linux-kernel - Re: [linux-stable-rc:linux-5.10.y 6996/7120] arch/x86/kernel/ftrace_64.o: warning: objtool: ftrace

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Message-ID: <20220714001842.drzq7oeyk4akk2xo@treble>
Date:   Wed, 13 Jul 2022 17:18:42 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Ben Hutchings <bwh@...nel.org>
Cc:     kernel test robot <lkp@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [linux-stable-rc:linux-5.10.y 6996/7120]
 arch/x86/kernel/ftrace_64.o: warning: objtool: ftrace_epilogue()+0x10:
 unreachable instruction

On Thu, Jul 14, 2022 at 01:41:58AM +0200, Ben Hutchings wrote:
> On Wed, 2022-07-13 at 03:57 +0800, kernel test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-5.10.y
> > head:   ba398a0e54049bb6a1c102245ae84103f103ff2c
> > commit: 8ca9dceaa17983afec1cc8e1a6e76d6bd142447a [6996/7120] objtool: Assume only ELF functions do sibling calls
> > config: x86_64-rhel-8.3-syz (https://download.01.org/0day-ci/archive/20220713/202207130344.dwXyDmTk-lkp@intel.com/config)
> > compiler: gcc-11 (Debian 11.3.0-3) 11.3.0
> > reproduce (this is a W=1 build):
> >         # https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/commit/?id=8ca9dceaa17983afec1cc8e1a6e76d6bd142447a
> >         git remote add linux-stable-rc https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
> >         git fetch --no-tags linux-stable-rc linux-5.10.y
> >         git checkout 8ca9dceaa17983afec1cc8e1a6e76d6bd142447a
> >         # save the config file
> >         mkdir build_dir && cp config build_dir/.config
> >         make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash arch/x86/
> > 
> > If you fix the issue, kindly add following tag where applicable
> > Reported-by: kernel test robot <lkp@...el.com>
> > 
> > All warnings (new ones prefixed by >>):
> > 
> > > > arch/x86/kernel/ftrace_64.o: warning: objtool: ftrace_epilogue()+0x10: unreachable instruction
> > 
> > 
> > objdump-func vmlinux.o ftrace_epilogue:
> > 0000 000000000008ca70 <ftrace_epilogue>:
> > 0000    8ca70:	e9 00 00 00 00       	jmp    8ca75 <ftrace_epilogue+0x5>	8ca71: R_X86_64_PLT32	ftrace_stub-0x4
> > 0005    8ca75:	66 66 2e 0f 1f 84 00 00 00 00 00 	data16 cs nopw 0x0(%rax,%rax,1)
> > 
> 
> I don't know what's going on here.  There's a jump to a ret (now
> potentialy a rethunk), and nothing obviously unreachable. 
> ftrace_epilogue got simplified by commit 0c0593b45c9b "x86/ftrace: Make
> function graph use ftrace directly" which maybe avoids the warning in
> the mainline.

The unreachable warning is actually pointing to ftrace_stub().  I think
you need

  18660698a3d3 ("x86/ftrace: Add UNWIND_HINT_FUNC annotation for ftrace_stub")

-- 
Josh