linux-kernel - Re: [PATCH v2 4/5] efi/x86: Remove extra headroom for setup block

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Message-ID: <20200511225324.GA1307788@rani.riverdale.lan>
Date:   Mon, 11 May 2020 18:53:24 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Mike Lothian <mike@...eburn.co.uk>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>
Subject: Re: [PATCH v2 4/5] efi/x86: Remove extra headroom for setup block

On Mon, May 11, 2020 at 11:13:00PM +0200, Ard Biesheuvel wrote:
> On Mon, 11 May 2020 at 20:36, Arvind Sankar <nivedita@...m.mit.edu> wrote:
> >
> > On Mon, May 11, 2020 at 06:01:49PM +0100, Mike Lothian wrote:
> > > Hi
> > >
> > > This patch has been causing issues for me since switching to GCC 10.1:
> > >
> > >   CALL    scripts/checksyscalls.sh
> > >   CALL    scripts/atomic/check-atomics.sh
> > >   DESCEND  objtool
> > >   CHK     include/generated/compile.h
> > >   HOSTCC  arch/x86/boot/tools/build
> > > /usr/lib/gcc/x86_64-pc-linux-gnu/10.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: error: linker defined: multiple definition of '_end'
> > > /usr/lib/gcc/x86_64-pc-linux-gnu/10.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: /tmp/ccEkW0jM.o: previous definition here
> > > collect2: error: ld returned 1 exit status
> > > make[1]: *** [scripts/Makefile.host:103: arch/x86/boot/tools/build] Error 1
> > > make: *** [arch/x86/Makefile:303: bzImage] Error 2
> > >
> > > Cheers
> > >
> > > Mike
> >
> > I'm not getting an error even with gcc 10 for some reason, but I can see
> > that it is busted. It's using the linker-defined _end symbol which is
> > just pass the end of the .bss.
> >
> > Does adding "static" to the declaration of _end fix your error?
> 
> This is in a host tool, so it depends on the builtin linker script the
> toolchain decides to use. This is risky, though, as it may be using
> PROVIDE() for _end, which means that in cases where it doesn't break,
> other references to _end that may exist will be linked to the wrong
> symbol. I don't think 'build' should be expected to do anything
> interesting with its own representation in memory, but better fix it
> nonetheless.

Right, _end _is_ getting redefined in my system linker script too: I can
see with objdump that the final _end symbol in my version of build is
actually pointing beyond the .bss. But my toolchain doesn't report an
error for some reason.

> 
> Arvind: mind sending a fix for this, please?

Yeah, I have one ready -- was just waiting to hear back if "static" did
fix it, but I can send it out now.