libgo/go/runtime/runtime1.go - gofrontend - 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.

 package runtime

 import (
 	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
 )

 // For gccgo, while we still have C runtime code, use go:linkname to
 // rename some functions to themselves, so that the compiler will
 // export them.
 //
 //go:linkname gotraceback runtime.gotraceback
 //go:linkname args runtime.args
 //go:linkname goargs runtime.goargs
 //go:linkname check runtime.check
 //go:linkname goenvs_unix runtime.goenvs_unix
 //go:linkname parsedebugvars runtime.parsedebugvars
 //go:linkname timediv runtime.timediv

 // Keep a cached value to make gotraceback fast,
 // since we call it on every call to gentraceback.
 // The cached value is a uint32 in which the low bits
 // are the "crash" and "all" settings and the remaining
 // bits are the traceback value (0 off, 1 on, 2 include system).
 const (
 	tracebackCrash = 1 << iota
 	tracebackAll
 	tracebackShift = iota
 )

 var traceback_cache uint32 = 2 << tracebackShift
 var traceback_env uint32

 // gotraceback returns the current traceback settings.
 //
 // If level is 0, suppress all tracebacks.
 // If level is 1, show tracebacks, but exclude runtime frames.
 // If level is 2, show tracebacks including runtime frames.
 // If all is set, print all goroutine stacks. Otherwise, print just the current goroutine.
 // If crash is set, crash (core dump, etc) after tracebacking.
 //
 //go:nosplit
 func gotraceback() (level int32, all, crash bool) {
 	_g_ := getg()
 	t := atomic.Load(&traceback_cache)
 	crash = t&tracebackCrash != 0
 	all = _g_.m.throwing > 0 || t&tracebackAll != 0
 	if _g_.m.traceback != 0 {
 		level = int32(_g_.m.traceback)
 	} else {
 		level = int32(t >> tracebackShift)
 	}
 	return
 }

 var (
 	argc int32
 	argv **byte
 )

 // nosplit for use in linux startup sysargs
 //go:nosplit
 func argv_index(argv **byte, i int32) *byte {
 	return *(**byte)(add(unsafe.Pointer(argv), uintptr(i)*sys.PtrSize))
 }

 func args(c int32, v **byte) {
 	argc = c
 	argv = v
 	sysargs(c, v)
 }

 func goargs() {
 	if GOOS == "windows" {
 		return
 	}
 	argslice = make([]string, argc)
 	for i := int32(0); i < argc; i++ {
 		argslice[i] = gostringnocopy(argv_index(argv, i))
 	}
 }

 func goenvs_unix() {
 	// TODO(austin): ppc64 in dynamic linking mode doesn't
 	// guarantee env[] will immediately follow argv. Might cause
 	// problems.
 	n := int32(0)
 	for argv_index(argv, argc+1+n) != nil {
 		n++
 	}

 	envs = make([]string, n)
 	for i := int32(0); i < n; i++ {
 		envs[i] = gostring(argv_index(argv, argc+1+i))
 	}
 }

 func environ() []string {
 	return envs
 }

 // TODO: These should be locals in testAtomic64, but we don't 8-byte
 // align stack variables on 386.
 var test_z64, test_x64 uint64

 func testAtomic64() {
 	test_z64 = 42
 	test_x64 = 0
 	if atomic.Cas64(&test_z64, test_x64, 1) {
 		throw("cas64 failed")
 	}
 	if test_x64 != 0 {
 		throw("cas64 failed")
 	}
 	test_x64 = 42
 	if !atomic.Cas64(&test_z64, test_x64, 1) {
 		throw("cas64 failed")
 	}
 	if test_x64 != 42 || test_z64 != 1 {
 		throw("cas64 failed")
 	}
 	if atomic.Load64(&test_z64) != 1 {
 		throw("load64 failed")
 	}
 	atomic.Store64(&test_z64, (1<<40)+1)
 	if atomic.Load64(&test_z64) != (1<<40)+1 {
 		throw("store64 failed")
 	}
 	if atomic.Xadd64(&test_z64, (1<<40)+1) != (2<<40)+2 {
 		throw("xadd64 failed")
 	}
 	if atomic.Load64(&test_z64) != (2<<40)+2 {
 		throw("xadd64 failed")
 	}
 	if atomic.Xchg64(&test_z64, (3<<40)+3) != (2<<40)+2 {
 		throw("xchg64 failed")
 	}
 	if atomic.Load64(&test_z64) != (3<<40)+3 {
 		throw("xchg64 failed")
 	}
 }

