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Date:   Mon, 4 Jun 2018 16:16:12 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Thomas Garnier <thgarnie@google.com>
Cc:     kernel-hardening@lists.openwall.com,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Francis Deslauriers <francis.deslauriers@efficios.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Guenter Roeck <linux@roeck-us.net>,
        nixiaoming <nixiaoming@huawei.com>,
        James Hogan <jhogan@kernel.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 21/27] x86/ftrace: Adapt function tracing for PIE
 support
Message-ID: <20180604161612.6d48d8d2@gandalf.local.home>
In-Reply-To: <20180529221625.33541-22-thgarnie@google.com>
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        <20180529221625.33541-22-thgarnie@google.com>
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On Tue, 29 May 2018 15:15:22 -0700
Thomas Garnier <thgarnie@google.com> wrote:

> When using -fPIE/PIC with function tracing, the compiler generates a
> call through the GOT (call *__fentry__@GOTPCREL). 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 <thgarnie@google.com>
> ---
>