4422d80e

tools/objtool/check.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -1371,6 +1371,12 @@ static int validate_branch(struct objtool_file file, struct instruction first,

		func = insn->func;

		if (func && insn->ignore) {
		WARN_FUNC("BUG: why am I validating an ignored function?",
		sec, insn->offset);
		return -1;
		}

		if (insn->visited) {
		if (!!insn_state_match(insn, &state))
		return 1;
		@@ -1426,16 +1432,19 @@ static int validate_branch(struct objtool_file file, struct instruction first,

		case INSN_JUMP_CONDITIONAL:
		case INSN_JUMP_UNCONDITIONAL:
		if (insn->jump_dest) {
		if (insn->jump_dest &&
		(!func \|\| !insn->jump_dest->func \|\|
		func == insn->jump_dest->func)) {
		ret = validate_branch(file, insn->jump_dest,
		state);
		if (ret)
		return 1;

		} else if (func && has_modified_stack_frame(&state)) {
		WARN_FUNC("sibling call from callable instruction with modified stack frame",
		sec, insn->offset);
		return 1;
		} /* else it's a sibling call */
		}

		if (insn->type == INSN_JUMP_UNCONDITIONAL)
		return 0;