Date: Thu, 8 Jan 2009 13:03:38 +0100
From: Adam Osuchowski <adwol@zonk.pl>
To: linux-kernel@vger.kernel.org
Subject: Is 386 processor still supported?
Message-ID: <20090108120338.6b8b4567@zonk.pl>
Reply-To: Adam Osuchowski <adwol@zonk.pl>
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Recently, I found such piece of code in kernel 2.6.28 compiled for 386
processor:

# grep M386 .config
CONFIG_M386=y
# objdump -d vmlinux | grep -A11 '<_spin_lock>:'
c0321827 <_spin_lock>:
c0321827:	89 e2                	mov    %esp,%edx
c0321829:	81 e2 00 f0 ff ff    	and    $0xfffff000,%edx
c032182f:	ff 42 14             	incl   0x14(%edx)
c0321832:	ba 00 01 00 00       	mov    $0x100,%edx
c0321837:	f0 66 0f c1 10       	lock xadd %dx,(%eax)
c032183c:	38 f2                	cmp    %dh,%dl
c032183e:	74 06                	je     c0321846 <_spin_lock+0x1f>
c0321840:	f3 90                	pause  
c0321842:	8a 10                	mov    (%eax),%dl
c0321844:	eb f6                	jmp    c032183c <_spin_lock+0x15>
c0321846:	c3                   	ret    

But there is no xadd instruction on 386 processors. It is available on
486+ only. I have no chance to run this kernel on real 386 box, so I can't
check it in practice, but I think it will not run.

It is not compiler problem because it is explicitly written in assembly
in __raw_spin_lock() function (include/asm-x86/spinlock.h) and there is
no alternative code depending on CONFIG_M386.

Regards.
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