src/runtime/sys_darwin_386.s - go.git - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // System calls and other sys.stuff for 386, Darwin
 // See http://fxr.watson.org/fxr/source/bsd/kern/syscalls.c?v=xnu-1228
 // or /usr/include/sys/syscall.h (on a Mac) for system call numbers.

 #include "go_asm.h"
 #include "go_tls.h"
 #include "textflag.h"

 // Exit the entire program (like C exit)
 TEXT runtime·exit(SB),NOSPLIT,$0
 	MOVL	$1, AX
 	INT	$0x80
 	MOVL	$0xf1, 0xf1  // crash
 	RET

 // Exit this OS thread (like pthread_exit, which eventually
 // calls __bsdthread_terminate).
 TEXT runtime·exit1(SB),NOSPLIT,$0
 	MOVL	$361, AX
 	INT	$0x80
 	JAE 2(PC)
 	MOVL	$0xf1, 0xf1  // crash
 	RET

 TEXT runtime·open(SB),NOSPLIT,$0
 	MOVL	$5, AX
 	INT	$0x80
 	JAE	2(PC)
 	MOVL	$-1, AX
 	MOVL	AX, ret+12(FP)
 	RET

 TEXT runtime·closefd(SB),NOSPLIT,$0
 	MOVL	$6, AX
 	INT	$0x80
 	JAE	2(PC)
 	MOVL	$-1, AX
 	MOVL	AX, ret+4(FP)
 	RET

 TEXT runtime·read(SB),NOSPLIT,$0
 	MOVL	$3, AX
 	INT	$0x80
 	JAE	2(PC)
 	MOVL	$-1, AX
 	MOVL	AX, ret+12(FP)
 	RET

 TEXT runtime·write(SB),NOSPLIT,$0
 	MOVL	$4, AX
 	INT	$0x80
 	JAE	2(PC)
 	MOVL	$-1, AX
 	MOVL	AX, ret+12(FP)
 	RET

 TEXT runtime·raise(SB),NOSPLIT,$0
 	// Ideally we'd send the signal to the current thread,
 	// not the whole process, but that's too hard on OS X.
 	JMP	runtime·raiseproc(SB)

 TEXT runtime·raiseproc(SB),NOSPLIT,$16
 	MOVL	$20, AX // getpid
 	INT	$0x80
 	MOVL	AX, 4(SP)	// pid
 	MOVL	sig+0(FP), AX
 	MOVL	AX, 8(SP)	// signal
 	MOVL	$1, 12(SP)	// posix
 	MOVL	$37, AX // kill
 	INT	$0x80
 	RET

 TEXT runtime·mmap(SB),NOSPLIT,$0
 	MOVL	$197, AX
 	INT	$0x80
 	MOVL	AX, ret+24(FP)
 	RET

 TEXT runtime·madvise(SB),NOSPLIT,$0
 	MOVL	$75, AX
 	INT	$0x80
 	// ignore failure - maybe pages are locked
 	RET

 TEXT runtime·munmap(SB),NOSPLIT,$0
 	MOVL	$73, AX
 	INT	$0x80
 	JAE	2(PC)
 	MOVL	$0xf1, 0xf1  // crash
 	RET

 TEXT runtime·setitimer(SB),NOSPLIT,$0
 	MOVL	$83, AX
 	INT	$0x80
 	RET

 // OS X comm page time offsets
 // http://www.opensource.apple.com/source/xnu/xnu-1699.26.8/osfmk/i386/cpu_capabilities.h
 #define	cpu_capabilities	0x20
 #define	nt_tsc_base	0x50
 #define	nt_scale	0x58
 #define	nt_shift	0x5c
 #define	nt_ns_base	0x60
 #define	nt_generation	0x68
 #define	gtod_generation	0x6c
 #define	gtod_ns_base	0x70
 #define	gtod_sec_base	0x78

 // called from assembly
 // 64-bit unix nanoseconds returned in DX:AX.
 // I'd much rather write this in C but we need
 // assembly for the 96-bit multiply and RDTSC.
 TEXT runtime·now(SB),NOSPLIT,$40
 	MOVL	$0xffff0000, BP /* comm page base */

 	// Test for slow CPU. If so, the math is completely
 	// different, and unimplemented here, so use the
 	// system call.
 	MOVL	cpu_capabilities(BP), AX
 	TESTL	$0x4000, AX
 	JNZ	systime

 	// Loop trying to take a consistent snapshot
 	// of the time parameters.
 timeloop:
 	MOVL	gtod_generation(BP), BX
 	TESTL	BX, BX
 	JZ	systime
 	MOVL	nt_generation(BP), CX
 	TESTL	CX, CX
 	JZ	timeloop
 	RDTSC
 	MOVL	nt_tsc_base(BP), SI
 	MOVL	(nt_tsc_base+4)(BP), DI
 	MOVL	SI, 0(SP)
 	MOVL	DI, 4(SP)
 	MOVL	nt_scale(BP), SI
 	MOVL	SI, 8(SP)
 	MOVL	nt_ns_base(BP), SI
 	MOVL	(nt_ns_base+4)(BP), DI
 	MOVL	SI, 12(SP)
 	MOVL	DI, 16(SP)
 	CMPL	nt_generation(BP), CX
 	JNE	timeloop
 	MOVL	gtod_ns_base(BP), SI
 	MOVL	(gtod_ns_base+4)(BP), DI
 	MOVL	SI, 20(SP)
 	MOVL	DI, 24(SP)
 	MOVL	gtod_sec_base(BP), SI
 	MOVL	(gtod_sec_base+4)(BP), DI
 	MOVL	SI, 28(SP)
 	MOVL	DI, 32(SP)
 	CMPL	gtod_generation(BP), BX
 	JNE	timeloop

