objtool: Support conditional retpolines (b68b9907) · Commits · 戴 / test

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:

Nick Desaulniers <ndesaulniers@google.com> Signed-off-by:

Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by:

Thomas Gleixner <tglx@linutronix.de> Tested-by:

Nick Desaulniers <ndesaulniers@google.com> Acked-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/30d4c758b267ef487fb97e6ecb2f148ad007b554.1563413318.git.jpoimboe@redhat.com

tools/objtool/arch.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -15,6 +15,7 @@ enum insn_type {
		INSN_JUMP_CONDITIONAL,
		INSN_JUMP_UNCONDITIONAL,
		INSN_JUMP_DYNAMIC,
		INSN_JUMP_DYNAMIC_CONDITIONAL,
		INSN_CALL,
		INSN_CALL_DYNAMIC,
		INSN_RETURN,

tools/objtool/check.c

+10 −2

Original line number	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
		* disguise, so convert them accordingly.
		*/
		if (insn->type == INSN_JUMP_UNCONDITIONAL)
		insn->type = INSN_JUMP_DYNAMIC;
		else
		insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;

		insn->retpoline_safe = true;
		continue;
		} else {
		@@ -2114,14 +2118,18 @@ static int validate_branch(struct objtool_file file, struct symbol func,
		break;

		case INSN_JUMP_DYNAMIC:
		case INSN_JUMP_DYNAMIC_CONDITIONAL:
		if (func && is_sibling_call(insn)) {
		ret = validate_sibling_call(insn, &state);
		if (ret)
		return ret;
		}

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

		break;

		case INSN_CONTEXT_SWITCH:
		if (func && (!next_insn \|\| !next_insn->hint)) {
		WARN_FUNC("unsupported instruction in callable function",

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