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Date:   Wed, 5 Jun 2019 21:26:06 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Rolf Eike Beer <eb@...ix.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: Building arm64 EFI stub with -fpie breaks build of 4.9.x
 (undefined reference to `__efistub__GLOBAL_OFFSET_TABLE_')

On Wed, Jun 05, 2019 at 08:42:32PM +0200, Ard Biesheuvel wrote:
> On Wed, 5 Jun 2019 at 18:26, Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Wed, Jun 05, 2019 at 05:19:40PM +0200, Rolf Eike Beer wrote:
> > > I decided to dig out a toy project which uses a DragonBoard 410c. This has
> > > been "running" with kernel 4.9, which I would keep this way for unrelated
> > > reasons. The vanilla 4.9 kernel wasn't bootable back then, but it was
> > > buildable, which was good enough.
> > >
> > > Upgrading the kernel to 4.9.180 caused the boot to suddenly fail:
> > >
> > > aarch64-unknown-linux-gnueabi-ld: ./drivers/firmware/efi/libstub/lib.a(arm64-
> > > stub.stub.o): in function `handle_kernel_image':
> > > /tmp/e2/build/linux-4.9.139/drivers/firmware/efi/libstub/arm64-stub.c:63:
> > > undefined reference to `__efistub__GLOBAL_OFFSET_TABLE_'
> > > aarch64-unknown-linux-gnueabi-ld: ./drivers/firmware/efi/libstub/lib.a(arm64-
> > > stub.stub.o): relocation R_AARCH64_ADR_PREL_PG_HI21 against symbol
> > > `__efistub__GLOBAL_OFFSET_TABLE_' which may bind externally can not be used
> > > when making a shared object; recompile with -fPIC
> > > /tmp/e2/build/linux-4.9.139/drivers/firmware/efi/libstub/arm64-stub.c:63:
> > > (.init.text+0xc): dangerous relocation: unsupported relocation
> > > /tmp/e2/build/linux-4.9.139/Makefile:1001: recipe for target 'vmlinux' failed
> > > -make[1]: *** [vmlinux] Error 1
> > >
> > > This is caused by commit 27b5ebf61818749b3568354c64a8ec2d9cd5ecca from
> > > linux-4.9.y (which is 91ee5b21ee026c49e4e7483de69b55b8b47042be), reverting
> > > this commit fixes the build.
> > >
> > > This happens with vanilla binutils 2.32 and gcc 8.3.0 as well as 9.1.0. See
> > > the attached .config for reference.
> > >
> > > If you have questions or patches just ping me.
> >
> > Does Linus's latest tree also fail for you (or 5.1)?
> >
> > Nick, do we need to add another fix that is in mainline for this to work
> > properly?
> >
> 
> For the record, this is an example of why I think backporting those
> clang enablement patches is a bad idea. We can't actually build those
> kernels with clang, can we? So what is the point? </grumpy>

Yes "we" can.  I do.  Why can't you?

And lots of devices rely on clang support for their kernels, as much as
I would like to ignore them, I can't :(

thanks,

greg k-h

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