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

Peter Zijlstra
2022-09-07T09:40:21Z

On Wed, Sep 07, 2022 at 09:06:12AM +0000, David Laight wrote:
> From: Peter Zijlstra
> > Sent: 07 September 2022 10:01
> >
> > 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.
>
> Do they ever appear in the kernel?

No; that is, not on any of the random vmlinux.o images I checked this
morning.

Still, best to properly decode them anyway.