 func check() {
 	var (
 		a     int8
 		b     uint8
 		c     int16
 		d     uint16
 		e     int32
 		f     uint32
 		g     int64
 		h     uint64
 		i, i1 float32
 		j, j1 float64
 		k, k1 unsafe.Pointer
 		l     *uint16
 		m     [4]byte
 	)
 	type x1t struct {
 		x uint8
 	}
 	type y1t struct {
 		x1 x1t
 		y  uint8
 	}
 	var x1 x1t
 	var y1 y1t

 	if unsafe.Sizeof(a) != 1 {
 		throw("bad a")
 	}
 	if unsafe.Sizeof(b) != 1 {
 		throw("bad b")
 	}
 	if unsafe.Sizeof(c) != 2 {
 		throw("bad c")
 	}
 	if unsafe.Sizeof(d) != 2 {
 		throw("bad d")
 	}
 	if unsafe.Sizeof(e) != 4 {
 		throw("bad e")
 	}
 	if unsafe.Sizeof(f) != 4 {
 		throw("bad f")
 	}
 	if unsafe.Sizeof(g) != 8 {
 		throw("bad g")
 	}
 	if unsafe.Sizeof(h) != 8 {
 		throw("bad h")
 	}
 	if unsafe.Sizeof(i) != 4 {
 		throw("bad i")
 	}
 	if unsafe.Sizeof(j) != 8 {
 		throw("bad j")
 	}
 	if unsafe.Sizeof(k) != sys.PtrSize {
 		throw("bad k")
 	}
 	if unsafe.Sizeof(l) != sys.PtrSize {
 		throw("bad l")
 	}
 	if unsafe.Sizeof(x1) != 1 {
 		throw("bad unsafe.Sizeof x1")
 	}
 	if unsafe.Offsetof(y1.y) != 1 {
 		throw("bad offsetof y1.y")
 	}
 	if unsafe.Sizeof(y1) != 2 {
 		throw("bad unsafe.Sizeof y1")
 	}

 	if timediv(12345*1000000000+54321, 1000000000, &e) != 12345 || e != 54321 {
 		throw("bad timediv")
 	}

 	var z uint32
 	z = 1
 	if !atomic.Cas(&z, 1, 2) {
 		throw("cas1")
 	}
 	if z != 2 {
 		throw("cas2")
 	}

 	z = 4
 	if atomic.Cas(&z, 5, 6) {
 		throw("cas3")
 	}
 	if z != 4 {
 		throw("cas4")
 	}

 	z = 0xffffffff
 	if !atomic.Cas(&z, 0xffffffff, 0xfffffffe) {
 		throw("cas5")
 	}
 	if z != 0xfffffffe {
 		throw("cas6")
 	}

 	k = unsafe.Pointer(uintptr(0xfedcb123))
 	if sys.PtrSize == 8 {
 		k = unsafe.Pointer(uintptr(k) << 10)
 	}
 	if casp(&k, nil, nil) {
 		throw("casp1")
 	}
 	k1 = add(k, 1)
 	if !casp(&k, k, k1) {
 		throw("casp2")
 	}
 	if k != k1 {
 		throw("casp3")
 	}

 	m = [4]byte{1, 1, 1, 1}
 	atomic.Or8(&m[1], 0xf0)
 	if m[0] != 1 || m[1] != 0xf1 || m[2] != 1 || m[3] != 1 {
 		throw("atomicor8")
 	}

 	m = [4]byte{0xff, 0xff, 0xff, 0xff}
 	atomic.And8(&m[1], 0x1)
 	if m[0] != 0xff || m[1] != 0x1 || m[2] != 0xff || m[3] != 0xff {
 		throw("atomicand8")
 	}

 	*(*uint64)(unsafe.Pointer(&j)) = ^uint64(0)
 	if j == j {
 		throw("float64nan")
 	}
 	if !(j != j) {
 		throw("float64nan1")
 	}

 	*(*uint64)(unsafe.Pointer(&j1)) = ^uint64(1)
 	if j == j1 {
 		throw("float64nan2")
 	}
 	if !(j != j1) {
 		throw("float64nan3")
 	}

