Re: [PATCH 2/2] ftrace/x86/extable: Add is_ftrace_trampoline() function

From: Thomas Gleixner
Date: Wed Nov 19 2014 - 13:29:33 EST

On Wed, 19 Nov 2014, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>
> Date: Tue, 18 Nov 2014 21:14:11 -0500
> Subject: [PATCH] ftrace/x86/extable: Add is_ftrace_trampoline() function
> 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.
> Link:
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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