Date: Tue, 03 Dec 1996 00:54:40 -0600 From: Chris Csanady <ccsanady@friley216.res.iastate.edu> To: freebsd-smp@freebsd.org Subject: spin locks... Message-ID: <199612030654.AAA12221@friley216.res.iastate.edu>
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Its something we could use, so I thought I'd give it a shot. I thought it
would make a nice first assembly project, right? Yeah.. sure. I have never
been so frustrated with something so obviously simple.
When I try to link it into a test program, it segfaults. The only way I
could obtain predictable behavior was to take out the cmpxchg and lock.
Could someone please point out my error here?
.text
.align 2,0x90
.globl _get_spinlock
_get_spinlock:
pushl %eax
pushl %ecx
pushl %edx
movl _smp_active, %eax
cmpl $0, %eax
jne 1f
jmp 4
1: movl 4(%esp), %edx
movl $1, %ecx
2: lock
cmpxchg %ecx, (%edx)
je 3f
jmp 4
3: cmpl %ecx, (%edx)
je 3b
jmp 2b
4: popl %edx
popl %ecx
popl %eax
ret
--Chris Csanady
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