linux-kernel - RE: [PATCH v2] hexagon: Disable constant extender optimization for LLVM prior to 19.1.0

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Message-ID:
 <DS0PR02MB102502302B8074AFA8BB1BAFEB8052@DS0PR02MB10250.namprd02.prod.outlook.com>
Date: Wed, 18 Dec 2024 02:11:07 +0000
From: Brian Cain <bcain@...cinc.com>
To: Nathan Chancellor <nathan@...nel.org>,
        Andrew Morton
	<akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC: "linux-hexagon@...r.kernel.org" <linux-hexagon@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        "llvm@...ts.linux.dev"
	<llvm@...ts.linux.dev>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] hexagon: Disable constant extender optimization for
 LLVM prior to 19.1.0

> -----Original Message-----
> From: Nathan Chancellor <nathan@...nel.org>
> Sent: Tuesday, December 17, 2024 11:44 AM
> To: Brian Cain <bcain@...cinc.com>; Andrew Morton <akpm@...ux-
> foundation.org>; Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: linux-hexagon@...r.kernel.org; patches@...ts.linux.dev;
> llvm@...ts.linux.dev; stable@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v2] hexagon: Disable constant extender optimization for
> LLVM prior to 19.1.0
> 
> 
> Hi Linus,
> 
> Could you apply this change [1] directly? Brian has reviewed it and I have
> sent this patch twice plus another ping for application [2]. I would
> like to stop applying this in our CI and some other people have hit it
> as well.

Nathan,

I'm sorry.  You should not have to send these changes to Linus. I should have carried it in my tree and proposed it to Linus.

I'll do that, if you don't mind.

> [1]: https://lore.kernel.org/all/20241121-hexagon-disable-constant-
> expander-pass-v2-1-1a92e9afb0f4@...nel.org/
> [2]: https://lore.kernel.org/all/20241001185848.GA562711@thelio-3990X/
> 
> Cheers,
> Nathan
> 
> On Thu, Nov 21, 2024 at 11:22:18AM -0700, Nathan Chancellor wrote:
> > The Hexagon-specific constant extender optimization in LLVM may crash on
> > Linux kernel code [1], such as fs/bcache/btree_io.c after
> > commit 32ed4a620c54 ("bcachefs: Btree path tracepoints") in 6.12:
> >
> >   clang: llvm/lib/Target/Hexagon/HexagonConstExtenders.cpp:745: bool
> (anonymous namespace)::HexagonConstExtenders::ExtRoot::operator<(const
> HCE::ExtRoot &) const: Assertion `ThisB->getParent() == OtherB->getParent()'
> failed.
> >   Stack dump:
> >   0.      Program arguments: clang --target=hexagon-linux-musl ...
> fs/bcachefs/btree_io.c
> >   1.      <eof> parser at end of file
> >   2.      Code generation
> >   3.      Running pass 'Function Pass Manager' on module
> 'fs/bcachefs/btree_io.c'.
> >   4.      Running pass 'Hexagon constant-extender optimization' on function
> '@...tree_node_lock_nopath'
> >
> > Without assertions enabled, there is just a hang during compilation.
> >
> > This has been resolved in LLVM main (20.0.0) [2] and backported to LLVM
> > 19.1.0 but the kernel supports LLVM 13.0.1 and newer, so disable the
> > constant expander optimization using the '-mllvm' option when using a
> > toolchain that is not fixed.
> >
> > Cc: stable@...r.kernel.org
> > Link: https://github.com/llvm/llvm-project/issues/99714 [1]
> > Link: https://github.com/llvm/llvm-
> project/commit/68df06a0b2998765cb0a41353fcf0919bbf57ddb [2]
> > Link: https://github.com/llvm/llvm-
> project/commit/2ab8d93061581edad3501561722ebd5632d73892 [3]
> > Reviewed-by: Brian Cain <bcain@...cinc.com>
> > Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> > ---
> > Andrew, can you please take this for 6.13? Our CI continues to hit this.
> >
> > Changes in v2:
> > - Rebase on 6.12 to make sure it is still applicable
> > - Name exact bcachefs commit that introduces crash now that it is
> >   merged
> > - Add 'Cc: stable' as this is now visible in a stable release
> > - Carry forward Brian's reviewed-by
> > - Link to v1: https://lore.kernel.org/r/20240819-hexagon-disable-constant-
> expander-pass-v1-1-36a734e9527d@...nel.org
> > ---
> >  arch/hexagon/Makefile | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/arch/hexagon/Makefile b/arch/hexagon/Makefile
> > index
> 92d005958dfb232d48a4ca843b46262a84a08eb4..ff172cbe5881a074f9d94
> 30c37071992a4c8beac 100644
> > --- a/arch/hexagon/Makefile
> > +++ b/arch/hexagon/Makefile
> > @@ -32,3 +32,9 @@ KBUILD_LDFLAGS += $(ldflags-y)
> >  TIR_NAME := r19
> >  KBUILD_CFLAGS += -ffixed-$(TIR_NAME) -
> DTHREADINFO_REG=$(TIR_NAME) -D__linux__
> >  KBUILD_AFLAGS += -DTHREADINFO_REG=$(TIR_NAME)
> > +
> > +# Disable HexagonConstExtenders pass for LLVM versions prior to 19.1.0
> > +# https://github.com/llvm/llvm-project/issues/99714
> > +ifneq ($(call clang-min-version, 190100),y)
> > +KBUILD_CFLAGS += -mllvm -hexagon-cext=false
> > +endif
> >
> > ---
> > base-commit: adc218676eef25575469234709c2d87185ca223a
> > change-id: 20240802-hexagon-disable-constant-expander-pass-
> 8b6b61db6afc
> >
> > Best regards,
> > --
> > Nathan Chancellor <nathan@...nel.org>
> >