 	// Gathered all the data we need. Compute time.
 	//	((tsc - nt_tsc_base) * nt_scale) >> 32 + nt_ns_base - gtod_ns_base + gtod_sec_base*1e9
 	// The multiply and shift extracts the top 64 bits of the 96-bit product.
 	SUBL	0(SP), AX // DX:AX = (tsc - nt_tsc_base)
 	SBBL	4(SP), DX

 	// We have x = tsc - nt_tsc_base - DX:AX to be
 	// multiplied by y = nt_scale = 8(SP), keeping the top 64 bits of the 96-bit product.
 	// x*y = (x&0xffffffff)*y + (x&0xffffffff00000000)*y
 	// (x*y)>>32 = ((x&0xffffffff)*y)>>32 + (x>>32)*y
 	MOVL	DX, CX // SI = (x&0xffffffff)*y >> 32
 	MOVL	$0, DX
 	MULL	8(SP)
 	MOVL	DX, SI

 	MOVL	CX, AX // DX:AX = (x>>32)*y
 	MOVL	$0, DX
 	MULL	8(SP)

 	ADDL	SI, AX	// DX:AX += (x&0xffffffff)*y >> 32
 	ADCL	$0, DX

 	// DX:AX is now ((tsc - nt_tsc_base) * nt_scale) >> 32.
 	ADDL	12(SP), AX	// DX:AX += nt_ns_base
 	ADCL	16(SP), DX
 	SUBL	20(SP), AX	// DX:AX -= gtod_ns_base
 	SBBL	24(SP), DX
 	MOVL	AX, SI	// DI:SI = DX:AX
 	MOVL	DX, DI
 	MOVL	28(SP), AX	// DX:AX = gtod_sec_base*1e9
 	MOVL	32(SP), DX
 	MOVL	$1000000000, CX
 	MULL	CX
 	ADDL	SI, AX	// DX:AX += DI:SI
 	ADCL	DI, DX
 	RET

 systime:
 	// Fall back to system call (usually first call in this thread)
 	LEAL	16(SP), AX	// must be non-nil, unused
 	MOVL	AX, 4(SP)
 	MOVL	$0, 8(SP)	// time zone pointer
 	MOVL	$0, 12(SP)	// required as of Sierra; Issue 16570
 	MOVL	$116, AX // SYS_GETTIMEOFDAY
 	INT	$0x80
 	CMPL	AX, $0
 	JNE	inreg
 	MOVL	16(SP), AX
 	MOVL	20(SP), DX
 inreg:
 	// sec is in AX, usec in DX
 	// convert to DX:AX nsec
 	MOVL	DX, BX
 	MOVL	$1000000000, CX
 	MULL	CX
 	IMULL	$1000, BX
 	ADDL	BX, AX
 	ADCL	$0, DX
 	RET

 // func now() (sec int64, nsec int32)
 TEXT time·now(SB),NOSPLIT,$0
 	CALL	runtime·now(SB)
 	MOVL	$1000000000, CX
 	DIVL	CX
 	MOVL	AX, sec+0(FP)
 	MOVL	$0, sec+4(FP)
 	MOVL	DX, nsec+8(FP)
 	RET

 // func nanotime() int64
 TEXT runtime·nanotime(SB),NOSPLIT,$0
 	CALL	runtime·now(SB)
 	MOVL	AX, ret_lo+0(FP)
 	MOVL	DX, ret_hi+4(FP)
 	RET

 TEXT runtime·sigprocmask(SB),NOSPLIT,$0
 	MOVL	$329, AX  // pthread_sigmask (on OS X, sigprocmask==entire process)
 	INT	$0x80
 	JAE	2(PC)
 	MOVL	$0xf1, 0xf1  // crash
 	RET

 TEXT runtime·sigaction(SB),NOSPLIT,$0
 	MOVL	$46, AX
 	INT	$0x80
 	JAE	2(PC)
 	MOVL	$0xf1, 0xf1  // crash
 	RET

 TEXT runtime·sigfwd(SB),NOSPLIT,$0-16
 	MOVL	fn+0(FP), AX
 	MOVL	sig+4(FP), BX
 	MOVL	info+8(FP), CX
 	MOVL	ctx+12(FP), DX
 	MOVL	SP, SI
 	SUBL	$32, SP
 	ANDL	$~15, SP	// align stack: handler might be a C function
 	MOVL	BX, 0(SP)
 	MOVL	CX, 4(SP)
 	MOVL	DX, 8(SP)
 	MOVL	SI, 12(SP)	// save SI: handler might be a Go function
 	CALL	AX
 	MOVL	12(SP), AX
 	MOVL	AX, SP
 	RET

