linux-kernel - Re: Linux doesn't follow x86/x86-64 ABI wrt direction flag

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Date:	Wed, 5 Mar 2008 12:42:34 -0800
From:	Joe Buck <Joe.Buck@...opsys.COM>
To:	Michael Matz <matz@...e.de>
Cc:	Aurelien Jarno <aurelien@...el32.net>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	gcc@....gnu.org
Subject: Re: Linux doesn't follow x86/x86-64 ABI wrt direction flag

On Wed, Mar 05, 2008 at 09:38:13PM +0100, Michael Matz wrote:
> Hi,
> 
> On Wed, 5 Mar 2008, Aurelien Jarno wrote:
> 
> > > So I think gcc at least needs an *option* to revert to the old behavior,
> > > and there's a good argument to make it the default for now, at least for
> > > x86/x86-64 on Linux.
> > 
> > And for other kernels. I tested OpenBSD 4.1, FreeBSD 6.3, NetBSD 4.0, 
> > they have the same behaviour as Linux, that is they don't clear DF 
> > before calling the signal handler.
> 
> Sigh.  We could perhaps insert a cld for all functions which can be 
> recognized as possible signal handlers and call other unknown or string 
> functions.  But it's probably even faster to emit cld in front of the 
> inline copies of mem functions again :-(

Yes, if there are four kernels that get it "wrong", that effectively means
that the ABI document doesn't describe reality and gcc has to adjust.
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