On Tue, 17 Sep 2024 11:08:48 +0100 Will Deacon <w...@kernel.org> wrote:
> > > @@ -787,6 +789,9 @@ __ftrace_return_to_handler(struct ftrace_regs *fregs, > > > unsigned long frame_pointe > > > } > > > > > > trace.rettime = trace_clock_local(); > > > + if (fregs) > > > + ftrace_regs_set_instruction_pointer(fregs, ret); > > Where does the instruction pointer get used after this? The arm64 > 'return_to_handler' function doesn't look at it when we return. It's for the hooks to the return instruction. kretprobes will start using function graph tracer to hook to a return of a function (via fprobes), and the callbacks will need access to the return pointer. The callbacks get passed the ftrace_regs, and this is how they can see what the function is returning to. For example, BPF programs will need this. So it's not needed for the infrastructure, only the callbacks that hook to it. -- Steve