 	*(*uint32)(unsafe.Pointer(&i)) = ^uint32(0)
 	if i == i {
 		throw("float32nan")
 	}
 	if i == i {
 		throw("float32nan1")
 	}

 	*(*uint32)(unsafe.Pointer(&i1)) = ^uint32(1)
 	if i == i1 {
 		throw("float32nan2")
 	}
 	if i == i1 {
 		throw("float32nan3")
 	}

 	testAtomic64()

 	// if _FixedStack != round2(_FixedStack) {
 	// 	throw("FixedStack is not power-of-2")
 	// }

 	if !checkASM() {
 		throw("assembly checks failed")
 	}
 }

 type dbgVar struct {
 	name  string
 	value *int32
 }

 // Holds variables parsed from GODEBUG env var,
 // except for "memprofilerate" since there is an
 // existing int var for that value, which may
 // already have an initial value.
 var debug struct {
 	allocfreetrace     int32
 	cgocheck           int32
 	efence             int32
 	gccheckmark        int32
 	gcpacertrace       int32
 	gcshrinkstackoff   int32
 	gcrescanstacks     int32
 	gcstoptheworld     int32
 	gctrace            int32
 	invalidptr         int32
 	sbrk               int32
 	scavenge           int32
 	scheddetail        int32
 	schedtrace         int32
 	tracebackancestors int32
 }

 var dbgvars = []dbgVar{
 	{"allocfreetrace", &debug.allocfreetrace},
 	{"cgocheck", &debug.cgocheck},
 	{"efence", &debug.efence},
 	{"gccheckmark", &debug.gccheckmark},
 	{"gcpacertrace", &debug.gcpacertrace},
 	{"gcshrinkstackoff", &debug.gcshrinkstackoff},
 	{"gcrescanstacks", &debug.gcrescanstacks},
 	{"gcstoptheworld", &debug.gcstoptheworld},
 	{"gctrace", &debug.gctrace},
 	{"invalidptr", &debug.invalidptr},
 	{"sbrk", &debug.sbrk},
 	{"scavenge", &debug.scavenge},
 	{"scheddetail", &debug.scheddetail},
 	{"schedtrace", &debug.schedtrace},
 	{"tracebackancestors", &debug.tracebackancestors},
 }

 func parsedebugvars() {
 	// defaults
 	debug.cgocheck = 1

 	// Unfortunately, because gccgo uses conservative stack scanning,
 	// we can not enable invalid pointer checking. It is possible for
 	// memory block M1 to point to M2, and for both to be dead.
 	// We release M2, causing the entire span to be released.
 	// Before we release M1, a stack pointer appears that point into it.
 	// This stack pointer is presumably dead, but causes M1 to be marked.
 	// We scan M1 and see the pointer to M2 on a released span.
 	// At that point, if debug.invalidptr is set, we crash.
 	// This is not a problem, assuming that M1 really is dead and
 	// the pointer we discovered to it will not be used.
 	// debug.invalidptr = 1

 	for p := gogetenv("GODEBUG"); p != ""; {
 		field := ""
 		i := index(p, ",")
 		if i < 0 {
 			field, p = p, ""
 		} else {
 			field, p = p[:i], p[i+1:]
 		}
 		i = index(field, "=")
 		if i < 0 {
 			continue
 		}
 		key, value := field[:i], field[i+1:]

 		// Update MemProfileRate directly here since it
 		// is int, not int32, and should only be updated
 		// if specified in GODEBUG.
 		if key == "memprofilerate" {
 			if n, ok := atoi(value); ok {
 				MemProfileRate = n
 			}
 		} else {
 			for _, v := range dbgvars {
 				if v.name == key {
 					if n, ok := atoi32(value); ok {
 						*v.value = n
 					}
 				}
 			}
 		}
 	}

