Messages in this thread | | | Date | Tue, 10 May 2022 18:10:12 +0900 | From | Masami Hiramatsu <> | Subject | Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines |
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Hi Steve,
On Mon, 9 May 2022 14:22:03 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> On Thu, 5 May 2022 12:15:38 +0900 > Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > OK. But my interest is that the ftrace on arm64 can provide a limited > > access to registers via pt_regs or not. I don't mind the contained values > > so much because in the most case, 'users' will (most likely) access to the > > ARGs via BPF or tracefs (and we can just warn users if they try to access > > the registers which is not saved.) But if the arm64 ftrace only provides > > a special data structure, arch-independent code must have 2 different access > > code. That is inefficient. That is my concern. > > IOW, I'm interested in interface abstraction. > > Note, ftrace now has a ftrace_regs structure that is passed to the > callbacks for the function tracer. > > It then has an arch dependent helper function ftrace_get_regs(fregs), that > returns a pt_regs from the fregs only if the fregs has a full pt_regs to > return. If not, it returns NULL. > > This was suggested by both Peter Zijlstra and Thomas Gleixner when I > introduced FTRACE_WITH_ARGS, where all functions can now get the arguments > from fregs, but not the full pt_regs.
Hmm, I thought the ftrace_get_regs() is the all-or-nothing interface, or is there any way to get the arguments from fregs?
> If a ftrace_ops has the REGS flag set > (using ftrace_regs_caller), the ftrace_get_regs(fregs) will return the > pt_regs, or it will return NULL if ftrace_regs_caller was not used. > > This way the same parameter can provide full pt_regs or a subset, and have > an generic interface to tell the difference.
If it can provide a partial (subset of) pt_regs, that could be good for me too, since at least kprobe-events on ftrace can check the traced register is in the subset or not and reject it if it doesn't saved.
Thank you,
-- Masami Hiramatsu <mhiramat@kernel.org>
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