[PATCH AUTOSEL 6.0 10/32] objtool,x86: Teach decode about LOOP* instructions

Sasha Levin
2022-10-18T00:08:54Z

From: Peter Zijlstra <peterz@infradead.org>

[ Upstream commit 7a7621dfa417aa3715d2a3bd1bdd6cf5018274d0 ]

When 'discussing' control flow Masami mentioned the LOOP* instructions
and I realized objtool doesn't decode them properly.

As it turns out, these instructions are somewhat inefficient and as
such unlikely to be emitted by the compiler (a few vmlinux.o checks
can't find a single one) so this isn't critical, but still, best to
decode them properly.

Reported-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/Yxhd4EMKyoFoH9y4@hirez.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/objtool/arch/x86/decode.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index c260006106be..1c253b4b7ce0 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -635,6 +635,12 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
*type = INSN_CONTEXT_SWITCH;
break;

+ case 0xe0: /* loopne */
+ case 0xe1: /* loope */
+ case 0xe2: /* loop */
+ *type = INSN_JUMP_CONDITIONAL;
+ break;
+
case 0xe8:
*type = INSN_CALL;
/*
--
2.35.1