Messages in this thread | | | Date | Thu, 8 Jan 2009 16:24:42 +0300 | From | Cyrill Gorcunov <> | Subject | Re: Is 386 processor still supported? |
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[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@suse.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@zonk.pl> | Signed-off-by: Jiri Kosina <jkosina@suse.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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