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From: Steven Rostedt <rostedt@goodmis.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: "Wangshaobo (bobo)" <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 0/4] arm64/ftrace: support dynamic trampoline
Date: Wed, 25 May 2022 09:58:45 -0400	[thread overview]
Message-ID: <20220525095845.53ec8fe0@gandalf.local.home> (raw)
In-Reply-To: <Yo4k2Y8oNcKG5ca0@FVFF77S0Q05N>

On Wed, 25 May 2022 13:45:13 +0100
Mark Rutland <mark.rutland@arm.com> wrote:

> ... the compiler places 3 NOPs *before* any BTI, and 2 NOPs *after* any BTI,
> still recording the location of the first NOP. So in the two cases we get:
> 
> 		NOP		<--- recorded location
> 		NOP
> 		NOP
> 	__func_without_bti:
> 		NOP
> 		NOP
> 
> 		NOP		<--- recorded location
> 		NOP
> 		NOP
> 	__func_with_bti:
> 		BTI
> 		NOP
> 		NOP

Are you saying that the above "recorded location" is what we have in
mcount_loc section? If that's the case, we will need to modify it to point
to something that kallsyms will recognize (ie. sym+0 or greater). Because
that will cause set_ftrace_filter to fail as well.

-- Steve


> 
> ... so where we want to patch one of the later nops to banch to a pre-function
> NOP, we need to know whether or not the compiler generated a BTI. We can
> discover discover that either by:
> 
> * Checking whether the recorded location is at sym+0 (no BTI) or sym+4 (BTI).
> 
> * Reading the instruction before the recorded location, and seeing if this is a
>   BTI.
> 
> ... and depending on how we handle thigns the two cases *might* need different
> trampolines.


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  reply	other threads:[~2022-05-25 14:00 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
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 [this message]
2022-05-25 17:26           ` Mark Rutland
2022-04-21 12:53 ` Mark Rutland

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