On Tue, Oct 22, 2019 at 05:04:30PM -0400, Steven Rostedt wrote: > > I gave a solution for this. And that is to add another flag to allow > for just the minimum to change the ip. And we can even add another flag > to allow for changing the stack if needed (to emulate a call with the > same parameters).
your solution is to reduce the overhead. my solution is to remove it competely. See the difference? > By doing this work, live kernel patching will also benefit. Because it > is also dealing with the unnecessary overhead of saving regs. > > And we could possibly even have kprobes benefit from this if a kprobe > doesn't need full regs. Neither of two statements are true. The per-function generated trampoline I'm talking about is bpf specific. For a function with two arguments it's just: push rbp mov rbp, rsp push rdi push rsi lea rdi,[rbp-0x10] call jited_bpf_prog pop rsi pop rdi leave ret fentry's nop is replaced with call to the above. That's it. kprobe and live patching has no use out of it. > But you said that you can't have this and trace the functions at the > same time. Which also means you can't do live kernel patching on these > functions either. I don't think it's a real use case, but to avoid further arguing I'll add one nop to the front of generated bpf trampoline so that ftrace and livepatch can use it.
