linux-kernel - Re: [PATCH] ftrace/x86: Fix function graph tracer reset path

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Message-ID: <20160515214101.GA6574@codeblueprint.co.uk>
Date:	Sun, 15 May 2016 22:41:01 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Namhyung Kim <namhyung@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
	Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH] ftrace/x86: Fix function graph tracer reset path

On Fri, 13 May, at 10:06:10AM, Steven Rostedt wrote:
> Matt,
> 
> This bug looks very similar to what you were hitting with the function
> profiler. Can you apply this patch and see if it fixes the issue for
> you.

Yep, this patch fixes it for me.

For the record, this is what objdump tells me (with patch applied),

00000000000000b6 <ftrace_epilogue>:
  b6:   eb 03                   jmp    bb <ftrace_stub>
  b8:   90                      nop
  b9:   90                      nop
  ba:   90                      nop

So my toolchain is definitely generating a short jump. This is
binutils 2.26.

But on one of my other test machines with binutils 2.24 I see this,

00000000000000aa <ftrace_epilogue>:
  aa:   e9 00 00 00 00          jmpq   af <ftrace_stub>
                        ab: R_X86_64_PC32       ftrace_stub-0x4

i.e. a near jump.