From: erik quanstrom <quanstro@quanstro.net>
To: 9fans@9fans.net
Subject: [9fans] ainc() 386/amd64 differences
Date: Wed, 14 May 2014 16:34:48 -0400 [thread overview]
Message-ID: <ffbe73aa19ef921d30a236b5a3919060@ladd.quanstro.net> (raw)
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
next reply other threads:[~2014-05-14 20:34 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-14 20:34 erik quanstrom [this message]
2014-05-14 20:57 ` Charles Forsyth
2014-05-14 21:26 ` erik quanstrom
2014-05-14 21:46 ` erik quanstrom
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