linux-kernel - Re: [PATCH] x86/tools/relocs: Add _etext and __end_of_kernel_reserve to S

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Date:   Mon, 13 Jan 2020 18:38:29 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Thomas Lendacky <Thomas.Lendacky@....com>
Subject: Re: [PATCH] x86/tools/relocs: Add _etext and __end_of_kernel_reserve
 to S_REL

On Sat, Jan 11, 2020 at 02:02:43PM +0100, Borislav Petkov wrote:
> On Fri, Jan 10, 2020 at 03:50:29PM -0500, Arvind Sankar wrote:
> > On Fri, Jan 10, 2020 at 09:38:28PM +0100, Borislav Petkov wrote:
> > > On Fri, Jan 10, 2020 at 03:23:49PM -0500, Arvind Sankar wrote:
> > > > Pre-2.23 binutils makes symbols defined outside sections absolute, so
> > > > these two symbols break the build on old linkers.
> > > 
> > > -ENOTENOUGHINFO
> > > 
> > > Which old linkers, how exactly do they break the build, etc etc?
> > > 
> > > Please give exact reproduction steps.
> > > 
> > > Thx.
> > > 
> > 
> > binutils-2.21 and -2.22. An x86-64 defconfig will fail with
> > 	Invalid absolute R_X86_64_32S relocation: _etext
> > and after fixing that one, with
> > 	Invalid absolute R_X86_64_32S relocation: __end_of_kernel_reserve
> 
> I'm still not clear as to why this happens. I tried reproducing on
> openSUSE 12.1 which has
> 
> Repository: openSUSE-12.1-Oss
> Name: binutils
> Version: 2.21.1-12.1.4
> 
> and the build there fails with:
> 
> objdump: arch/x86/lib/clear_page_64.o: File format not recognized
> objdump: arch/x86/lib/cmdline.o: File format not recognized
> objdump: arch/x86/lib/cmpxchg16b_emu.o: File format not recognized
> objdump: arch/x86/lib/copy_page_64.o: File format not recognized
> objdump: arch/x86/lib/copy_user_64.o: File format not recognized
> objdump: arch/x86/lib/cpu.o: File format not recognized
> ...
> 
> and objdump is part of binutils.
> 
> Now, this looks like another symptom of what you're reporting but what
> we're missing is the rootcause about *why* this happens.

I tried out OpenSUSE 12.1 in a VM, and this one seems to be related to
something that changes in the build when libelf-devel is installed.
Deleting that package and switching UNWINDER_ORC (which says it requires
libelf-devel) to UNWINDER_FRAME_POINTER builds without the file format
errors.

> 
> Because if the issue is hard to fix or similar, then we probably should
> raise the minimum supported binutils version from 2.21 to something
> newer and not do this fix.
> 
> But before we do that, we need a proper analysis as to why it happens.
> 
> Also, what distro are you using to reproduce it on?
> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette