linux-kernel - Re: Large modules with 6.15 [was: [PATCH v4 6/6] percpu/x86: Enable strict percpu checks via named AS qualifiers]

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Message-ID: <CAFULd4Ygz8p8rD1=c-S2MjJniP6vjVNMsWG_B=OjCVpthk0fBg@mail.gmail.com>
Date: Thu, 5 Jun 2025 19:31:44 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Jiri Slaby <jirislaby@...nel.org>, x86@...nel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, linux-bcachefs@...r.kernel.org, 
	linux-arch@...r.kernel.org, netdev@...r.kernel.org, 
	Nadav Amit <nadav.amit@...il.com>, Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, 
	Christoph Lameter <cl@...ux.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	"H. Peter Anvin" <hpa@...or.com>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Andy Lutomirski <luto@...nel.org>, Brian Gerst <brgerst@...il.com>, 
	Peter Zijlstra <peterz@...radead.org>, Shung-Hsi Yu <shung-hsi.yu@...e.com>
Subject: Re: Large modules with 6.15 [was: [PATCH v4 6/6] percpu/x86: Enable
 strict percpu checks via named AS qualifiers]

On Thu, Jun 5, 2025 at 7:15 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 6/5/25 07:27, Jiri Slaby wrote:
> > Reverting this gives me back to normal sizes.
> >
> > Any ideas?
>
> I don't see any reason not to revert it. The benefits weren't exactly
> clear from the changelogs or cover letter. Enabling "various compiler
> checks" doesn't exactly scream that this is critical to end users in
> some way.
>
> The only question is if we revert just this last patch or the whole series.
>
> Uros, is there an alternative to reverting?

This functionality can easily be disabled in include/linux/compiler.h
by not defining USE_TYPEOF_UNQUAL:

#if CC_HAS_TYPEOF_UNQUAL && !defined(__CHECKER__)
# define USE_TYPEOF_UNQUAL 1
#endif

(support for typeof_unqual keyword is required to handle __seg_gs
qualifiers), but ...

... the issue is reportedly fixed, please see [1], and ...

... you will disable much sought of feature, just ask tglx (and please
read his rant at [2]):

--q--
If the compiler people would have provided a way to utilize the anyway
non-standard name space support in a useful way, I could have spared the
time to bang my head agaist the wall simply because this would have failed
to build in the first place long ago. That just makes me sad.
--/q--

[1] https://lore.kernel.org/bpf/20250429161042.2069678-1-alan.maguire@oracle.com/
[2] https://lore.kernel.org/lkml/20240303235029.555787150@linutronix.de/

Uros.