linux-kernel - Re: Kernel build with gcc 8 a lot of warnings

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Message-ID: <20180508055126.GA18724@kroah.com>
Date:   Tue, 8 May 2018 07:51:26 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     damian <damian.tometzki@...oud.com>, peterz@...radead.org,
        linux-kernel@...r.kernel.org
Subject: Re: Kernel build with gcc 8 a lot of warnings

On Sun, May 06, 2018 at 11:54:53PM -0500, Josh Poimboeuf wrote:
> On Sat, May 05, 2018 at 09:21:12PM +0200, damian wrote:
> > Helllo together,
> > 
> > Hello everybody,
> > 
> > is something special to note when kernel build with gcc 8? I receive various warnings from the objtool:
> > With GCC 7 works all fine.
> > 
> > kernel/cgroup/cgroup.o: warning: objtool: parse_cgroup_root_flags()+0x40: sibling call from callable instruction with modified stack frame
> > kernel/cgroup/cgroup.o: warning: objtool: cgroup_addrm_files()+0x2a3: sibling call from callable instruction with modified stack frame
> > kernel/cgroup/cgroup.o: warning: objtool: cgroup_apply_control_enable()+0x20b: sibling call from callable instruction with modified stack frame
> > kernel/cgroup/cgroup.o: warning: objtool: rebind_subsystems()+0x296: sibling call from callable instruction with modified stack frame
> > kernel/cgroup/cgroup.o: warning: objtool: cgroup_sk_alloc_disable()+0x10: sibling call from callable instruction with modified stack frame
> > kernel/cgroup/cgroup.o: warning: objtool: parse_cgroup_root_flags.cold.45()+0xa: call without frame pointer save/setup
> > kernel/cgroup/cgroup.o: warning: objtool: cgroup_addrm_files.cold.46()+0x17: call without frame pointer save/setup
> > kernel/cgroup/cgroup.o: warning: objtool: cgroup_apply_control_enable.cold.47()+0x24: call without frame pointer save/setup
> > kernel/cgroup/cgroup.o: warning: objtool: rebind_subsystems.cold.48()+0x10: call without frame pointer save/setup
> > kernel/cgroup/cgroup.o: warning: objtool: cgroup_sk_alloc_disable.cold.49()+0x7: call without frame pointer save/setup
> >   CC      kernel/cgroup/stat.o
> >   CC [M]  arch/x86/kvm/../../../virt/kvm/kvm_main.o
> > arch/x86/kernel/acpi/boot.o: warning: objtool: acpi_register_lapic()+0x10: sibling call from callable instruction with modified stack frame
> > arch/x86/kernel/acpi/boot.o: warning: objtool: acpi_map_cpu()+0x2c: sibling call from callable instruction with modified stack frame
> > arch/x86/kernel/acpi/boot.o: warning: objtool: acpi_register_lapic.cold.6()+0x7: call without frame pointer save/setup
> > arch/x86/kernel/acpi/boot.o: warning: objtool: acpi_map_cpu.cold.7()+0x7: call without frame pointer save/setup
> 
> Thanks, this is a known issue with GCC 8 that I haven't gotten a chance
> to fix yet.  They're related to the fact that GCC 8 is splitting out
> 'unlikely' code into 'cold' subfunctions in .text.unlikely.
> 
> I've got some old patches that fix it.  Now that GCC 8 is out, I'll need
> get the patches dusted off and cleaned up for merging.

Any pointers to these patches?  Archi linux just changed their default
compiler to gcc 8 and now I'm seeing this in my local builds :(

thanks,

greg k-h