linux-kernel - Re: libelf-0.175 breaks objtool

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Message-ID: <20200406221614.ac2kl3vlagiaj5jf@treble>
Date:   Mon, 6 Apr 2020 17:16:14 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: libelf-0.175 breaks objtool

On Mon, Apr 06, 2020 at 11:07:15PM +0200, Arnd Bergmann wrote:
> On Wed, Feb 6, 2019 at 7:32 PM Steven Rostedt <rostedt@...dmis.org> wrote:
> > On Tue, 5 Feb 2019 20:16:11 -0600 Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >
> > > On Tue, Feb 05, 2019 at 01:38:21PM -0500, Steven Rostedt wrote:
> > > > Just a FYI.
> > > >
> > > > After a recent upgrade in debian testing, I was not able to build the
> > > > kernel. I have a custom build of gcc, so I thought it was strange that
> > > > I was getting something like this (took this from the web, as I don't
> > > > have the error anymore with the work around, and currently doing a full
> > > > build):
> > > >
> > > > objdump: kernel/.tmp_signal.o: unable to initialize decompress status for section .debug_info
> > > > objdump: kernel/.tmp_signal.o: unable to initialize decompress status for section .debug_info
> > > > objdump: kernel/.tmp_signal.o: file format not recognized
> > > >   CC      arch/x86/kernel/platform-quirks.o
> > > > objdump: arch/x86/kernel/.tmp_ebda.o: unable to initialize decompress status for section .debug_info
> > > > objdump: arch/x86/kernel/.tmp_ebda.o: unable to initialize decompress status for section .debug_info
> > > > objdump: arch/x86/kernel/.tmp_ebda.o: file format not recognized
> > > > objdump: mm/.tmp_swap_slots.o: unable to initialize decompress status for section .debug_info
> > > > objdump: mm/.tmp_swap_slots.o: unable to initialize decompress status for section .debug_info
> > > > objdump: mm/.tmp_swap_slots.o: file format not recognized
> > >
> > > I installed debian testing on a VM, which has libelf 0.175-2, but I
> >
> > Hmm, I only have libelf-0.175 (no -2)
> >
> > > can't recreate.  Can you share your config?
> > >
> >
> > It's just a distro config. Ah, I think it's because I'm compiling my
> > own home built gcc. There seems to be an incompatibility with the
> > binutils that I used and with libelf-0.175. If I build with just the
> > distro gcc, it works.
> >
> > Bah, this means I need to recreate my gcc that I use to build my
> > kernels with :-p As I like to control which gcc I use.
> 
> I now see the same problem that you reported using the gcc-9
> toolchain I provide on https://kernel.org/pub/tools/crosstool/.
> 
> Do you have any other information that might help me fix it?

This sounds like an issue I saw before where the toolchain wants to
compress debuginfo (DWARF debug_info sections).  The "fix" was to add
'-gz=none' to KCFLAGS.

But if it's a desired feature then we could probably teach objtool to
deal with it.  It ignores DWARF anyway.

-- 
Josh