Re: Patch "ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it" has been added to the 4.4-stable tree

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Jan 20, 2017 at 10:17:57AM +0100, Jiri Slaby wrote:
> On 01/06/2017, 03:55 PM, gregkh@linuxfoundation.org wrote:
> > From 847fa1a6d3d00f3bdf68ef5fa4a786f644a0dd67 Mon Sep 17 00:00:00 2001
> > From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
> > Date: Thu, 8 Dec 2016 12:48:26 -0500
> > Subject: ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it
> > 
> > From: Steven Rostedt (Red Hat) <rostedt@goodmis.org>
> > 
> > commit 847fa1a6d3d00f3bdf68ef5fa4a786f644a0dd67 upstream.
> > 
> > With new binutils, gcc may get smart with its optimization and change a jmp
> > from a 5 byte jump to a 2 byte one even though it was jumping to a global
> > function. But that global function existed within a 2 byte radius, and gcc
> > was able to optimize it. Unfortunately, that jump was also being modified
> > when function graph tracing begins. Since ftrace expected that jump to be 5
> > bytes, but it was only two, it overwrote code after the jump, causing a
> > crash.
> > 
> > This was fixed for x86_64 with commit 8329e818f149, with the same subject as
> > this commit, but nothing was done for x86_32.
> 
> Greg,
> 
> can we have the x86_64 fix (8329e818f149) in 4.4 too?

Ah, yes, I totally missed that.  I'll queue it up after this next round
of kernels goes out in a few hours.

thanks,

greg k-h