linux-kernel - Re: [RFC][PATCH 3/5] ftrace/x86_32: Add stack frame pointer to ftrace

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Message-ID: <20170315211308.nprwbpmrzuwpvire@treble>
Date:   Wed, 15 Mar 2017 16:13:08 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...capital.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC][PATCH 3/5] ftrace/x86_32: Add stack frame pointer to
 ftrace_caller

On Wed, Mar 15, 2017 at 03:55:30PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> The function hook ftrace_caller does not create its own stack frame, and
> this causes the ftrace stack trace to miss the first function when doing
> stack traces.
> 
>  # echo schedule:stacktrace > /sys/kernel/tracing/set_ftrace_filter
> 
> Before:
>          <idle>-0     [002] .N..    29.865807: <stack trace>
>  => cpu_startup_entry
>  => start_secondary
>  => startup_32_smp
>            <...>-7     [001] ....    29.866509: <stack trace>
>  => kthread
>  => ret_from_fork
>            <...>-1     [000] ....    29.865377: <stack trace>
>  => poll_schedule_timeout
>  => do_select
>  => core_sys_select
>  => SyS_select
>  => do_fast_syscall_32
>  => entry_SYSENTER_32
> 
> After:
>           <idle>-0     [002] .N..    31.234853: <stack trace>
>  => do_idle
>  => cpu_startup_entry
>  => start_secondary
>  => startup_32_smp
>            <...>-7     [003] ....    31.235140: <stack trace>
>  => rcu_gp_kthread
>  => kthread
>  => ret_from_fork
>            <...>-1819  [000] ....    31.264172: <stack trace>
>  => schedule_hrtimeout_range
>  => poll_schedule_timeout
>  => do_sys_poll
>  => SyS_ppoll
>  => do_fast_syscall_32
>  => entry_SYSENTER_32
> 
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
>  arch/x86/kernel/ftrace_32.S | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S
> index 4ff30f31f0a5..73d61a62649d 100644
> --- a/arch/x86/kernel/ftrace_32.S
> +++ b/arch/x86/kernel/ftrace_32.S
> @@ -17,12 +17,19 @@ ENTRY(mcount)
>  END(mcount)
>  
>  ENTRY(ftrace_caller)
> +
> +	pushl %ebp
> +	movl %esp, %ebp
> +

The operands for the above two instructions should be vertically aligned
like the rest of the code.  Otherwise:

Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh