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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Tue, 14 Jun 2011 14:24:02 -0700
Message-ID: <BANLkTi=W1xFdoSFxnNBGX9gt_pYOH4oF=A@mail.gmail.com>
Subject: Re: [PATCH] x86, vsyscall: Fix build warning in vsyscall_64.c
To: Ingo Molnar <mingo@elte.hu>
Cc: Andy Lutomirski <luto@mit.edu>, Rakib Mullick <rakib.mullick@gmail.com>,
        hpa@zytor.com, tglx@linutronix.de, x86@kernel.org,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
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On Tue, Jun 14, 2011 at 2:16 PM, Ingo Molnar <mingo@elte.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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