linux-kernel - Re: [PATCH] x86, vsyscall: Fix build warning in vsyscall

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Message-ID: <BANLkTi=W1xFdoSFxnNBGX9gt_pYOH4oF=A@mail.gmail.com>
Date:	Tue, 14 Jun 2011 14:24:02 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andy Lutomirski <luto@....edu>,
	Rakib Mullick <rakib.mullick@...il.com>, hpa@...or.com,
	tglx@...utronix.de, x86@...nel.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86, vsyscall: Fix build warning in vsyscall_64.c

On Tue, Jun 14, 2011 at 2:16 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> I think correctness trumps code size and turning BUG() and BUG_ON()
> into a NOP is just crazy ...

Umm. It's even CRAZIER to turn it into a "compiler generates random code".

Which is what "unreachable()" ends up doing (different compilers will
generate different things - ranging from an infinite loop, to a "nop
with random behavior after it because gcc decided that it doesn't need
to pop arguments off the stack and just runs into random code
instead").

So a NOP is a *hell* of a lot better than turning BUG_ON() into
something random.

The only (and I mean *only*) valid use-case for unreachable() is after
an inline asm that really causes the next instruction to be
unreachable(), but the compiler just doesn't understand it. It is
*not* valid for that kind of crazy "if (condition) do-random-thing"
crap.

Seriously. If you want a "do random thing" thing, don't call it
BUG_ON(). Call it "I_M_A_FUCKING_MORON()".

There is no way I will ever accept a moronic patch like that.

Really.

                     Linus
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