linux-kernel - Re: Definition of BUG on x86

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Message-ID: <20090219121027.GB1703@elte.hu>
Date:	Thu, 19 Feb 2009 13:10:27 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Petr Tesarik <ptesarik@...e.cz>, "H. Peter Anvin" <hpa@...or.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Definition of BUG on x86


* Petr Tesarik <ptesarik@...e.cz> wrote:

> So, the only method I could invent was using gas macros. It 
> works but is quite ugly, because it relies on the actual 
> assembler instruction which is generated by the compiler. Now, 
> AFAIK gcc has always translated "for(;;)" into a jump to self, 
> and that with any conceivable compiler options, but I don't 
> know anything about Intel cc.

> +static inline __noreturn void discarded_jmp(void)
> +{
> +	asm volatile(".macro jmp target\n"
> +		     "\t.purgem jmp\n"
> +		     ".endm\n");
> +	for (;;) ;
> +}

hm, that's very fragile.

Why not just:

 static inline __noreturn void x86_u2d(void)
 {
	asm volatile("u2d\n");
 }

If GCC emits a bogus warning about _that_, then it's a bug in 
the compiler that should be fixed.

	Ingo
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