 // Sigtramp's job is to call the actual signal handler.
 // It is called with the following arguments on the stack:
 //	0(SP)	"return address" - ignored
 //	4(SP)	actual handler
 //	8(SP)	siginfo style
 //	12(SP)	signal number
 //	16(SP)	siginfo
 //	20(SP)	context
 TEXT runtime·sigtramp(SB),NOSPLIT,$20
 	MOVL	sig+8(FP), BX
 	MOVL	BX, 0(SP)
 	MOVL	info+12(FP), BX
 	MOVL	BX, 4(SP)
 	MOVL	ctx+16(FP), BX
 	MOVL	BX, 8(SP)
 	CALL	runtime·sigtrampgo(SB)

 	// call sigreturn
 	MOVL	ctx+16(FP), CX
 	MOVL	infostyle+4(FP), BX
 	MOVL	$0, 0(SP)	// "caller PC" - ignored
 	MOVL	CX, 4(SP)
 	MOVL	BX, 8(SP)
 	MOVL	$184, AX	// sigreturn(ucontext, infostyle)
 	INT	$0x80
 	MOVL	$0xf1, 0xf1  // crash
 	RET

 TEXT runtime·sigaltstack(SB),NOSPLIT,$0
 	MOVL	$53, AX
 	INT	$0x80
 	JAE	2(PC)
 	MOVL	$0xf1, 0xf1  // crash
 	RET

 TEXT runtime·usleep(SB),NOSPLIT,$32
 	MOVL	$0, DX
 	MOVL	usec+0(FP), AX
 	MOVL	$1000000, CX
 	DIVL	CX
 	MOVL	AX, 24(SP)  // sec
 	MOVL	DX, 28(SP)  // usec

 	// select(0, 0, 0, 0, &tv)
 	MOVL	$0, 0(SP)  // "return PC" - ignored
 	MOVL	$0, 4(SP)
 	MOVL	$0, 8(SP)
 	MOVL	$0, 12(SP)
 	MOVL	$0, 16(SP)
 	LEAL	24(SP), AX
 	MOVL	AX, 20(SP)
 	MOVL	$93, AX
 	INT	$0x80
 	RET

 // func bsdthread_create(stk, arg unsafe.Pointer, fn uintptr) int32
 // System call args are: func arg stack pthread flags.
 TEXT runtime·bsdthread_create(SB),NOSPLIT,$32
 	MOVL	$360, AX
 	// 0(SP) is where the caller PC would be; kernel skips it
 	MOVL	fn+8(FP), BX
 	MOVL	BX, 4(SP)	// func
 	MOVL	arg+4(FP), BX
 	MOVL	BX, 8(SP)	// arg
 	MOVL	stk+0(FP), BX
 	MOVL	BX, 12(SP)	// stack
 	MOVL    $0, 16(SP)      // pthread
 	MOVL	$0x1000000, 20(SP)	// flags = PTHREAD_START_CUSTOM
 	INT	$0x80
 	JAE	4(PC)
 	NEGL	AX
 	MOVL	AX, ret+12(FP)
 	RET
 	MOVL	$0, AX
 	MOVL	AX, ret+12(FP)
 	RET

 // The thread that bsdthread_create creates starts executing here,
 // because we registered this function using bsdthread_register
 // at startup.
 //	AX = "pthread" (= 0x0)
 //	BX = mach thread port
 //	CX = "func" (= fn)
 //	DX = "arg" (= m)
 //	DI = stack top
 //	SI = flags (= 0x1000000)
 //	SP = stack - C_32_STK_ALIGN
 TEXT runtime·bsdthread_start(SB),NOSPLIT,$0
 	// set up ldt 7+id to point at m->tls.
 	LEAL	m_tls(DX), BP
 	MOVL	m_id(DX), DI
 	ADDL	$7, DI	// m0 is LDT#7. count up.
 	// setldt(tls#, &tls, sizeof tls)
 	PUSHAL	// save registers
 	PUSHL	$32	// sizeof tls
 	PUSHL	BP	// &tls
 	PUSHL	DI	// tls #
 	CALL	runtime·setldt(SB)
 	POPL	AX
 	POPL	AX
 	POPL	AX
 	POPAL

 	// Now segment is established. Initialize m, g.
 	get_tls(BP)
 	MOVL    m_g0(DX), AX
 	MOVL	AX, g(BP)
 	MOVL	DX, g_m(AX)
 	MOVL	BX, m_procid(DX)	// m->procid = thread port (for debuggers)
 	CALL	runtime·stackcheck(SB)		// smashes AX
 	CALL	CX	// fn()
 	CALL	runtime·exit1(SB)
 	RET

