Go Assembly by Example: Sync Atomic

This example is taken from the sync/atomic package which provides low-level atomic memory primitives. The swap operation, implemented by the SwapT functions, is the atomic equivalent of `old = addr addr = new return old`
	package atomic
	import ( "unsafe" )
SwapInt32 atomically stores new into addr and returns the previous addr value.	func SwapInt32(addr *int32, new int32) (old int32)

	#include "textflag.h"
	TEXT ·SwapInt32(SB),NOSPLIT,$0-20 JMP ·SwapUint32(SB)
	TEXT ·SwapUint32(SB),NOSPLIT,$0-20 MOVQ addr+0(FP), BP MOVL new+8(FP), AX
The `XCHGL` instruction is not vulnerable to a Write-After-Read as the bus is locked for the duration of the exchange.	XCHGL AX, 0(BP) MOVL AX, old+16(FP) RET

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