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. > > At this point, we can split the problem into two, how to move bpf on > ftrace_regs and how to move fprobe-event on ftrace_regs. fprobe-event > change is not hard because it is closing in the kernel and I can do it. > But for BPF, I need to ask BPF user-land tools to support ftrace_regs. Ah! I finally found the branch where I had pushed my proof of concept of fprobe with ftrace_regs... it's a few months old and I didn't get it in a state such that it could be sent to the list but maybe this can save you a little bit of lead time Masami :) (especially the bpf and arm64 specific bits) https://github.com/FlorentRevest/linux/commits/bpf-arm-complete 08afb628c6e1 ("ftrace: Add a macro to forge an incomplete pt_regs from a ftrace_regs") 203e96fe1790 ("fprobe, rethook: Use struct ftrace_regs instead of struct pt_regs") 1a9e280b9b16 ("arm64,rethook,kprobes: Replace kretprobe with rethook on arm64") 7751c6db9f9d ("bpf: Fix bpf get_func_ip() on arm64 multi-kprobe programs") a10c49c0d717 ("selftests/bpf: Update the tests deny list on aarch64")