 // func bsdthread_register() int32
 // registers callbacks for threadstart (see bsdthread_create above
 // and wqthread and pthsize (not used).  returns 0 on success.
 TEXT runtime·bsdthread_register(SB),NOSPLIT,$40
 	MOVL	$366, AX
 	// 0(SP) is where kernel expects caller PC; ignored
 	MOVL	$runtime·bsdthread_start(SB), 4(SP)	// threadstart
 	MOVL	$0, 8(SP)	// wqthread, not used by us
 	MOVL	$0, 12(SP)	// pthsize, not used by us
 	MOVL	$0, 16(SP)	// dummy_value [sic]
 	MOVL	$0, 20(SP)	// targetconc_ptr
 	MOVL	$0, 24(SP)	// dispatchqueue_offset
 	INT	$0x80
 	JAE	4(PC)
 	NEGL	AX
 	MOVL	AX, ret+0(FP)
 	RET
 	MOVL	$0, AX
 	MOVL	AX, ret+0(FP)
 	RET

 // Invoke Mach system call.
 // Assumes system call number in AX,
 // caller PC on stack, caller's caller PC next,
 // and then the system call arguments.
 //
 // Can be used for BSD too, but we don't,
 // because if you use this interface the BSD
 // system call numbers need an extra field
 // in the high 16 bits that seems to be the
 // argument count in bytes but is not always.
 // INT $0x80 works fine for those.
 TEXT runtime·sysenter(SB),NOSPLIT,$0
 	POPL	DX
 	MOVL	SP, CX
 	BYTE $0x0F; BYTE $0x34;  // SYSENTER
 	// returns to DX with SP set to CX

 TEXT runtime·mach_msg_trap(SB),NOSPLIT,$0
 	MOVL	$-31, AX
 	CALL	runtime·sysenter(SB)
 	MOVL	AX, ret+28(FP)
 	RET

 TEXT runtime·mach_reply_port(SB),NOSPLIT,$0
 	MOVL	$-26, AX
 	CALL	runtime·sysenter(SB)
 	MOVL	AX, ret+0(FP)
 	RET

 TEXT runtime·mach_task_self(SB),NOSPLIT,$0
 	MOVL	$-28, AX
 	CALL	runtime·sysenter(SB)
 	MOVL	AX, ret+0(FP)
 	RET

 // Mach provides trap versions of the semaphore ops,
 // instead of requiring the use of RPC.

 // func mach_semaphore_wait(sema uint32) int32
 TEXT runtime·mach_semaphore_wait(SB),NOSPLIT,$0
 	MOVL	$-36, AX
 	CALL	runtime·sysenter(SB)
 	MOVL	AX, ret+4(FP)
 	RET

 // func mach_semaphore_timedwait(sema, sec, nsec uint32) int32
 TEXT runtime·mach_semaphore_timedwait(SB),NOSPLIT,$0
 	MOVL	$-38, AX
 	CALL	runtime·sysenter(SB)
 	MOVL	AX, ret+12(FP)
 	RET

 // func mach_semaphore_signal(sema uint32) int32
 TEXT runtime·mach_semaphore_signal(SB),NOSPLIT,$0
 	MOVL	$-33, AX
 	CALL	runtime·sysenter(SB)
 	MOVL	AX, ret+4(FP)
 	RET

 // func mach_semaphore_signal_all(sema uint32) int32
 TEXT runtime·mach_semaphore_signal_all(SB),NOSPLIT,$0
 	MOVL	$-34, AX
 	CALL	runtime·sysenter(SB)
 	MOVL	AX, ret+4(FP)
 	RET

 // func setldt(entry int, address int, limit int)
 // entry and limit are ignored.
 TEXT runtime·setldt(SB),NOSPLIT,$32
 	MOVL	address+4(FP), BX	// aka base

 	/*
 	 * When linking against the system libraries,
 	 * we use its pthread_create and let it set up %gs
 	 * for us.  When we do that, the private storage
 	 * we get is not at 0(GS) but at 0x468(GS).
 	 * 8l rewrites 0(TLS) into 0x468(GS) for us.
 	 * To accommodate that rewrite, we translate the
 	 * address and limit here so that 0x468(GS) maps to 0(address).
 	 *
 	 * See cgo/gcc_darwin_386.c:/468 for the derivation
 	 * of the constant.
 	 */
 	SUBL	$0x468, BX

 	/*
 	 * Must set up as USER_CTHREAD segment because
 	 * Darwin forces that value into %gs for signal handlers,
 	 * and if we don't set one up, we'll get a recursive
 	 * fault trying to get into the signal handler.
 	 * Since we have to set one up anyway, it might as
 	 * well be the value we want.  So don't bother with
 	 * i386_set_ldt.
 	 */
 	MOVL	BX, 4(SP)
 	MOVL	$3, AX	// thread_fast_set_cthread_self - machdep call #3
 	INT	$0x82	// sic: 0x82, not 0x80, for machdep call

 	XORL	AX, AX
 	MOVW	GS, AX
 	RET

 TEXT runtime·sysctl(SB),NOSPLIT,$0
 	MOVL	$202, AX
 	INT	$0x80
 	JAE	4(PC)
 	NEGL	AX
 	MOVL	AX, ret+24(FP)
 	RET
 	MOVL	$0, AX
 	MOVL	AX, ret+24(FP)
 	RET

 // func kqueue() int32
 TEXT runtime·kqueue(SB),NOSPLIT,$0
 	MOVL	$362, AX
 	INT	$0x80
 	JAE	2(PC)
 	NEGL	AX
 	MOVL	AX, ret+0(FP)
 	RET

