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From: Ingo Molnar <mingo@kernel.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Denys Vlasenko <dvlasenk@redhat.com>
Subject: Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings
Date: Thu, 2 Mar 2017 15:46:39 +0100	[thread overview]
Message-ID: <20170302144639.GA8969@gmail.com> (raw)
In-Reply-To: <20170302140830.6cryk3uepqnrrqef@treble>


* Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> > > > Well, technically an invalid opcode is shorter code than generating an 
> > > > (integer) division by zero exception, right?
> > > 
> > > What does that matter if it's the wrong behavior?
> > 
> > Well, both terminate the program, and it's obvious if you look at it with a 
> > debugger what happened, right?
> 
> If it were obvious, we wouldn't be having this discussion :-)

Touche ;-)

> The only thing obvious to me was that gcc mysteriously removed a bunch of code 
> and replaced it with a 'ud2' instruction in the middle of the function for no 
> apparent reason.

I don't know what their motivation was, but if it's not a bug, if it was done 
intentionally, then I'd guess it's roughly the argument I made: in simple 
testcases it can be argued to be a code size improvement, plus it's probably 
allowed by the letter of the compiler standards (program termination behavior is 
notoriously platform dependent and thus vaguely specified) - but for real-life 
code I very much agree that it's a step backward in generated code quality...

Thanks,

	Ingo

  reply	other threads:[~2017-03-02 14:49 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-10 12:56 [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann
2016-10-10 20:23 ` Josh Poimboeuf
2016-10-11  8:08   ` Arnd Bergmann
2016-10-11 12:20     ` Josh Poimboeuf
2016-10-11 13:30       ` Arnd Bergmann
2016-10-11 15:05         ` Josh Poimboeuf
2016-10-11 15:51           ` Josh Poimboeuf
2016-10-11 20:38             ` Arnd Bergmann
2016-10-12 13:01               ` Josh Poimboeuf
2016-10-13 12:46               ` Another gcc corruption bug (was Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings) Josh Poimboeuf
2016-10-13 17:57                 ` Denys Vlasenko
2016-10-13 20:15                   ` Josh Poimboeuf
2017-03-01  9:34               ` [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann
2017-03-01  9:45                 ` Arnd Bergmann
2017-03-01 14:40                   ` Josh Poimboeuf
2017-03-01 15:27                     ` Arnd Bergmann
2017-03-01 16:53                       ` Josh Poimboeuf
2017-03-01 22:05                         ` Arnd Bergmann
2017-03-01 22:42                         ` Arnd Bergmann
2017-03-02  1:03                           ` Josh Poimboeuf
2017-03-02  6:31                             ` Ingo Molnar
2017-03-02 12:49                               ` Josh Poimboeuf
2017-03-02 13:46                                 ` Ingo Molnar
2017-03-02 14:08                                   ` Josh Poimboeuf
2017-03-02 14:46                                     ` Ingo Molnar [this message]
2017-03-02 22:49                             ` Arnd Bergmann
2017-03-02 23:05                               ` Josh Poimboeuf
2017-03-03  8:58                                 ` Arnd Bergmann
2017-03-03 11:27                                   ` Arnd Bergmann
2017-03-01 14:31                 ` Josh Poimboeuf
2017-03-01 15:21                   ` Arnd Bergmann
2017-03-02 18:25                     ` Josh Poimboeuf
2017-03-02 22:43                       ` Arnd Bergmann
2017-03-02 22:57                         ` [PATCH] objtool: fix another gcc jump table detection issue Josh Poimboeuf
2017-03-02 23:01                           ` Arnd Bergmann
2016-10-11  1:53 ` [PATCH] objtool: support '-mtune=atom' stack frame setup instruction Josh Poimboeuf

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