linux-kernel - RE: Compile problems w/gcc 9.4.0 in linux-next

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Message-ID:
 <SN6PR02MB41575C4BA0C467B1C95EEB21D4D82@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Thu, 20 Mar 2025 21:58:37 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Michael Kelley <mhklinux@...look.com>, Ard Biesheuvel <ardb@...nel.org>,
	"terrelln@...com" <terrelln@...com>, "dsterba@...e.com" <dsterba@...e.com>
CC: "brgerst@...il.com" <brgerst@...il.com>, "mingo@...nel.org"
	<mingo@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: Compile problems w/gcc 9.4.0 in linux-next

From: Michael Kelley <mhklinux@...look.com> Sent: Thursday, March 20, 2025 1:42 PM
> 
> From: Ard Biesheuvel <ardb@...nel.org> Sent: Thursday, March 20, 2025 12:20 PM
> >
> > Hi Michael,
> >
> > On Thu, 20 Mar 2025 at 19:29, Michael Kelley <mhklinux@...look.com> wrote:
> > >
> > > Brian/Ingo/Ard -
> > >
> > > I'm seeing a compile problem in linux-next-20250319 with gcc 9.4.0. I've bisected
> > > to a group of 6 commits that you authored:
> > >
> > > a9a76b38aaf5 x86/boot: Disable stack protector for early boot code
> > > f58b63857ae3 x86/pvh: Use fixed_percpu_data for early boot GSBASE
> > > cb7927fda002 x86/relocs: Handle R_X86_64_REX_GOTPCRELX relocations
> > > 78c4374ef8b8 x86/module: Deal with GOT based stack cookie load on Clang < 17
> > > 80d47defddc0 x86/stackprotector/64: Convert to normal per-CPU variable
> > > 9d7de2aa8b41 x86/percpu/64: Use relative percpu offsets
> > >
> > > As of a9a76b38aaf5, everything compiles correctly.
> > >
> > > For f58b63857ae3 thru 80d47defddc0, this error occurs:
> > >
> > >     arch/x86/platform/pvh/head.S: Assembler messages:
> > >     arch/x86/platform/pvh/head.S:183: Error: operand size mismatch for `movq'
> > >
> >
> > This is simply a bug in patch f58b63857ae3, which uses movq on
> > EDX/EAX. This breaks bisection (as you've noticed), annoyingly, and
> > I'll leave it to the tip maintainers to decide whether this warrants a
> > rebase (given that the fix is already queued up as well)
> >
> > > As of 9d7de2aa8b41 and later, the head.S error goes away, and this
> > > error occurs:
> > >
> > >     lib/zstd/compress/huf_compress.c:1033:1: internal compiler error: Segmentation fault
> > >      1033 | {
> > >           | ^
> > >     Please submit a full bug report,
> > >     with preprocessed source if appropriate.
> > >     See <file:///usr/share/doc/gcc-9/README.Bugs> for instructions.
> > >
> > > Interestingly, if DYNAMIC_BMI2 in lib/zstd/common/portability_macros.h
> > > is changed on line 61 to always be defined as 0, the compile problem in
> > > huf_compress.c goes away.
> > >
> >
> > Without having looked at the crashing code, I suspect that the only
> > meaningful course of action here is to tweak the conditional logic
> > that defines DYNAMIC_BMI2 to only enable it for GCC >= 10.1 (assuming
> > those are unaffected) In any case, GCC 9.4 is not going to get fixed
> > in the field, so even if this gets fixed on the GCC side, we will have
> > to deal with it here.
> 
> Nick and David --
> 
> What are your thoughts as maintainers of lib/zstd?
> 

FYI, the same segfault occurs with gcc 10.5. The problem is fixed
in gcc 11.4.

Michael

> 
> >
> > > I'm using gcc 9.4.0 in an Ubuntu 20.04 install as it's the standard compiler
> > > for that version of Ubuntu. I'm guessing that getting a fix for that
> > > relatively old version of gcc isn't likely. I have not tested with other
> > > gcc versions.