linux-kernel - Re: [RFC][PATCH 5/5] ftrace/x86-32: Add -mfentry support to x86_32 with DYNAMIC

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Date:   Wed, 15 Mar 2017 16:55:45 -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 5/5] ftrace/x86-32: Add -mfentry support to x86_32
 with DYNAMIC_FTRACE set

On Wed, Mar 15, 2017 at 03:55:32PM -0400, Steven Rostedt wrote:
> +#ifdef USING_FRAME_POINTER
> +# ifdef CC_USING_FENTRY
> +	/*
> +	 * Frame pointers are of ip followed by bp.
> +	 * Since fentry is an immediate jump, we are left with
> +	 * parent-ip, function-ip. We need to add a frame with
> +	 * parent-ip followed by ebp.
> +	 */
> +	pushl 4(%esp)				/* parent ip */
>  	pushl %ebp
>  	movl %esp, %ebp
> -
> +	pushl 2*4(%esp)				/* function ip */
> +# endif
> +	/* For mcount, the function ip is directly above */
> +	pushl %ebp
> +	movl %esp, %ebp
> +#endif

More vertical operand alignment issues.

> @@ -85,6 +140,10 @@ ENTRY(ftrace_regs_caller)
>  	pushl	%edx
>  	pushl	%ecx
>  	pushl	%ebx
> +#ifndef USING_FRAME_POINTER
> +	/* Load 4 off of the parent ip addr into ebp */
> +	lea	14*4(%esp), %ebp
> +#endif

Instead of:

	#ifndef USING_FRAME_POINTER
	
Shouldn't it be:

	#ifdef CC_USING_FENTRY

?

Otherwise, if I'm reading it right, with fentry and
CONFIG_FRAME_POINTER=y, ebp will lead to the grandparent's ip instead of
the parent's ip.

-- 
Josh