linux-kernel - Re: [PATCH 2/2] ftrace/x86/extable: Add is_ftrace

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Date:	Wed, 19 Nov 2014 17:16:55 +0900
From:	Namhyung Kim <namhyung@...nel.org>
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>,
	"H. Peter Anvin" <hpa@...or.com>, williams@...hat.com,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 2/2] ftrace/x86/extable: Add is_ftrace_trampoline() function

Hi Steve,

On Tue, 18 Nov 2014 22:33:33 -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
>
> Stack traces that happen from function tracing check if the address
> on the stack is a __kernel_text_address(). That is, is the address
> kernel code. This calls core_kernel_text() which returns true
> if the address is part of the builtin kernel code. It also calls
> is_module_text_address() which returns true if the address belongs
> to module code.
>
> But what is missing is ftrace dynamically allocated trampolines.
> These trampolines are allocated for individual ftrace_ops that
> call the ftrace_ops callback functions directly. But if they do a
> stack trace, the code checking the stack wont detect them as they
> are neither core kernel code nor module address space.
>
> Adding another field to ftrace_ops that also stores the size of
> the trampoline assigned to it we can create a new function called
> is_ftrace_trampoline() that returns true if the address is a
> dynamically allocate ftrace trampoline. Note, it ignores trampolines
> that are not dynamically allocated as they will return true with
> the core_kernel_text() function.
>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>


[SNIP]
> @@ -102,6 +103,8 @@ int __kernel_text_address(unsigned long addr)
>  		return 1;
>  	if (is_module_text_address(addr))
>  		return 1;
> +	if (is_ftrace_trampoline(addr))
> +		return 1;

What about kernel_text_address()?  It seems some archs like ARM use it
instead of __kernel_text_address() although trampoline is only enabled
on x86 for now.

Thanks,
Namhyung

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