linux-kernel - Re: [PATCH] objtool: Detect assembly code falling through to INT3 padding

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Message-ID: <84F157C1-AD98-473D-9CF6-2A26A499DECF@zytor.com>
Date:   Sat, 19 May 2018 01:18:59 -0700
From:   hpa@...or.com
To:     Alexey Dobriyan <adobriyan@...il.com>,
        Ingo Molnar <mingo@...nel.org>
CC:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Anvin <h.peter.anvin@...el.com>,
        kernel test robot <xiaolong.ye@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        tipbuild@...or.com, LKP <lkp@...org>
Subject: Re: [PATCH] objtool: Detect assembly code falling through to INT3 padding

On May 18, 2018 10:51:36 AM PDT, Alexey Dobriyan <adobriyan@...il.com> wrote:
>On Fri, May 18, 2018 at 09:18:14AM +0200, Ingo Molnar wrote:
>> The concept of built-in kernel tooling working at the machine code
>level is just 
>> so powerful - we should have added our own KCC compiler 20 years ago.
>
>...for two very serious reasons
>
>* C as a language moves very slowly, last help from the comittee were
>  C99 intializers which are OK, but, say, memory model was explictly
>  rejected. However the project expands and becomes more complex much
>  faster than C working group sets up meetings. Compiler authors help
>with extensions but ultimately can not be relied on (see "inline"
>saga).
>
>  Recently everyone was celebrating new and improved min() and max()
> macros admiring creativity and knowledge of intricate language details
>  (me too, don't get this wrong).
>
>  Now this is how it can be done in a language which is not stupid:
>
>	constexpr int min(int a, int b)
>	{
>		return a < b ? a : b;
>	}
>
>  That's literally all. And you can also do
>
>	template<typename T>
>	void min(T a, char b) = delete;
>
>	template<typename T>
>	void min(char a, T b) = delete;
>
>  because "char" is char.
>
>  Having control over compiler things like that can be addded more
>  quickly.
>
>
>* insulating the project from the whims of compiler authors who every
>  once in a while use "undefined behaviour" or other kinds of language
>  lawyering to do strange things.
>
>  Other serious projects do this too. Database people use O_DIRECT
>  to insulate themselves from kernel people for the very same reasons.

Sounds like you are proposing switching to C++ more than anything else.

*Steps aside and grabs popcorn*
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.