[PATCH] objtool,x86: Teach decode about LOOP* instructions

Peter Zijlstra
2022-09-07T09:01:36Z

On Wed, Sep 07, 2022 at 09:06:45AM +0200, Peter Zijlstra wrote:
> On Wed, Sep 07, 2022 at 09:55:21AM +0900, Masami Hiramatsu (Google) wrote:
>
> > +/* Return the jump target address or 0 */
> > +static inline unsigned long insn_get_branch_addr(struct insn *insn)
> > +{
> > + switch (insn->opcode.bytes[0]) {
> > + case 0xe0: /* loopne */
> > + case 0xe1: /* loope */
> > + case 0xe2: /* loop */
>
> Oh cute, objtool doesn't know about those, let me go add them.

---
Subject: objtool,x86: Teach decode about LOOP* instructions

With kprobes also needing to follow control flow; it was found that
objtool is missing the branches from the LOOP* instructions.

Reported-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.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;
/*