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Date: Mon, 4 Jun 2018 16:16:12 -0400
From: Steven Rostedt <>
To: Thomas Garnier <>
Cc:, Ingo Molnar <>,
 Thomas Gleixner <>, "H. Peter Anvin" <>,, Francis Deslauriers <>,
 Greg Kroah-Hartman <>, Andrew Morton
 <>, "Peter Zijlstra (Intel)"
 <>, Guenter Roeck <>, nixiaoming
 <>, James Hogan <>,
Subject: Re: [PATCH v4 21/27] x86/ftrace: Adapt function tracing for PIE

On Tue, 29 May 2018 15:15:22 -0700
Thomas Garnier <> wrote:

> When using -fPIE/PIC with function tracing, the compiler generates a
> call through the GOT (call *__fentry__@...PCREL). This instruction
> takes 6 bytes instead of 5 on the usual relative call.
> If PIE is enabled, replace the 6th byte of the GOT call by a 1-byte nop
> so ftrace can handle the previous 5-bytes as before.
> Position Independent Executable (PIE) support will allow to extend the
> KASLR randomization range 0xffffffff80000000.

I thought you were going to write a update to recordmcount.c to handle
this at compile time?

-- Steve

> Signed-off-by: Thomas Garnier <>
> ---

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