From: Peter Zijlstra <peterz@infradead.org>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Florian Weimer <fw@deneb.enyo.de>,
Nick Desaulniers <ndesaulniers@google.com>,
Sami Tolvanen <samitolvanen@google.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Matt Mullins <mmullins@mmlx.us>, Ingo Molnar <mingo@redhat.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Dmitry Vyukov <dvyukov@google.com>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>, netdev <netdev@vger.kernel.org>,
bpf <bpf@vger.kernel.org>, Kees Cook <keescook@chromium.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
linux-toolchains@vger.kernel.org
Subject: Re: violating function pointer signature
Date: Thu, 19 Nov 2020 09:36:48 +0100 [thread overview]
Message-ID: <20201119083648.GE3121392@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20201118191127.GM2672@gate.crashing.org>
On Wed, Nov 18, 2020 at 01:11:27PM -0600, Segher Boessenkool wrote:
> Calling this via a different declared function type is undefined
> behaviour, but that is independent of how the function is *defined*.
> Your program can make ducks appear from your nose even if that function
> is never called, if you do that. Just don't do UB, not even once!
Ah, see, here I think we disagree. UB is a flaw of the spec, but the
real world often has very sane behaviour there (sometimes also very
much not).
In this particular instance the behaviour is UB because the C spec
doesn't want to pin down the calling convention, which is something I
can understand. But once you combine the C spec with the ABI(s) at hand,
there really isn't two ways about it. This has to work, under the
premise that the ABI defines a caller cleanup calling convention.
So in the view that the compiler is a glorified assembler, I'll take UB
every day if it means I can get the thing to do what I want it to.
Obviously in the interest of co-operation and longer term viability, it
would be nice if we can agree on the behaviour and get a language
extention covering it.
Note that we have a fairly extensive tradition of defining away UB with
language extentions, -fno-strict-overflow, -fno-strict-aliasing,
-fno-delete-null-pointer-checks etc..
next prev parent reply other threads:[~2020-11-19 8:37 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-16 22:51 [PATCH] tracepoint: Do not fail unregistering a probe due to memory allocation Steven Rostedt
2020-11-16 23:16 ` Steven Rostedt
2020-11-17 19:15 ` Mathieu Desnoyers
2020-11-17 19:21 ` Steven Rostedt
2020-11-17 19:47 ` Mathieu Desnoyers
2020-11-17 20:34 ` Steven Rostedt
2020-11-17 20:58 ` Steven Rostedt
2020-11-17 21:22 ` Mathieu Desnoyers
2020-11-17 22:16 ` Steven Rostedt
2020-11-17 23:08 ` Mathieu Desnoyers
2020-11-18 1:11 ` Steven Rostedt
2020-11-17 21:08 ` Mathieu Desnoyers
2020-11-18 13:21 ` violating function pointer signature Peter Zijlstra
2020-11-18 13:59 ` Florian Weimer
2020-11-18 14:12 ` Peter Zijlstra
2020-11-18 14:18 ` Florian Weimer
2020-11-18 14:34 ` [PATCH v3] tracepoint: Do not fail unregistering a probe due to memory allocation Steven Rostedt
2020-11-24 5:59 ` Matt Mullins
2020-11-18 14:22 ` violating function pointer signature Steven Rostedt
2020-11-18 19:46 ` Alexei Starovoitov
2020-11-18 20:02 ` Steven Rostedt
2020-11-18 14:02 ` Steven Rostedt
2020-11-18 16:01 ` Mathieu Desnoyers
2020-11-18 16:19 ` David Laight
2020-11-18 16:50 ` Nick Desaulniers
2020-11-18 17:17 ` Steven Rostedt
2020-11-18 18:12 ` Segher Boessenkool
2020-11-18 18:31 ` Florian Weimer
2020-11-18 18:55 ` Segher Boessenkool
2020-11-18 18:58 ` Steven Rostedt
2020-11-18 18:59 ` Steven Rostedt
2020-11-18 19:11 ` Segher Boessenkool
2020-11-18 19:33 ` Steven Rostedt
2020-11-18 19:48 ` Segher Boessenkool
2020-11-18 20:44 ` Steven Rostedt
2020-11-19 8:21 ` Peter Zijlstra
2020-11-19 8:36 ` Peter Zijlstra [this message]
2020-11-19 14:37 ` Segher Boessenkool
2020-11-19 14:59 ` Steven Rostedt
2020-11-19 16:35 ` Segher Boessenkool
2020-11-19 17:42 ` David Laight
2020-11-19 19:27 ` Segher Boessenkool
2020-11-19 17:04 ` Alexei Starovoitov
2020-11-19 17:30 ` Steven Rostedt
2020-11-20 1:31 ` Nick Desaulniers
2020-11-17 21:33 ` [PATCH] tracepoint: Do not fail unregistering a probe due to memory allocation Kees Cook
2020-11-17 22:19 ` Steven Rostedt
2020-11-17 23:12 ` Mathieu Desnoyers
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