linux-kernel - Re: violating function pointer signature

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Message-ID: <20201119095951.30269233@gandalf.local.home>
Date:   Thu, 19 Nov 2020 09:59:51 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Florian Weimer <fw@...eb.enyo.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Matt Mullins <mmullins@...x.us>,
        Ingo Molnar <mingo@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-toolchains@...r.kernel.org
Subject: Re: violating function pointer signature

On Thu, 19 Nov 2020 08:37:35 -0600
Segher Boessenkool <segher@...nel.crashing.org> wrote:

> > Note that we have a fairly extensive tradition of defining away UB with
> > language extentions, -fno-strict-overflow, -fno-strict-aliasing,  
> 
> These are options to make a large swath of not correct C programs
> compile (and often work) anyway.  This is useful because there are so
> many such programs, because a) people did not lint; and/or b) the
> problem never was obvious with some other (or older) compiler; and/or
> c) people do not care about writing portable C and prefer writing in
> their own non-C dialect.


Note, this is not about your average C program. This is about the Linux
kernel, which already does a lot of tricks in C. There's a lot of code in
assembly that gets called from C (and vise versa). We modify code on the
fly (which tracepoints use two methods of that - with asm-goto/jump-labels
and static functions).

As for your point c), I'm not sure what you mean about portable C (stuck to
a single compiler, or stuck to a single architecture?). Linux obviously
supports multiple architectures (more than any other OS), but it is pretty
stuck to gcc as a compiler (with LLVM just starting to work too).

We are fine with being stuck to a compiler if it gives us what we want.

-- Steve