linux-kernel - Re: [PATCH RFC] riscv: Allow to build only with LLVM >= 17.0.0

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Message-ID: <20240717-commuting-channel-4ad202950e4c@spud>
Date: Wed, 17 Jul 2024 14:06:42 +0100
From: Conor Dooley <conor@...nel.org>
To: Alexandre Ghiti <alex@...ti.fr>
Cc: Alexandre Ghiti <alexghiti@...osinc.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Björn Töpel <bjorn@...osinc.com>,
	Conor Dooley <conor.dooley@...rochip.com>,
	Nathan Chancellor <nathan@...nel.org>, linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH RFC] riscv: Allow to build only with LLVM >= 17.0.0

On Wed, Jul 17, 2024 at 01:06:39PM +0100, Conor Dooley wrote:
> On Wed, Jul 17, 2024 at 01:41:23PM +0200, Alexandre Ghiti wrote:
> > Hi Conor,
> > 
> > On 17/07/2024 13:32, Conor Dooley wrote:
> > > On Wed, Jul 17, 2024 at 01:17:16PM +0200, Alexandre Ghiti wrote:
> > > > The following build failure happens when using LLVM < 17.0.0:
> > > > 
> > > > kernel/sched/core.c:11873:7: error: cannot jump from this asm goto statement to one of its possible targets
> > > > 
> > > > This is a known issue [1] so let's upgrade the minimal requirement for
> > > > LLVM to the version 17.0.0, which is the first version to contain the
> > > > fix.
> > > I think doing this unilaterally is kinda insane, LLVM 17 isn't even a
> > > year old. Debian testing doesn't have anything later than 16.
> > 
> > 
> > Debian will very likely select the qspinlocks when available anyway, so
> > they'll need llvm >= 17. And Debian won't ship a kernel >= 6.11 until some
> > time right? So they'll probably update their infra to llvm >= 17 (and
> > they'll probably do to take advantages of the new extensions).
> 
> What I mean is that you are going to prevent people building the kernel
> with llvm on machines running anything but very recent rolling-release
> distros. Your patch would stop most developers, including those who don't
> care about your qspinlock stuff, even build testing with the version of
> LLVM that their distro provides. I'm not talking about distros building
> kernels in their build infrastructure.
> 
> > 
> > 
> > > Why does
> > > it need to be done unilaterally rather than just when the qspinlock
> > > stuff is built?
> > 
> > 
> > We can do that indeed, it may happen again and we can keep requiring llvm 17
> > on a per-config basis.

Nathan pointed out to me that I misunderstood the build failure, and
that it happens whether or not the option is enabled. /sigh.

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