 // func kevent(kq int32, ch *keventt, nch int32, ev *keventt, nev int32, ts *timespec) int32
 TEXT runtime·kevent(SB),NOSPLIT,$0
 	MOVL	$363, AX
 	INT	$0x80
 	JAE	2(PC)
 	NEGL	AX
 	MOVL	AX, ret+24(FP)
 	RET

 // func closeonexec(fd int32)
 TEXT runtime·closeonexec(SB),NOSPLIT,$32
 	MOVL	$92, AX  // fcntl
 	// 0(SP) is where the caller PC would be; kernel skips it
 	MOVL	fd+0(FP), BX
 	MOVL	BX, 4(SP)  // fd
 	MOVL	$2, 8(SP)  // F_SETFD
 	MOVL	$1, 12(SP)  // FD_CLOEXEC
 	INT	$0x80
 	JAE	2(PC)
 	NEGL	AX
 	RET
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// System calls and other sys.stuff for 386, Darwin
	// See http://fxr.watson.org/fxr/source/bsd/kern/syscalls.c?v=xnu-1228
	// or /usr/include/sys/syscall.h (on a Mac) for system call numbers.

	#include "go_asm.h"
	#include "go_tls.h"
	#include "textflag.h"

	// Exit the entire program (like C exit)
	TEXT runtime·exit(SB),NOSPLIT,$0
	MOVL $1, AX
	INT $0x80
	MOVL $0xf1, 0xf1 // crash
	RET

	// Exit this OS thread (like pthread_exit, which eventually
	// calls __bsdthread_terminate).
	TEXT runtime·exit1(SB),NOSPLIT,$0
	MOVL $361, AX
	INT $0x80
	JAE 2(PC)
	MOVL $0xf1, 0xf1 // crash
	RET

	TEXT runtime·open(SB),NOSPLIT,$0
	MOVL $5, AX
	INT $0x80
	JAE 2(PC)
	MOVL $-1, AX
	MOVL AX, ret+12(FP)
	RET

	TEXT runtime·closefd(SB),NOSPLIT,$0
	MOVL $6, AX
	INT $0x80
	JAE 2(PC)
	MOVL $-1, AX
	MOVL AX, ret+4(FP)
	RET

	TEXT runtime·read(SB),NOSPLIT,$0
	MOVL $3, AX
	INT $0x80
	JAE 2(PC)
	MOVL $-1, AX
	MOVL AX, ret+12(FP)
	RET

	TEXT runtime·write(SB),NOSPLIT,$0
	MOVL $4, AX
	INT $0x80
	JAE 2(PC)
	MOVL $-1, AX
	MOVL AX, ret+12(FP)
	RET

	TEXT runtime·raise(SB),NOSPLIT,$0
	// Ideally we'd send the signal to the current thread,
	// not the whole process, but that's too hard on OS X.
	JMP runtime·raiseproc(SB)

	TEXT runtime·raiseproc(SB),NOSPLIT,$16
	MOVL $20, AX // getpid
	INT $0x80
	MOVL AX, 4(SP) // pid
	MOVL sig+0(FP), AX
	MOVL AX, 8(SP) // signal
	MOVL $1, 12(SP) // posix
	MOVL $37, AX // kill
	INT $0x80
	RET

	TEXT runtime·mmap(SB),NOSPLIT,$0
	MOVL $197, AX
	INT $0x80
	MOVL AX, ret+24(FP)
	RET

	TEXT runtime·madvise(SB),NOSPLIT,$0
	MOVL $75, AX
	INT $0x80
	// ignore failure - maybe pages are locked
	RET

	TEXT runtime·munmap(SB),NOSPLIT,$0
	MOVL $73, AX
	INT $0x80
	JAE 2(PC)
	MOVL $0xf1, 0xf1 // crash
	RET

	TEXT runtime·setitimer(SB),NOSPLIT,$0
	MOVL $83, AX
	INT $0x80
	RET

	// OS X comm page time offsets
	// http://www.opensource.apple.com/source/xnu/xnu-1699.26.8/osfmk/i386/cpu_capabilities.h
	#define cpu_capabilities 0x20
	#define nt_tsc_base 0x50
	#define nt_scale 0x58
	#define nt_shift 0x5c
	#define nt_ns_base 0x60
	#define nt_generation 0x68
	#define gtod_generation 0x6c
	#define gtod_ns_base 0x70
	#define gtod_sec_base 0x78

	// called from assembly
	// 64-bit unix nanoseconds returned in DX:AX.
	// I'd much rather write this in C but we need
	// assembly for the 96-bit multiply and RDTSC.
	TEXT runtime·now(SB),NOSPLIT,$40
	MOVL $0xffff0000, BP /* comm page base */

	// Test for slow CPU. If so, the math is completely
	// different, and unimplemented here, so use the
	// system call.
	MOVL cpu_capabilities(BP), AX
	TESTL $0x4000, AX
	JNZ systime

