#define	argp		16
#define	entry	0
#define	entrycode	168
#define	exit		4
#define	exitcode	40
#define	func		8
#define	orig1	24
#define	orig2	28
#define	probe1	32
#define	probe2	36
#define	rval		20
#define	saveret	12

#define	ax	0
#define	cx	1
#define	dx	2
#define	bx	3
#define	bp	4
#define	si	5
#define	di	6
#define	sp	7

#define call0		BYTE $0xe8; BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00
#define pop(reg)	BYTE $(0x58 + (reg))
#define popa		BYTE $0x61
#define popf		BYTE $0x9d
#define push(reg)	BYTE $(0x50 + (reg))
#define pusha		BYTE $0x60
#define pushf		BYTE $0x9c

TEXT pentrytmpl(SB), 1, $0
			/* 11(sp) first arg to func */
			/* 10(sp) call func somewhere */
			/* 9(sp) synthetized call at func start */
	pushf	/* 8(sp)			*/
	pusha	/* 0(sp) ⋯ 7(sp)	*/ 
	call0
	pop(ax)

	/* pushf + pusha + call0 = 7 bytes */
	SUBL $(7 + entrycode), AX

	/* save argp */
	LEAL 44(SP), BX
	MOVL BX, argp(AX)

	/* save return address of probed function */
	MOVL 40(SP), BX
	MOVL BX, saveret(AX)

	/* trap function return to probe exit */
	LEAL	exitcode(AX), BX
	MOVL BX, 40(SP)

	/* uninstall probe  */
	MOVL func(AX), BX
	MOVL orig1(AX), CX
	MOVL orig2(AX), DX
	MOVL CX, 0(BX)
	MOVL DX, 4(BX)

	/* patch up return address so we return to start of function */
	MOVL BX, 36(SP)

	/* call the hook last */
	PUSHL AX
	CALL entry(AX)
	POPL AX

	popa
	popf
	RET
	END

TEXT pexittmpl(SB), 1, $0
	push(ax)	/* 9(sp)			*/
	pushf	/* 8(sp)			*/
	pusha	/* 0(sp) ⋯ 7(sp)	*/ 
	call0
	pop(ax)

	/* pushf + pushf + pusha + call0 = 8 bytes */
	SUBL $(8 + exitcode), AX

	/* save return value */
	MOVL 36(SP), BX
	MOVL BX, rval(AX)

	/* call the hook first */
	PUSHL AX
	PUSHL AX
	CALL exit(AX)
	POPL AX
	POPL AX

	/* reinstall probe */
	MOVL func(AX), BX
	MOVL probe1(AX), CX
	MOVL probe2(AX), DX
	MOVL CX, 0(BX)
	MOVL DX, 4(BX)

	MOVL saveret(AX), BX
	MOVL BX, 36(SP)

	popa
	popf
	RET
	END