On Wed, Aug 2, 2023 at 3:56 PM Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > On Tue, 1 Aug 2023 20:40:54 -0400 > Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > On Wed, 2 Aug 2023 09:21:46 +0900 > > Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> wrote: > > > > > > Then use kprobes. When I asked Masami what the difference between fprobes > > > > and kprobes was, he told me that it would be that it would no longer rely > > > > on the slower FTRACE_WITH_REGS. But currently, it still does. > > > > > > kprobes needs to keep using pt_regs because software-breakpoint exception > > > handler gets that. And fprobe is used for bpf multi-kprobe interface, > > > but I think it can be optional. > > > > > > So until user-land tool supports the ftrace_regs, you can just disable > > > using fprobes if CONFIG_DYNAMIC_FTRACE_WITH_REGS=n > > > > I'm confused. I asked about the difference between kprobes on ftrace > > and fprobes, and you said it was to get rid of the requirement of > > FTRACE_WITH_REGS. > > > > https://lore.kernel.org/all/20230120205535.98998636329ca4d5f8325bc3@xxxxxxxxxx/ > > Yes, it is for enabling fprobe (and fprobe-event) on more architectures. > I don't think it's possible to change everything at once. So, it will be > changed step by step. At the first step, I will replace pt_regs with > ftrace_regs, and make bpf_trace.c and fprobe_event depends on > FTRACE_WITH_REGS. Just a small note that, strictly speaking, CONFIG_DYNAMIC_FTRACE_WITH_REGS=y is not enough. fprobe_init() would also need a way to set FTRACE_OPS_FL_SAVE_REGS conditionally. (you could be on an arch that supports saving either regs or args and if you don't set FTRACE_OPS_FL_SAVE_REGS you'd go through the args trampoline and get a ftrace_regs that doesn't hold a pt_regs)