	// Loop trying to take a consistent snapshot
	// of the time parameters.
	timeloop:
	MOVL gtod_generation(BP), BX
	TESTL BX, BX
	JZ systime
	MOVL nt_generation(BP), CX
	TESTL CX, CX
	JZ timeloop
	RDTSC
	MOVL nt_tsc_base(BP), SI
	MOVL (nt_tsc_base+4)(BP), DI
	MOVL SI, 0(SP)
	MOVL DI, 4(SP)
	MOVL nt_scale(BP), SI
	MOVL SI, 8(SP)
	MOVL nt_ns_base(BP), SI
	MOVL (nt_ns_base+4)(BP), DI
	MOVL SI, 12(SP)
	MOVL DI, 16(SP)
	CMPL nt_generation(BP), CX
	JNE timeloop
	MOVL gtod_ns_base(BP), SI
	MOVL (gtod_ns_base+4)(BP), DI
	MOVL SI, 20(SP)
	MOVL DI, 24(SP)
	MOVL gtod_sec_base(BP), SI
	MOVL (gtod_sec_base+4)(BP), DI
	MOVL SI, 28(SP)
	MOVL DI, 32(SP)
	CMPL gtod_generation(BP), BX
	JNE timeloop

	// Gathered all the data we need. Compute time.
	// ((tsc - nt_tsc_base) * nt_scale) >> 32 + nt_ns_base - gtod_ns_base + gtod_sec_base*1e9
	// The multiply and shift extracts the top 64 bits of the 96-bit product.
	SUBL 0(SP), AX // DX:AX = (tsc - nt_tsc_base)
	SBBL 4(SP), DX

	// We have x = tsc - nt_tsc_base - DX:AX to be
	// multiplied by y = nt_scale = 8(SP), keeping the top 64 bits of the 96-bit product.
	// xy = (x&0xffffffff)y + (x&0xffffffff00000000)*y
	// (xy)>>32 = ((x&0xffffffff)y)>>32 + (x>>32)*y
	MOVL DX, CX // SI = (x&0xffffffff)*y >> 32
	MOVL $0, DX
	MULL 8(SP)
	MOVL DX, SI

	MOVL CX, AX // DX:AX = (x>>32)*y
	MOVL $0, DX
	MULL 8(SP)

	ADDL SI, AX // DX:AX += (x&0xffffffff)*y >> 32
	ADCL $0, DX

	// DX:AX is now ((tsc - nt_tsc_base) * nt_scale) >> 32.
	ADDL 12(SP), AX // DX:AX += nt_ns_base
	ADCL 16(SP), DX
	SUBL 20(SP), AX // DX:AX -= gtod_ns_base
	SBBL 24(SP), DX
	MOVL AX, SI // DI:SI = DX:AX
	MOVL DX, DI
	MOVL 28(SP), AX // DX:AX = gtod_sec_base*1e9
	MOVL 32(SP), DX
	MOVL $1000000000, CX
	MULL CX
	ADDL SI, AX // DX:AX += DI:SI
	ADCL DI, DX
	RET

	systime:
	// Fall back to system call (usually first call in this thread)
	LEAL 16(SP), AX // must be non-nil, unused
	MOVL AX, 4(SP)
	MOVL $0, 8(SP) // time zone pointer
	MOVL $0, 12(SP) // required as of Sierra; Issue 16570
	MOVL $116, AX // SYS_GETTIMEOFDAY
	INT $0x80
	CMPL AX, $0
	JNE inreg
	MOVL 16(SP), AX
	MOVL 20(SP), DX
	inreg:
	// sec is in AX, usec in DX
	// convert to DX:AX nsec
	MOVL DX, BX
	MOVL $1000000000, CX
	MULL CX
	IMULL $1000, BX
	ADDL BX, AX
	ADCL $0, DX
	RET

	// func now() (sec int64, nsec int32)
	TEXT time·now(SB),NOSPLIT,$0
	CALL runtime·now(SB)
	MOVL $1000000000, CX
	DIVL CX
	MOVL AX, sec+0(FP)
	MOVL $0, sec+4(FP)
	MOVL DX, nsec+8(FP)
	RET

	// func nanotime() int64
	TEXT runtime·nanotime(SB),NOSPLIT,$0
	CALL runtime·now(SB)
	MOVL AX, ret_lo+0(FP)
	MOVL DX, ret_hi+4(FP)
	RET

	TEXT runtime·sigprocmask(SB),NOSPLIT,$0
	MOVL $329, AX // pthread_sigmask (on OS X, sigprocmask==entire process)
	INT $0x80
	JAE 2(PC)
	MOVL $0xf1, 0xf1 // crash
	RET

	TEXT runtime·sigaction(SB),NOSPLIT,$0
	MOVL $46, AX
	INT $0x80
	JAE 2(PC)
	MOVL $0xf1, 0xf1 // crash
	RET

	TEXT runtime·sigfwd(SB),NOSPLIT,$0-16
	MOVL fn+0(FP), AX
	MOVL sig+4(FP), BX
	MOVL info+8(FP), CX
	MOVL ctx+12(FP), DX
	MOVL SP, SI
	SUBL $32, SP
	ANDL $~15, SP // align stack: handler might be a C function
	MOVL BX, 0(SP)
	MOVL CX, 4(SP)
	MOVL DX, 8(SP)
	MOVL SI, 12(SP) // save SI: handler might be a Go function
	CALL AX
	MOVL 12(SP), AX
	MOVL AX, SP
	RET

