linux-kernel - Re: Is 386 processor still supported?

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Message-ID: <20090108132442.GB8015@localhost>
Date:	Thu, 8 Jan 2009 16:24:42 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Adam Osuchowski <adwol@...k.pl>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, Nick Piggin <npiggin@...e.de>
Subject: Re: Is 386 processor still supported?

[Jiri Kosina - Thu, Jan 08, 2009 at 02:05:48PM +0100]
| 
| [ CCs added ]
| 
| On Thu, 8 Jan 2009, Adam Osuchowski wrote:
| 
| > 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.
| 
| Hmm, this really looks like a bug to me. How about something like this 
| (untested).
| 
| 
| From: Jiri Kosina <jkosina@...e.cz>
| Subject: x86: make spinlocks available on machines without xadd insn
| 
| Current kernel wouldn't compile on ancient x86 machines that don't support 
| xadd instruction, as ticket spinlocks implementation unconditionally uses 
| it.
| 
| On machines without CONFIG_X86_XADD, use old-style byte spinlock 
| implementation instead.
| 
| Reported-by: Adam Osuchowski <adwol@...k.pl>
| Signed-off-by: Jiri Kosina <jkosina@...e.cz>
| 
| diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
| index d17c919..b3bc71b 100644
| --- a/arch/x86/include/asm/spinlock.h
| +++ b/arch/x86/include/asm/spinlock.h
| @@ -236,6 +236,40 @@ static inline void __byte_spin_unlock(raw_spinlock_t *lock)
|  	bl->lock = 0;
|  }
|  #else  /* !CONFIG_PARAVIRT */
| +
| +/* old x86 machines do not have xadd insns, use old-style locks for them */
| +#ifndef CONFIG_X86_XADD
| +static inline int __raw_spin_is_locked(raw_spinlock_t *lock)
| +{
| +	return __byte_spin_is_locked(lock);
| +}
| +
| +static inline int __raw_spin_is_contended(raw_spinlock_t *lock)
| +{
| +	return __byte_spin_is_contended(lock);
| +}
| +
| +static __always_inline void __raw_spin_lock(raw_spinlock_t *lock)
| +{
| +	__byte_spin_lock(lock);
| +}
| +
| +static __always_inline int __raw_spin_trylock(raw_spinlock_t *lock)
| +{
| +	return __byte_spin_trylock(lock);
| +}
| +
| +static __always_inline void __raw_spin_unlock(raw_spinlock_t *lock)
| +{
| +	__byte_spin_unlock(lock);
| +}
| +
| +static __always_inline void __raw_spin_lock_flags(raw_spinlock_t *lock,
| +						  unsigned long flags)
| +{
| +	__raw_spin_lock(lock);
| +}
| +#else /* CONFIG_X86_XADD */
|  static inline int __raw_spin_is_locked(raw_spinlock_t *lock)
|  {
|  	return __ticket_spin_is_locked(lock);
| @@ -267,6 +301,7 @@ static __always_inline void __raw_spin_lock_flags(raw_spinlock_t *lock,
|  	__raw_spin_lock(lock);
|  }
|  
| +#endif  /* CONFIG_X86_XADD */
|  #endif	/* CONFIG_PARAVIRT */
|  
|  static inline void __raw_spin_unlock_wait(raw_spinlock_t *lock)
| 

Jiri I could be wrong but it seems __byte_spin_lock is implemented
under CONFIG_PARAVIRT and now referred under #else  /* !CONFIG_PARAVIRT */
At least I didn'y found additional implementaion in tree.
Did I miss anything?

		- Cyrill -
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