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From: Masami Hiramatsu <mhiramat@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	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,
	Jiri Olsa <jolsa@kernel.org>
Subject: Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines
Date: Tue, 10 May 2022 18:10:12 +0900	[thread overview]
Message-ID: <20220510181012.d5cba23a2547f14d14f016b9@kernel.org> (raw)
In-Reply-To: <20220509142203.6c4f2913@gandalf.local.home>

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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  reply	other threads:[~2022-05-10  9:11 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 [this message]
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
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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