linux-kernel - Re: [PATCH] stop_machine: Mark functions as notrace

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Date:   Fri, 30 Oct 2020 20:28:18 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Atish Patra <atishp@...shpatra.org>
Cc:     Guo Ren <guoren@...nel.org>, Zong Li <zong.li@...ive.com>,
        Paul McKenney <paulmck@...nel.org>, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        joel@...lfernandes.org, vincent.whitchurch@...s.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Greentime Hu <greentime.hu@...ive.com>,
        Colin Ian King <colin.king@...onical.com>,
        rcu@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH] stop_machine: Mark functions as notrace

On Fri, 30 Oct 2020 14:47:56 -0700
Atish Patra <atishp@...shpatra.org> wrote:

> > Look at arm64, they __kprobes flag and I guess it would also prevent
> > ftrace call site.
> >  
> 
> Are you sure about that ? __kprobes puts the code in .kprobes.text section
> which is under whitelist sections in recordmcount.pl & recordmcount.c.

Correct, ftrace can trace functions marked with __kprobes. That said,
the instruction you are looking at here, is in a file that is
blacklisted from recordmcount.

  CFLAGS_REMOVE_insn.o = $(CC_FLAGS_FTRACE)

All ftrace flags are removed from the compiling of insn.c, and every
function in that file will not be traced.

-- Steve