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

Jiri Olsa
2025-04-07T11:07:30Z

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@kernel.org> wrote:
> >
> > Adding support to emulate nop5 as the original uprobe instruction.
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> > 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
> >