Re: [PATCH v16 0/4] perf: Support the deferred unwinding infrastructure

Peter Zijlstra
2025-11-05T13:08:48Z

On Tue, Nov 04, 2025 at 12:22:01PM +0100, Florian Weimer wrote:
> * Peter Zijlstra:
>
> > +/*
> > + * Heuristic-based check if uprobe is installed at the function entry.
> > + *
> > + * Under assumption of user code being compiled with frame pointers,
> > + * `push %rbp/%ebp` is a good indicator that we indeed are.
> > + *
> > + * Similarly, `endbr64` (assuming 64-bit mode) is also a common pattern.
> > + * If we get this wrong, captured stack trace might have one extra bogus
> > + * entry, but the rest of stack trace will still be meaningful.
> > + */
> > +bool is_uprobe_at_func_entry(struct pt_regs *regs)
>
> Is this specifically for uprobes? Wouldn't it make sense to tell the
> kernel when the uprobe is installed whether the frame pointer has been
> set up at this point? Userspace can typically figure this out easily
> enough (it's not much more difficult to find the address of the
> function).

Yeah, I suppose so. Not sure the actual user interface for this allows
for that. Someone would have to dig into that a bit.