Re: [PATCH RFCv2 08/18] uprobes/x86: Add uprobe syscall to speed up uprobe

Alexei Starovoitov
2025-02-26T02:37:08Z

On Tue, Feb 25, 2025 at 10:06 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Tue, Feb 25, 2025 at 5:35 AM Jiri Olsa <olsajiri@gmail.com> wrote:
> >
> > > In later patches I see nop5 is replaced with a call to
> > > uprobe_trampoline_entry, but which part saves
> > > rdi and other regs?
> > > Compiler doesn't automatically spill/fill around USDT's nop/nop5.
> > > Selftest is doing:
> > > +__naked noinline void uprobe_test(void)
> > > so just lucky ?
> >
> > if you mean registers that would carry usdt arguments, ebpf programs
> > access those based on assembler operand string stored in usdt record:
>
> No. I'm talking about all normal registers that trap-style uprobe
> preserves, but this nop5->call will scratch.
> Instead of void uprobe_test(void)
> add some arguments to it, and read them before and after nop5 uprobe.
> They must remain the same.

Ignore me. It's a syscall insn. All fine.