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Commit b68b9907 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Thomas Gleixner
Browse files

objtool: Support conditional retpolines 



A Clang-built kernel is showing the following warning:

  arch/x86/kernel/platform-quirks.o: warning: objtool: x86_early_init_platform_quirks()+0x84: unreachable instruction

That corresponds to this code:

  7e:   0f 85 00 00 00 00       jne    84 <x86_early_init_platform_quirks+0x84>
                        80: R_X86_64_PC32       __x86_indirect_thunk_r11-0x4
  84:   c3                      retq

This is a conditional retpoline sibling call, which is now possible
thanks to retpolines.  Objtool hasn't seen that before.  It's
incorrectly interpreting the conditional jump as an unconditional
dynamic jump.

Reported-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/30d4c758b267ef487fb97e6ecb2f148ad007b554.1563413318.git.jpoimboe@redhat.com
parent 9fe7b764

tools/objtool/arch.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -15,6 +15,7 @@ enum insn_type { 
	INSN_JUMP_CONDITIONAL,

	INSN_JUMP_CONDITIONAL,

	INSN_JUMP_UNCONDITIONAL,

	INSN_JUMP_UNCONDITIONAL,

	INSN_JUMP_DYNAMIC,

	INSN_JUMP_DYNAMIC,

	INSN_JUMP_DYNAMIC_CONDITIONAL,

	INSN_CALL,

	INSN_CALL,

	INSN_CALL_DYNAMIC,

	INSN_CALL_DYNAMIC,

	INSN_RETURN,

	INSN_RETURN,

tools/objtool/check.c

+10 −2
Original line number Original line Diff line number Diff line
@@ -575,7 +575,11 @@ static int add_jump_destinations(struct objtool_file *file) 
			 * Retpoline jumps are really dynamic jumps in

			 * Retpoline jumps are really dynamic jumps in

			 * disguise, so convert them accordingly.

			 * disguise, so convert them accordingly.

			 */

			 */

			if (insn->type == INSN_JUMP_UNCONDITIONAL)

				insn->type = INSN_JUMP_DYNAMIC;

				insn->type = INSN_JUMP_DYNAMIC;

			else

				insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;



			insn->retpoline_safe = true;

			insn->retpoline_safe = true;

			continue;

			continue;

		} else {

		} else {
@@ -2114,14 +2118,18 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, 
			break;

			break;





		case INSN_JUMP_DYNAMIC:

		case INSN_JUMP_DYNAMIC:

		case INSN_JUMP_DYNAMIC_CONDITIONAL:

			if (func && is_sibling_call(insn)) {

			if (func && is_sibling_call(insn)) {

				ret = validate_sibling_call(insn, &state);

				ret = validate_sibling_call(insn, &state);

				if (ret)

				if (ret)

					return ret;

					return ret;

			}

			}





			if (insn->type == INSN_JUMP_DYNAMIC)

				return 0;

				return 0;





			break;



		case INSN_CONTEXT_SWITCH:

		case INSN_CONTEXT_SWITCH:

			if (func && (!next_insn || !next_insn->hint)) {

			if (func && (!next_insn || !next_insn->hint)) {

				WARN_FUNC("unsupported instruction in callable function",

				WARN_FUNC("unsupported instruction in callable function",