linux-kernel - Re: Latest clang versions fail to compile CONFIG_X86_X32

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Message-ID: <CANp29Y4GGCkaW+YHAeGtvTA0XQh6c+5FaiXTvZcZtXH1D0G4WA@mail.gmail.com>
Date: Tue, 15 Apr 2025 16:40:55 +0200
From: Aleksandr Nogikh <nogikh@...gle.com>
To: Nathan Chancellor <nathan@...nel.org>, thomas.weissschuh@...utronix.de
Cc: llvm@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>, 
	syzkaller <syzkaller@...glegroups.com>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Alexander Potapenko <glider@...gle.com>
Subject: Re: Latest clang versions fail to compile CONFIG_X86_X32_ABI=y

Hi Thomas and Nathan,

Thank you for your very quick replies!
I've tried to run "make LLVM=1" instead of passing CC= and LD=, and it
worked well.

On Mon, Apr 14, 2025 at 5:16 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> On Mon, Apr 14, 2025 at 04:11:15PM +0200, Aleksandr Nogikh wrote:
> > Hi,
> >
> > I've been trying to build a Linux kernel using newer llvm toolchain
> > versions (18, 19, 20), but it consistently fails with the following
> > errors:
> >
> > ld.lld: error: arch/x86/entry/vdso/vgetrandom-x32.o:(.note.gnu.property+0x0):
> > data is too short
> > ld.lld: error: arch/x86/entry/vdso/vgetcpu-x32.o:(.note.gnu.property+0x0):
> > data is too short
> > ld.lld: error: arch/x86/entry/vdso/vclock_gettime-x32.o:(.note.gnu.property+0x0):
> > data is too short
> >
> > The steps to reproduce:
> > $ git checkout v6.15-rc2
> > $ make defconfig
> > $ ./scripts/config -e X86_X32_ABI
> > $ make CC=clang LD=ld.lld -j48
> >
> > The versions used:
> > $ clang --version
> > Debian clang version 20.1.2
> > (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97)
> > $ ld.lld --version
> > Debian LLD 20.1.2 (compatible with GNU linkers)
> >
> > Is this a known clang/Linux issue?
>
> I am not aware of this but it is likely because as Thomas pointed out,
> this invocation is only using clang/the integrated assembler and ld.lld,
> not the entire LLVM toolchain, which is generally what we encourage
> people to use unless there is a problem with doing so.
>
> > There's a kernel commit that addresses a similar problem:
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=aaeed6ecc1253ce1463fa1aca0b70a4ccbc9fa75
> >
> > but the error is slightly different there and the added Kconfig
> > condition apparently did not kick in.
>
> What version of binutils is being used here ('objcopy --version')? I can
> try and look into this and see if the Kconfig checks should be expanded
> to include other tools/versions. I highly doubt anyone building with
> LLVM would notice lack of x32 support, as I believe only Debian and
> Gentoo have support for it and some x86 folks have tried to put it on
> the chopping block before.

$ objcopy --version
GNU objcopy (GNU Binutils for Debian) 2.40

I'd say that the lack of x32 support is not a big problem by itself;
it was more of a surprise to figure out that the compilation failed
for the combination of newer clang versions + the syzbot kernel
configs. It worked well with clang-15.

We'll switch to LLVM=1, so it will hopefully prevent such problems in
the future.

-- 
Best,
Aleksandr

>
> Cheers,
> Nathan