From: Justin Forbes <jforbes@redhat.com>
To: Greg KH <greg@kroah.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Masahiro Yamada <masahiroy@kernel.org>,
Kees Cook <keescook@chromium.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Michal Marek <michal.lkml@markovi.net>,
linux-hardening@vger.kernel.org,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
Ondrej Mosnacek <omosnace@redhat.com>
Subject: Re: [PATCH RFC] gcc-plugins: Handle GCC version mismatch for OOT modules
Date: Tue, 26 Jan 2021 11:47:13 -0600 [thread overview]
Message-ID: <CAFbkSA2do8hyh8hwyA5f+GTstcv561UePu-msxPuKXN3+No_Rg@mail.gmail.com> (raw)
In-Reply-To: <YBBML2eB/IXcTvcn@kroah.com>
On Tue, Jan 26, 2021 at 11:07 AM Greg KH <greg@kroah.com> wrote:
>
> On Tue, Jan 26, 2021 at 10:19:34AM -0600, Josh Poimboeuf wrote:
> > On Tue, Jan 26, 2021 at 10:15:52AM -0600, Justin Forbes wrote:
> > > On Tue, Jan 26, 2021 at 10:05 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > > >
> > > > On Tue, Jan 26, 2021 at 09:46:51AM -0600, Josh Poimboeuf wrote:
> > > > > On Tue, Jan 26, 2021 at 04:15:37PM +0100, Peter Zijlstra wrote:
> > > > > > On Tue, Jan 26, 2021 at 08:51:55AM -0600, Josh Poimboeuf wrote:
> > > > > > > User space mixes compiler versions all the time. The C ABI is stable.
> > > > > > >
> > > > > > > What specifically is the harder issue you're referring to?
> > > > > >
> > > > > > I don't think the C ABI captures nearly enough. Imagine trying to mix a
> > > > > > compiler with and without asm-goto support (ok, we fail to build without
> > > > > > by now, but just imagine).
> > > > > >
> > > > > > No C ABI violated, but having that GCC extention vs not having it
> > > > > > radically changes the kernel ABI.
> > > > > >
> > > > > > I think I'm with Greg here, just don't do it.
> > > > >
> > > > > Ok, thank you for an actual example. asm goto is a good one.
> > > > >
> > > > > But it's not a cut-and-dry issue. Otherwise how could modversions
> > > > > possibly work?
> > > > >
> > > > > So yes, we should enforce GCC versions, but I still haven't seen a
> > > > > reason it should be more than just "same compiler and *major* version".
> > > >
> > > > Why bother? rebuilding the kernel and all modules is a matter of 10
> > > > minutes at most on a decently beefy build box.
> > > >
> > > > What actual problem are we trying to solve here?
> > >
> > > This is true for those of us used to working with source and building
> > > by hand. For users who want everything packaged, rebuilding a kernel
> > > package for install is considerably longer, and for distros providing
> > > builds for multiple arches, we are looking at a couple of hours at
> > > best. From a Fedora standpoint, I am perfectly fine with it failing
> > > if someone tries to build a module on gcc10 when the kernel was built
> > > with gcc11. It's tedious when the kernel was built with gcc11
> > > yesterday, and a new gcc11 build today means that kernel needs to be
> > > rebuilt.
> >
> > Right. It's a problem for distro users. The compiler and kernel are in
> > separate packages, with separate release cadences. The latest compiler
> > version may not exactly match what was used to build the latest kernel.
>
> Given that distros _should_ be updating their kernel faster than the
> compiler updates, what's the real issue here? You build a kernel, and
> all external modules, at the same time. If you want to build them at
> different times, you make your build system ensure they were the same
> compiler so that you are "bug compatible".
>
> And yes, it might be a pain if gcc11 gets updated every other day, but
> as someone living with a "rolling-distro" you get used to it, otherwise
> you just "pin" the build tools and keep that from happening.
>
> This isn't a new thing, we've been doing this for decades, why is this
> surprising?
We definitely build considerably more kernels than toolchains. From a
rawhide standpoint though, a number of testers are willing to test RC
releases, but are not willing to run debug kernels, so they installed
rc4 yesterday, but will not install today's snapshot. I will build
3-5 new kernels before they update to rc5. We have been doing things
this way for over a decade. It has never been a problem until we
turned on CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL. Suddenly I am
getting complaints.
next prev parent reply other threads:[~2021-01-26 18:15 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 20:42 [PATCH RFC] gcc-plugins: Handle GCC version mismatch for OOT modules Josh Poimboeuf
2021-01-25 21:16 ` Masahiro Yamada
2021-01-25 21:27 ` Josh Poimboeuf
2021-01-25 21:44 ` Masahiro Yamada
2021-01-25 22:07 ` Josh Poimboeuf
2021-01-26 8:13 ` Greg KH
2021-01-26 12:44 ` Justin Forbes
2021-01-26 13:51 ` Greg KH
2021-01-26 14:51 ` Josh Poimboeuf
2021-01-26 15:00 ` Greg KH
2021-01-26 15:15 ` Peter Zijlstra
2021-01-26 15:46 ` Josh Poimboeuf
2021-01-26 16:05 ` Peter Zijlstra
2021-01-26 16:15 ` Justin Forbes
2021-01-26 16:19 ` Josh Poimboeuf
2021-01-26 17:06 ` Greg KH
2021-01-26 17:47 ` Justin Forbes [this message]
2021-01-26 16:22 ` David Laight
2021-01-27 18:03 ` Christoph Hellwig
2021-01-26 8:12 ` Greg KH
2021-01-25 22:03 ` Kees Cook
2021-01-25 22:19 ` Josh Poimboeuf
2021-01-26 17:56 ` Kees Cook
2021-01-26 18:43 ` Josh Poimboeuf
2021-01-26 22:59 ` Kees Cook
2021-01-26 23:32 ` Josh Poimboeuf
2021-01-26 1:53 ` Masahiro Yamada
2021-01-26 12:16 ` David Laight
2021-01-27 18:02 ` Christoph Hellwig
2021-01-27 18:38 ` Josh Poimboeuf
2021-01-27 18:43 ` Christoph Hellwig
2021-01-27 18:51 ` Josh Poimboeuf
2021-01-27 22:09 ` David Laight
2021-01-28 14:29 ` Christoph Hellwig
2021-01-28 15:45 ` Josh Poimboeuf
2021-03-02 23:26 ` Josh Poimboeuf
2021-03-03 18:49 ` Masahiro Yamada
2021-03-03 19:15 ` Josh Poimboeuf
2021-03-03 19:25 ` Linus Torvalds
2021-03-03 19:38 ` Josh Poimboeuf
2021-03-03 19:57 ` Linus Torvalds
2021-03-03 20:24 ` Josh Poimboeuf
2021-03-03 20:31 ` Josh Poimboeuf
2021-03-03 20:56 ` Linus Torvalds
2021-03-03 21:45 ` Josh Poimboeuf
2021-03-04 12:27 ` Masahiro Yamada
2021-03-04 15:08 ` Josh Poimboeuf
2021-03-04 15:35 ` Masahiro Yamada
2021-03-04 19:12 ` Linus Torvalds
2021-03-05 2:41 ` Josh Poimboeuf
2021-03-05 2:49 ` Linus Torvalds
2021-03-05 16:03 ` Masahiro Yamada
2021-03-05 19:18 ` Josh Poimboeuf
2021-03-08 9:39 ` David Laight
2021-03-05 15:31 ` Masahiro Yamada
2021-03-03 21:52 ` Kees Cook
2021-03-04 12:26 ` Masahiro Yamada
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