linux-kernel - Re: Does anyone care about gcc 3.x support for x86 anymore?

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Message-ID: <20100520124453.GC2734@elte.hu>
Date:	Thu, 20 May 2010 14:44:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Eric Dumazet <eric.dumazet@...il.com>, mingo@...hat.com,
	linux-kernel@...r.kernel.org, suresh.b.siddha@...el.com,
	tglx@...utronix.de, avi@...hat.com,
	linux-tip-commits@...r.kernel.org
Subject: Re: Does anyone care about gcc 3.x support for x86 anymore?


* H. Peter Anvin <hpa@...or.com> wrote:

> On 05/19/2010 04:10 PM, Mauro Carvalho Chehab wrote:
> > 
> > However, if the problems are just performance/dead 
> > code removal, I would just add a big warning if 
> > someone tries to compile x86 with it. I don't like 
> > very much the idea of having different minimum gcc 
> > requirements for each architecture, except if gcc is 
> > producing a broken code.
> > 
> 
> I should clarify the problem.  The problems we have seen 
> are related to constant propagation, which causes gcc3 
> to die when there is an assembly constraint like:
> 
> 	asm("..." : : "i" (foo));
> 
> ... since "foo" isn't constant as far as it is 
> concerned.  We can put in workarounds, but it's real 
> effort to keep it alive that probably isn't well spent.
> 
> Similarly, lack of constant propagation can cause code 
> that should have been compile-time removed to still be 
> there, causing link failures.

Put in a deprecation warning first perhaps?

	Ingo
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