[tip: objtool/core] objtool,x86: Teach decode about LOOP* instructions

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     7a7621dfa417aa3715d2a3bd1bdd6cf5018274d0
Gitweb:        https://git.kernel.org/tip/7a7621dfa417aa3715d2a3bd1bdd6cf5018274d0
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Wed, 07 Sep 2022 11:01:20 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 15 Sep 2022 16:13:55 +02:00

objtool,x86: Teach decode about LOOP* instructions

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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/Yxhd4EMKyoFoH9y4@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
 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 c260006..1c253b4 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;
 		/*