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Message-ID: <20220421083758.37b239a4@gandalf.local.home>
Date: Thu, 21 Apr 2022 08:37:58 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Wangshaobo (bobo)" <bobo.shaobowang@...wei.com>
Cc: <cj.chengjian@...wei.com>, <huawei.libin@...wei.com>,
<xiexiuqi@...wei.com>, <liwei391@...wei.com>,
<linux-kernel@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>, <catalin.marinas@....com>,
<will@...nel.org>, <mark.rutland@....com>,
<zengshun.wu@...look.com>
Subject: Re: [RFC PATCH -next v2 0/4] arm64/ftrace: support dynamic
trampoline
On Thu, 21 Apr 2022 09:13:01 +0800
"Wangshaobo (bobo)" <bobo.shaobowang@...wei.com> wrote:
> Not yet, Steve, ftrace_location() looks has no help to find a right
> rec->ip in our case,
>
> ftrace_location() can find a right rec->ip when input ip is in the range
> between
>
> sym+0 and sym+$end, but our question is how to identify rec->ip from
> __mcount_loc,
Are you saying that the "ftrace location" is not between sym+0 and sym+$end?
>
> this changed the patchable entry before bti to after in gcc:
>
> [1] https://reviews.llvm.org/D73680
>
> gcc tells the place of first nop of the 5 NOPs when using
> -fpatchable-function-entry=5,3,
>
> but not tells the first nop after bti, so we don't know how to adjust
> our rec->ip for ftrace.
OK, so I do not understand how the compiler is injecting bti with mcount
calls, so I'll just walk away for now ;-)
-- Steve
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