linux-kernel - Re: [PATCH v7 2/3] ftrace: introduce FTRACE_IP

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Date:   Tue, 7 Jan 2020 19:05:47 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Corbet <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v7 2/3] ftrace: introduce FTRACE_IP_EXTENSION

On Wed, 25 Dec 2019 09:42:52 +0000
Jisheng Zhang <Jisheng.Zhang@...aptics.com> wrote:

> On some architectures, the DYNAMIC_FTRACE_WITH_REGS is implemented by
> gcc's -fpatchable-function-entry option. Take arm64 for example, arm64
> makes use of GCC -fpatchable-function-entry=2 option to insert two
> nops. When the function is traced, the first nop will be modified to
> the LR saver, then the second nop to "bl <ftrace-entry>". we need to
> update ftrace_location() to recognise these two instructions  as being
> part of ftrace. To do this, we introduce FTRACE_IP_EXTENSION to let
> ftrace_location search IP, IP + FTRACE_IP_EXTENSION range.
> 
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
> Suggested-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

You can also add:

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

and when Masami is happy with your patches, it should go through the
tip tree.

Thanks!

-- Steve

> ---
>  include/linux/ftrace.h | 4 ++++
>  kernel/trace/ftrace.c  | 2 +-
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 7247d35c3d16..05a03b2a2f39 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -20,6 +20,10 @@
>  
>  #include <asm/ftrace.h>
>  
> +#ifndef FTRACE_IP_EXTENSION
> +#define  FTRACE_IP_EXTENSION 0
> +#endif
> +
>  /*
>   * If the arch supports passing the variable contents of
>   * function_trace_op as the third parameter back from the
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 74439ab5c2b6..a8cfea502369 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1590,7 +1590,7 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
>   */
>  unsigned long ftrace_location(unsigned long ip)
>  {
> -	return ftrace_location_range(ip, ip);
> +	return ftrace_location_range(ip, ip + FTRACE_IP_EXTENSION);
>  }
>  
>  /**