	// Sigtramp's job is to call the actual signal handler.
	// It is called with the following arguments on the stack:
	// 0(SP) "return address" - ignored
	// 4(SP) actual handler
	// 8(SP) siginfo style
	// 12(SP) signal number
	// 16(SP) siginfo
	// 20(SP) context
	TEXT runtime·sigtramp(SB),NOSPLIT,$20
	MOVL sig+8(FP), BX
	MOVL BX, 0(SP)
	MOVL info+12(FP), BX
	MOVL BX, 4(SP)
	MOVL ctx+16(FP), BX
	MOVL BX, 8(SP)
	CALL runtime·sigtrampgo(SB)

	// call sigreturn
	MOVL ctx+16(FP), CX
	MOVL infostyle+4(FP), BX
	MOVL $0, 0(SP) // "caller PC" - ignored
	MOVL CX, 4(SP)
	MOVL BX, 8(SP)
	MOVL $184, AX // sigreturn(ucontext, infostyle)
	INT $0x80
	MOVL $0xf1, 0xf1 // crash
	RET

	TEXT runtime·sigaltstack(SB),NOSPLIT,$0
	MOVL $53, AX
	INT $0x80
	JAE 2(PC)
	MOVL $0xf1, 0xf1 // crash
	RET

	TEXT runtime·usleep(SB),NOSPLIT,$32
	MOVL $0, DX
	MOVL usec+0(FP), AX
	MOVL $1000000, CX
	DIVL CX
	MOVL AX, 24(SP) // sec
	MOVL DX, 28(SP) // usec

	// select(0, 0, 0, 0, &tv)
	MOVL $0, 0(SP) // "return PC" - ignored
	MOVL $0, 4(SP)
	MOVL $0, 8(SP)
	MOVL $0, 12(SP)
	MOVL $0, 16(SP)
	LEAL 24(SP), AX
	MOVL AX, 20(SP)
	MOVL $93, AX
	INT $0x80
	RET

	// func bsdthread_create(stk, arg unsafe.Pointer, fn uintptr) int32
	// System call args are: func arg stack pthread flags.
	TEXT runtime·bsdthread_create(SB),NOSPLIT,$32
	MOVL $360, AX
	// 0(SP) is where the caller PC would be; kernel skips it
	MOVL fn+8(FP), BX
	MOVL BX, 4(SP) // func
	MOVL arg+4(FP), BX
	MOVL BX, 8(SP) // arg
	MOVL stk+0(FP), BX
	MOVL BX, 12(SP) // stack
	MOVL $0, 16(SP) // pthread
	MOVL $0x1000000, 20(SP) // flags = PTHREAD_START_CUSTOM
	INT $0x80
	JAE 4(PC)
	NEGL AX
	MOVL AX, ret+12(FP)
	RET
	MOVL $0, AX
	MOVL AX, ret+12(FP)
	RET

	// The thread that bsdthread_create creates starts executing here,
	// because we registered this function using bsdthread_register
	// at startup.
	// AX = "pthread" (= 0x0)
	// BX = mach thread port
	// CX = "func" (= fn)
	// DX = "arg" (= m)
	// DI = stack top
	// SI = flags (= 0x1000000)
	// SP = stack - C_32_STK_ALIGN
	TEXT runtime·bsdthread_start(SB),NOSPLIT,$0
	// set up ldt 7+id to point at m->tls.
	LEAL m_tls(DX), BP
	MOVL m_id(DX), DI
	ADDL $7, DI // m0 is LDT#7. count up.
	// setldt(tls#, &tls, sizeof tls)
	PUSHAL // save registers
	PUSHL $32 // sizeof tls
	PUSHL BP // &tls
	PUSHL DI // tls #
	CALL runtime·setldt(SB)
	POPL AX
	POPL AX
	POPL AX
	POPAL

	// Now segment is established. Initialize m, g.
	get_tls(BP)
	MOVL m_g0(DX), AX
	MOVL AX, g(BP)
	MOVL DX, g_m(AX)
	MOVL BX, m_procid(DX) // m->procid = thread port (for debuggers)
	CALL runtime·stackcheck(SB) // smashes AX
	CALL CX // fn()
	CALL runtime·exit1(SB)
	RET

	// func bsdthread_register() int32
	// registers callbacks for threadstart (see bsdthread_create above
	// and wqthread and pthsize (not used). returns 0 on success.
	TEXT runtime·bsdthread_register(SB),NOSPLIT,$40
	MOVL $366, AX
	// 0(SP) is where kernel expects caller PC; ignored
	MOVL $runtime·bsdthread_start(SB), 4(SP) // threadstart
	MOVL $0, 8(SP) // wqthread, not used by us
	MOVL $0, 12(SP) // pthsize, not used by us
	MOVL $0, 16(SP) // dummy_value [sic]
	MOVL $0, 20(SP) // targetconc_ptr
	MOVL $0, 24(SP) // dispatchqueue_offset
	INT $0x80
	JAE 4(PC)
	NEGL AX
	MOVL AX, ret+0(FP)
	RET
	MOVL $0, AX
	MOVL AX, ret+0(FP)
	RET

