From: Mark Rutland <mark.rutland@arm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Wang ShaoBo <bobo.shaobowang@huawei.com>,
cj.chengjian@huawei.com, huawei.libin@huawei.com,
xiexiuqi@huawei.com, liwei391@huawei.com,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
will@kernel.org, zengshun.wu@outlook.com
Subject: Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines
Date: Wed, 4 May 2022 13:43:26 +0100 [thread overview]
Message-ID: <YnJ07mRU3wCd9G/G@lakrids> (raw)
In-Reply-To: <20220421130648.56b21951@gandalf.local.home>
On Thu, Apr 21, 2022 at 01:06:48PM -0400, Steven Rostedt wrote:
> On Thu, 21 Apr 2022 17:27:40 +0100
> Mark Rutland <mark.rutland@arm.com> wrote:
>
> > We can initialize the ops pointer to a default ops that does the whole
> > __do_for_each_ftrace_ops() dance.
>
> OK, I think I understand now. What you are doing is instead of creating a
> trampoline that has all the information in the trampoline, you add nops to
> all the functions where you can place the information in the nops (before
> the function), and then have the trampoline just read that information to
> find the ops pointer as well as the function to call.
FWIW, I had a go at mocking that up:
https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/ftrace/per-callsite-ops
Aside from some bodges required to ensure the patch site is suitably aligned
(which I think can be cleaned up somewhat), I don't think it looks that bad.
I wasn't sure how exactly to wire that up in the core code, so all the patch
sites are initialized with a default ops that calls
arch_ftrace_ops_list_func(), but it looks like it should be possible to wire
that up in the core with some refactoring.
> I guess you could have two trampolines as well. One that always calls the
> list loop, and one that calls the data stored in front of the function that
> was just called the trampoline. As it is always safe to call the loop
> function, you could have the call call that trampoline first, set up the
> specific data before the function, then call the trampoline that will read
> it.
I was thinking we could just patch the ops with a default ops that called the
list loop, as my patches default them to.
> And same thing for tear down.
I wasn't sure how teardown was meant to work in general. When we want to
remove an ops structure, or a trampoline, how do we ensure those are no
longer in use before we remove them? I can see how we can synchronize
the updates to the kernel text, but I couldn't spot how we handle a
thread being in the middle of a trampoline.
Thanks,
Mark.
next prev parent reply other threads:[~2022-05-04 12:43 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-16 10:01 [RFC PATCH -next v2 0/4] arm64/ftrace: support dynamic trampoline Wang ShaoBo
2022-03-16 10:01 ` [RFC PATCH -next v2 1/4] arm64: introduce aarch64_insn_gen_load_literal Wang ShaoBo
2022-03-16 10:01 ` [RFC PATCH -next v2 2/4] arm64/ftrace: introduce ftrace dynamic trampoline entrances Wang ShaoBo
2022-03-16 10:01 ` [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines Wang ShaoBo
2022-04-21 13:10 ` Mark Rutland
2022-04-21 14:06 ` Steven Rostedt
2022-04-21 14:08 ` Steven Rostedt
2022-04-21 15:14 ` Mark Rutland
2022-04-21 15:42 ` Steven Rostedt
2022-04-21 16:27 ` Mark Rutland
2022-04-21 17:06 ` Steven Rostedt
2022-04-22 10:12 ` Mark Rutland
2022-04-22 15:45 ` Steven Rostedt
2022-04-22 17:27 ` Mark Rutland
2022-04-26 8:47 ` Masami Hiramatsu
2022-05-04 10:24 ` Mark Rutland
2022-05-05 3:15 ` Masami Hiramatsu
2022-05-09 18:22 ` Steven Rostedt
2022-05-10 9:10 ` Masami Hiramatsu
2022-05-10 14:44 ` Steven Rostedt
2022-05-11 14:34 ` Masami Hiramatsu
2022-05-11 15:12 ` Steven Rostedt
2022-05-12 12:02 ` Masami Hiramatsu
2022-05-12 13:50 ` Steven Rostedt
2022-05-25 12:17 ` Mark Rutland
2022-05-25 13:43 ` Steven Rostedt
2022-05-25 17:12 ` Mark Rutland
2022-05-30 1:03 ` Masami Hiramatsu
2022-05-30 12:38 ` Jiri Olsa
2022-05-31 1:00 ` Masami Hiramatsu
2022-05-04 12:43 ` Mark Rutland [this message]
2022-05-05 2:57 ` Wangshaobo (bobo)
2022-05-25 12:27 ` Mark Rutland
2022-04-27 8:54 ` Wangshaobo (bobo)
2022-03-16 10:01 ` [RFC PATCH -next v2 4/4] arm64/ftrace: implement long jump for dynamic trampolines Wang ShaoBo
2022-04-21 13:47 ` Mark Rutland
2022-03-16 14:29 ` [RFC PATCH -next v2 0/4] arm64/ftrace: support dynamic trampoline Steven Rostedt
2022-04-20 18:11 ` Steven Rostedt
2022-04-21 1:13 ` Wangshaobo (bobo)
2022-04-21 12:37 ` Steven Rostedt
2022-05-25 12:45 ` Mark Rutland
2022-05-25 13:58 ` Steven Rostedt
2022-05-25 17:26 ` Mark Rutland
2022-04-21 12:53 ` Mark Rutland
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