linux-kernel - Re: [BUG] x86: 2.6.27-rc1 does not build with gcc-3.2.3 any more

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Message-ID: <20080730111003.GA23933@elte.hu>
Date:	Wed, 30 Jul 2008 13:10:03 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mikael Pettersson <mikpe@...uu.se>
Cc:	hpa@...or.com, mingo@...hat.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] x86: 2.6.27-rc1 does not build with gcc-3.2.3 any more


* Mikael Pettersson <mikpe@...uu.se> wrote:

> static inline __attribute__((always_inline))
> unsigned char readb(const volatile void *addr)
> {
> 	unsigned char ret;
> 	asm volatile("mov" "b" " %1,%0"
> 		     : "=" "q" (ret)
> 		     : "m" (*(volatile unsigned char *)addr)
> 		     : "memory");
> 	return ret;
> }
> 
> The problem is that "=q" has been broken up into two adjacent
> string literals, and apparently gcc-3.2.3 hasn't done string
> literal concatenation at the time it processes the asm().
> Hence the syntax error. (This is clearly a gcc bug.)
> 
> Switching to gcc-3.3.6 or newer fixes the problem.
> 
> The question is, should the kernel be fixed to compile with 3.2.3
> again (by generating "=q" not "=" "q"), or should the minimum supported
> gcc version be bumped to 3.3.6?
> 
> I have no strong feeling about this, except that I want to use the
> oldest (== least bloated) gcc possible on my 486 test box.

yeah, please send a fix. We could move the '=' from build_mmio_read into 
the argument (explicitly).

	Ingo
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