On Wed, 2 Aug 2023 00:02:28 +0900 Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> wrote: > > If it diverges from that it's a big issue for bpf. > > We'd have to remove all of fprobe usage. > > I could be missing something, of course. > > Yes, so that's the discussion point. At first, I will disable fprobe on BPF > if ftrace_regs is not compatible with pt_regs, but eventually it should be > handled to support arm64. I believe BPF can do it since ftrace can do. Note, for FYI let me give you a little history of where ftrace_regs came from. When I realized that all function tracing had to save all the registers that represent the arguments of a function as well as the stack pointer, I wanted to change the non FTRACE_WITH_REGS to be able to have access to those registers. This is where FTRACE_WITH_ARGS came from. My first attempt was to pass a pt_regs that was partially filled, with only the registers required for the arguments. But the x86 maintainers NACK'd that. They refused to allow a partially filled pt_regs as that could cause bugs in the future when a user may assume that the pt_regs is filled but is not. The solution was to come up with ftrace_regs, which just means it has all the registers to extract the arguments of a function and nothing more. Most implementations just have a partially filled pt_regs within it, but an API needs to be used to get to the argument values. When you say BPF uses pt_regs, is the pt_regs full or does it get passed a partially filled structure? For fast function entry, ftrace_regs is what should be used if the pt_regs is not filled. As it is only for use for function entry. It supplies all regs and stack pointer to get to all the arguments. -- Steve