Re: [PATCH RFCv3 10/23] uprobes/x86: Add support to emulate nop5 instruction

[Jiri Olsa]

On Fri, Apr 04, 2025 at 01:33:11PM -0700, Andrii Nakryiko wrote:
> On Thu, Mar 20, 2025 at 4:43 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > Adding support to emulate nop5 as the original uprobe instruction.
> >
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> >  arch/x86/kernel/uprobes.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >
> 
> This optimization is independent from the sys_uprobe, right? Maybe
> send it as a stand-alone patch and let's land it sooner?

ok, will send it separately

> Also, how hard would it be to do the same for other nopX instructions?

will check, might be easy

thanks,
jirka

> 
> 
> > diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> > index 5ee2cce4c63e..1661e0ab2a3d 100644
> > --- a/arch/x86/kernel/uprobes.c
> > +++ b/arch/x86/kernel/uprobes.c
> > @@ -308,6 +308,11 @@ static int uprobe_init_insn(struct arch_uprobe *auprobe, struct insn *insn, bool
> >         return -ENOTSUPP;
> >  }
> >
> > +static int is_nop5_insn(uprobe_opcode_t *insn)
> > +{
> > +       return !memcmp(insn, x86_nops[5], 5);
> > +}
> > +
> >  #ifdef CONFIG_X86_64
> >
> >  asm (
> > @@ -865,6 +870,11 @@ void arch_uprobe_clear_state(struct mm_struct *mm)
> >         hlist_for_each_entry_safe(tramp, n, &state->head_tramps, node)
> >                 destroy_uprobe_trampoline(tramp);
> >  }
> > +
> > +static bool emulate_nop5_insn(struct arch_uprobe *auprobe)
> > +{
> > +       return is_nop5_insn((uprobe_opcode_t *) &auprobe->insn);
> > +}
> >  #else /* 32-bit: */
> >  /*
> >   * No RIP-relative addressing on 32-bit
> > @@ -878,6 +888,10 @@ static void riprel_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> >  static void riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> >  {
> >  }
> > +static bool emulate_nop5_insn(struct arch_uprobe *auprobe)
> > +{
> > +       return false;
> > +}
> >  #endif /* CONFIG_X86_64 */
> >
> >  struct uprobe_xol_ops {
> > @@ -1109,6 +1123,8 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
> >                 break;
> >
> >         case 0x0f:
> > +               if (emulate_nop5_insn(auprobe))
> > +                       goto setup;
> >                 if (insn->opcode.nbytes != 2)
> >                         return -ENOSYS;
> >                 /*
> > --
> > 2.49.0
> >