From: Sami Tolvanen <samitolvanen@google.com>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Arnd Bergmann <arnd@kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Jason Baron <jbaron@akamai.com>, Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Ard Biesheuvel <ardb@kernel.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Frederic Weisbecker <frederic@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] static_call: fix function type mismatch
Date: Wed, 24 Mar 2021 09:01:27 -0700 [thread overview]
Message-ID: <CABCJKuf1-GWda9_BiBO=nNP_drh3a8471G+LEqPzdVrLBhVqZQ@mail.gmail.com> (raw)
In-Reply-To: <0f4679d6-44a4-d045-f249-a9cffb126fd4@rasmusvillemoes.dk>
On Wed, Mar 24, 2021 at 5:46 AM Rasmus Villemoes
<linux@rasmusvillemoes.dk> wrote:
>
> On 23/03/2021 08.47, Peter Zijlstra wrote:
> > On Mon, Mar 22, 2021 at 05:29:21PM -0400, Steven Rostedt wrote:
> >> On Mon, 22 Mar 2021 22:18:17 +0100
> >> Arnd Bergmann <arnd@kernel.org> wrote:
> >>
> >>> I think the code works correctly on all architectures we support because
> >>> both 'int' and 'long' are returned in a register with any unused bits cleared.
> >>> It is however undefined behavior in C because 'int' and 'long' are not
> >>> compatible types, and the calling conventions don't have to allow this.
> >>
> >> Static calls (and so do tracepoints) currently rely on these kind of
> >> "undefined behavior" in C. This isn't the only UB that it relies on.
> >
> > Right, most of the kernel lives in UB. That's what we have -fwrapv
> > -fno-strict-aliassing and lots of other bits for, to 'fix' the stupid C
> > standard.
> >
> > This is one more of them, so just ignore the warning and make it go
> > away:
> >
> > -Wno-cast-function-type
> >
> > seems to be the magic knob.
> >
>
> That can be done for now, but I think something has to be done if CFI is
> to become a thing.
>
> Sami, what happens if you try to boot a
> CONFIG_CFI_CLANG+CONFIG_PREEMPT_DYNAMIC kernel?
Seems to boot just fine. CFI instrumentation is only for
compiler-generated indirect calls. Casting functions to different
types is fine as long as you don't end up calling them using an
incorrect pointer type.
Sami
next prev parent reply other threads:[~2021-03-24 16:02 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-22 17:06 [PATCH] static_call: fix function type mismatch Arnd Bergmann
2021-03-22 19:32 ` Steven Rostedt
2021-03-22 20:47 ` Peter Zijlstra
2021-03-22 21:18 ` Arnd Bergmann
2021-03-22 21:29 ` Steven Rostedt
2021-03-23 7:47 ` Peter Zijlstra
2021-03-24 12:46 ` Rasmus Villemoes
2021-03-24 16:01 ` Sami Tolvanen [this message]
2021-03-24 16:45 ` Rasmus Villemoes
2021-03-24 17:33 ` Peter Zijlstra
2021-03-24 19:16 ` Peter Zijlstra
2021-03-24 21:51 ` Rasmus Villemoes
2021-03-24 22:34 ` Sami Tolvanen
2021-03-24 22:53 ` Rasmus Villemoes
2021-03-24 23:40 ` Sami Tolvanen
2021-03-25 0:42 ` Rasmus Villemoes
2021-03-25 7:42 ` Peter Zijlstra
2021-03-25 7:45 ` Ard Biesheuvel
2021-03-25 8:27 ` Rasmus Villemoes
2021-03-23 7:35 ` Peter Zijlstra
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