linux-kernel - Re: [syzbot] upstream build error (23)

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Message-ID: <CAHk-=wirbb_FxAMsb+LFimsMF+nLg4UYsrHvjF1F9tF1xOm2UA@mail.gmail.com>
Date: Tue, 29 Jul 2025 14:38:50 -0700
From: Linus Torvalds <torvalds@...uxfoundation.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: syzbot <syzbot+5245cb609175fb6e8122@...kaller.appspotmail.com>, bp@...en8.de, 
	dave.hansen@...ux.intel.com, hpa@...or.com, linux-kernel@...r.kernel.org, 
	mingo@...hat.com, syzkaller-bugs@...glegroups.com, x86@...nel.org, 
	Kees Cook <kees@...nel.org>
Subject: Re: [syzbot] upstream build error (23)

On Tue, 29 Jul 2025 at 14:17, Thomas Gleixner <tglx@...utronix.de> wrote:
>
> Can we just stop pretending that GCC12 is KCOV capable?

Yeah, that does seem to be the right thing to do. KCOV just isn't
important enough to

 (a) play constant whack-a-mole with

 (b) pretend we support broken compilers for

and people who want KCOV can damn well get a fixed compiler.

We already have *some* amount of compiler dependency there, since KCOV has this:

        depends on !ARCH_WANTS_NO_INSTR || HAVE_NOINSTR_HACK || \
                   GCC_VERSION >= 120000 || CC_IS_CLANG

but clearly that allows for gcc-12 - and allows for other versions too
for that NOINSTR thing.

And x86 sets "HAVE_NOINSTR_HACK" because of some argument that objtool
fixes whatever problems there were.

So it's not just about changing that GCC_VERSION number - there's some
interaction with other crazy KCOV hacks, in particular I think the
whole NOINSTR hack is about 0f1441b44e82 ("objtool: Fix noinstr vs
KCOV")

I'd personally be perfectly happy just saying "gcc-13 is required" and
presumably that allows just removing the NOINSTR_HACK thing too.

But I would want somebody to test that and verify that gcc-13 really does do ok.

              Linus