	// Invoke Mach system call.
	// Assumes system call number in AX,
	// caller PC on stack, caller's caller PC next,
	// and then the system call arguments.
	//
	// Can be used for BSD too, but we don't,
	// because if you use this interface the BSD
	// system call numbers need an extra field
	// in the high 16 bits that seems to be the
	// argument count in bytes but is not always.
	// INT $0x80 works fine for those.
	TEXT runtime·sysenter(SB),NOSPLIT,$0
	POPL DX
	MOVL SP, CX
	BYTE $0x0F; BYTE $0x34; // SYSENTER
	// returns to DX with SP set to CX

	TEXT runtime·mach_msg_trap(SB),NOSPLIT,$0
	MOVL $-31, AX
	CALL runtime·sysenter(SB)
	MOVL AX, ret+28(FP)
	RET

	TEXT runtime·mach_reply_port(SB),NOSPLIT,$0
	MOVL $-26, AX
	CALL runtime·sysenter(SB)
	MOVL AX, ret+0(FP)
	RET

	TEXT runtime·mach_task_self(SB),NOSPLIT,$0
	MOVL $-28, AX
	CALL runtime·sysenter(SB)
	MOVL AX, ret+0(FP)
	RET

	// Mach provides trap versions of the semaphore ops,
	// instead of requiring the use of RPC.

	// func mach_semaphore_wait(sema uint32) int32
	TEXT runtime·mach_semaphore_wait(SB),NOSPLIT,$0
	MOVL $-36, AX
	CALL runtime·sysenter(SB)
	MOVL AX, ret+4(FP)
	RET

	// func mach_semaphore_timedwait(sema, sec, nsec uint32) int32
	TEXT runtime·mach_semaphore_timedwait(SB),NOSPLIT,$0
	MOVL $-38, AX
	CALL runtime·sysenter(SB)
	MOVL AX, ret+12(FP)
	RET

	// func mach_semaphore_signal(sema uint32) int32
	TEXT runtime·mach_semaphore_signal(SB),NOSPLIT,$0
	MOVL $-33, AX
	CALL runtime·sysenter(SB)
	MOVL AX, ret+4(FP)
	RET

	// func mach_semaphore_signal_all(sema uint32) int32
	TEXT runtime·mach_semaphore_signal_all(SB),NOSPLIT,$0
	MOVL $-34, AX
	CALL runtime·sysenter(SB)
	MOVL AX, ret+4(FP)
	RET

	// func setldt(entry int, address int, limit int)
	// entry and limit are ignored.
	TEXT runtime·setldt(SB),NOSPLIT,$32
	MOVL address+4(FP), BX // aka base

	/*
	* When linking against the system libraries,
	* we use its pthread_create and let it set up %gs
	* for us. When we do that, the private storage
	* we get is not at 0(GS) but at 0x468(GS).
	* 8l rewrites 0(TLS) into 0x468(GS) for us.
	* To accommodate that rewrite, we translate the
	* address and limit here so that 0x468(GS) maps to 0(address).
	*
	* See cgo/gcc_darwin_386.c:/468 for the derivation
	* of the constant.
	*/
	SUBL $0x468, BX

	/*
	* Must set up as USER_CTHREAD segment because
	* Darwin forces that value into %gs for signal handlers,
	* and if we don't set one up, we'll get a recursive
	* fault trying to get into the signal handler.
	* Since we have to set one up anyway, it might as
	* well be the value we want. So don't bother with
	* i386_set_ldt.
	*/
	MOVL BX, 4(SP)
	MOVL $3, AX // thread_fast_set_cthread_self - machdep call #3
	INT $0x82 // sic: 0x82, not 0x80, for machdep call

	XORL AX, AX
	MOVW GS, AX
	RET

	TEXT runtime·sysctl(SB),NOSPLIT,$0
	MOVL $202, AX
	INT $0x80
	JAE 4(PC)
	NEGL AX
	MOVL AX, ret+24(FP)
	RET
	MOVL $0, AX
	MOVL AX, ret+24(FP)
	RET

	// func kqueue() int32
	TEXT runtime·kqueue(SB),NOSPLIT,$0
	MOVL $362, AX
	INT $0x80
	JAE 2(PC)
	NEGL AX
	MOVL AX, ret+0(FP)
	RET

	// func kevent(kq int32, ch keventt, nch int32, ev keventt, nev int32, ts *timespec) int32
	TEXT runtime·kevent(SB),NOSPLIT,$0
	MOVL $363, AX
	INT $0x80
	JAE 2(PC)
	NEGL AX
	MOVL AX, ret+24(FP)
	RET

	// func closeonexec(fd int32)
	TEXT runtime·closeonexec(SB),NOSPLIT,$32
	MOVL $92, AX // fcntl
	// 0(SP) is where the caller PC would be; kernel skips it
	MOVL fd+0(FP), BX
	MOVL BX, 4(SP) // fd
	MOVL $2, 8(SP) // F_SETFD
	MOVL $1, 12(SP) // FD_CLOEXEC
	INT $0x80
	JAE 2(PC)
	NEGL AX
	RET