On Wed, 2 Aug 2023 17:47:03 +0200 Florent Revest <revest@xxxxxxxxxxxx> wrote: > 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") Thanks for the work! I also pushed my patches on https://kernel.googlesource.com/pub/scm/linux/kernel/git/mhiramat/linux/+/refs/heads/topic/fprobe-ftrace-regs 628e6c19d7dc ("tracing/fprobe: Enable fprobe events with CONFIG_DYNAMIC_FTRACE_WITH_ARGS") 311c98c29cfd ("fprobe: Use fprobe_regs in fprobe entry handler") This doesn't cover arm64 and rethook, but provides ftrace_regs optimized fprobe-event code, which uses a correct APIs for ftrace_regs. For the rethook we still need to provide 2 version for kretprobe(pt_regs) and fprobe(ftrace_regs). I think eventually we should replace the kretprobe with fprobe, but current rethook is tightly coupled with kretprobe and the kretprobe needs pt_regs. So, I would like to keep arm64 kretprobe impl, and add new rethook with ftrace_regs. Or, maybe we need these 2 configs intermediately. CONFIG_RETHOOK_WITH_REGS - in this case, kretprobe uses rethook CONFIG_RETHOOK_WITH_ARGS - in this case, kretprobe uses its own stack The problem is ftrace_regs only depends on CONFIG_DYNAMIC_FTRACE_WITH_*. Thank you, -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
