for 386, libc has this definition for ainc
TEXT ainc(SB), $0 /* int ainc(int *); */
MOVL addr+0(FP), BX
ainclp:
MOVL (BX), AX
MOVL AX, CX
INCL CX
LOCK
BYTE $0x0F; BYTE $0xB1; BYTE $0x0B /* CMPXCHGL CX, (BX) */
JNZ ainclp
MOVL CX, AX
RET
the amd64 kernel has had this definition (the pc kernel doesn't define ainc)
TEXT ainc(SB), 1, $-4
MOVL $1, AX
LOCK; XADDL AX, (RARG)
ADDL $1, AX /* overflow if -ve or 0 */
JGT _return
_trap:
XORQ BX, BX
MOVQ (BX), BX /* over under sideways down */
_return:
RET
these are substantially different in two ways.
- the first is not wait free. the second may be wait free.
- the second is geared toward reference counting, and will
trap instead of wrapping. it can't be used for generating
a unique sequence.
i'd like to see the amd64 kernel version replace incref, and
this version of ainc
TEXT ainc(SB), 1, $-4
TEXT ainc32(SB), 1, $-4
MOVL $1, AX
LOCK; XADDL AX, (RARG)
INCL AX
RET
what does the list think?
- erik
