Re: [RFC PATCH] riscv: Implement HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS

[Robbin Ehn]

Hey,

> <index-in-dispatch-list>
> func_symbol:
> auipc t0, common_dispatch:high <=> j actual_func:
> jalr t0, common_dispatch:low(t0)
>

If you are patching in a jump, I don't see why you wouldn't jump over
ld+jalr? (no need for common dispatch)
Patching jalr with nop, and keeping auipc, addresses the issue with
having to jump in the disabled case.
But needs either common dispatch or per func dispatch.

Thanks, Robbin

> common_dispatch:
> load t1, index + dispatch-list
> ld t1, 0(t1)
> jr t1
>
>
> >
> > > However, one thing I am not very sure is: do we need a destination
> > > address in a "per-function" manner? It seems like most of the time the
> > > destination address can only be ftrace_call, or ftrace_regs_call. If
> > > the number of destination addresses is very few, then we could
> > > potentially reduce the size of
> > > <func_trace_target_data_8B_per_function>.
> >
> > Yes, we do need a per-function manner. BPF, e.g., uses
> > dynamically/JIT:ed trampolines/targets.
> >
> >
> >
> > Björn
>
> Cheers,
> Andy