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

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Message-ID: <Z-MovH_wFIW-xFBE@gmail.com>
Date: Tue, 25 Mar 2025 23:05:48 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Nick Terrell <terrelln@...a.com>
Cc: Michael Kelley <mhklinux@...look.com>, Ard Biesheuvel <ardb@...nel.org>,
	"dsterba@...e.com" <dsterba@...e.com>,
	"brgerst@...il.com" <brgerst@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Compile problems w/gcc 9.4.0 in linux-next


* Nick Terrell <terrelln@...a.com> wrote:

> 
> 
> > On Mar 25, 2025, at 6:18 AM, Ingo Molnar <mingo@...nel.org> wrote:
> > 
> > > 
> > 
> > * Nick Terrell <terrelln@...a.com> wrote:
> > 
> >> 
> >> 
> >>> On Mar 21, 2025, at 8:16 AM, Michael Kelley <mhklinux@...look.com> wrote:
> >>> 
> >>>> 
> >>> From: Ingo Molnar <mingo@...nel.org> Sent: Friday, March 21, 2025 12:38 AM
> >>>> 
> >>>> * Michael Kelley <mhklinux@...look.com> wrote:
> >>>> 
> >>>>>> 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.
> >>>> 
> >>>> So the patch below would work this around on GCC9 and GCC10?
> >>> 
> >>> I've confirmed that the patch gives a clean compile with gcc 9.4.
> >>> 
> >>> Note that I confirmed yesterday that the gcc problem is fixed with
> >>> 11.4. I don't know about earlier gcc 11 minor versions. Lemme see
> >>> if I can get the original gcc 11 release and try that to confirm that
> >>> your patch has the right version cutoff.
> >> 
> >> Thanks for the report & proposed fix!
> >> 
> >> If you can test gcc-11.0, that would be great, otherwise we could just
> >> cut off at (__GNUC__ >= 12 || (__GNUC__ == 11 && __GNUC_MINOR__ >= 4))
> >> 
> >> I am preparing the zstd-v1.5.7 update, and I will pull a patch that 
> >> fixes this into my tree. If someone wants to submit a patch I'll pull 
> >> that, otherwise I can submit one later today.
> > 
> > The proper cutoff would be GCC 11.1, not 11.4, as per the testing of 
> > Michael Kelley, right?
> 
> Sorry, I didn't quite realize that the [tip: x86/core] was a commit. I'll drop
> my patch, and just make sure that the fix is preserved in the zstd-v1.5.7
> upgrade.

Yeah, the segfault triggered due to changes in the x86 tree, so the fix 
(workaround) is now upstream, but I think the cutoff is overly 
conservative:

  1400c87e6cac ("zstd: Increase DYNAMIC_BMI2 GCC version cutoff from 4.8 to 11.0 to work around compiler segfault")

So it might be a good idea to follow it up with your improved cutoff 
patch, as a delta patch on top? That doesn't have any urgency that I 
can see, so it can go through your tree, or any other path you'd 
prefer!

Thanks,

	Ingo