 	setTraceback(gogetenv("GOTRACEBACK"))
 	traceback_env = traceback_cache
 }

 //go:linkname setTraceback runtime..z2fdebug.SetTraceback
 func setTraceback(level string) {
 	var t uint32
 	switch level {
 	case "none":
 		t = 0
 	case "single", "":
 		t = 1 << tracebackShift
 	case "all":
 		t = 1<<tracebackShift | tracebackAll
 	case "system":
 		t = 2<<tracebackShift | tracebackAll
 	case "crash":
 		t = 2<<tracebackShift | tracebackAll | tracebackCrash
 	default:
 		t = tracebackAll
 		if n, ok := atoi(level); ok && n == int(uint32(n)) {
 			t |= uint32(n) << tracebackShift
 		}
 	}
 	// when C owns the process, simply exit'ing the process on fatal errors
 	// and panics is surprising. Be louder and abort instead.
 	if islibrary || isarchive {
 		t |= tracebackCrash
 	}

 	t |= traceback_env

 	atomic.Store(&traceback_cache, t)
 }

 // Poor mans 64-bit division.
 // This is a very special function, do not use it if you are not sure what you are doing.
 // int64 division is lowered into _divv() call on 386, which does not fit into nosplit functions.
 // Handles overflow in a time-specific manner.
 //go:nosplit
 func timediv(v int64, div int32, rem *int32) int32 {
 	res := int32(0)
 	for bit := 30; bit >= 0; bit-- {
 		if v >= int64(div)<<uint(bit) {
 			v = v - (int64(div) << uint(bit))
 			res += 1 << uint(bit)
 		}
 	}
 	if v >= int64(div) {
 		if rem != nil {
 			*rem = 0
 		}
 		return 0x7fffffff
 	}
 	if rem != nil {
 		*rem = int32(v)
 	}
 	return res
 }

 // Helpers for Go. Must be NOSPLIT, must only call NOSPLIT functions, and must not block.

 //go:nosplit
 func acquirem() *m {
 	_g_ := getg()
 	_g_.m.locks++
 	return _g_.m
 }

 //go:nosplit
 func releasem(mp *m) {
 	// _g_ := getg()
 	mp.locks--
 	// if mp.locks == 0 && _g_.preempt {
 	//	// restore the preemption request in case we've cleared it in newstack
 	//	_g_.stackguard0 = stackPreempt
 	// }
 }

 //go:nosplit
 func gomcache() *mcache {
 	return getg().m.mcache
 }
	// 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.

	package runtime

	import (
	"runtime/internal/atomic"
	"runtime/internal/sys"
	"unsafe"
	)

	// For gccgo, while we still have C runtime code, use go:linkname to
	// rename some functions to themselves, so that the compiler will
	// export them.
	//
	//go:linkname gotraceback runtime.gotraceback
	//go:linkname args runtime.args
	//go:linkname goargs runtime.goargs
	//go:linkname check runtime.check
	//go:linkname goenvs_unix runtime.goenvs_unix
	//go:linkname parsedebugvars runtime.parsedebugvars
	//go:linkname timediv runtime.timediv

	// Keep a cached value to make gotraceback fast,
	// since we call it on every call to gentraceback.
	// The cached value is a uint32 in which the low bits
	// are the "crash" and "all" settings and the remaining
	// bits are the traceback value (0 off, 1 on, 2 include system).
	const (
	tracebackCrash = 1 << iota
	tracebackAll
	tracebackShift = iota
	)

	var traceback_cache uint32 = 2 << tracebackShift
	var traceback_env uint32

	// gotraceback returns the current traceback settings.
	//
	// If level is 0, suppress all tracebacks.
	// If level is 1, show tracebacks, but exclude runtime frames.
	// If level is 2, show tracebacks including runtime frames.
	// If all is set, print all goroutine stacks. Otherwise, print just the current goroutine.
	// If crash is set, crash (core dump, etc) after tracebacking.
	//
	//go:nosplit
	func gotraceback() (level int32, all, crash bool) {
	_g_ := getg()
	t := atomic.Load(&traceback_cache)
	crash = t&tracebackCrash != 0
	all = _g_.m.throwing > 0 \|\| t&tracebackAll != 0
	if _g_.m.traceback != 0 {
	level = int32(_g_.m.traceback)
	} else {
	level = int32(t >> tracebackShift)
	}
	return
	}

	var (
	argc int32
	argv **byte
	)

	// nosplit for use in linux startup sysargs
	//go:nosplit
	func argv_index(argv *byte, i int32) byte {
	return (byte)(add(unsafe.Pointer(argv), uintptr(i)sys.PtrSize))
	}

	func args(c int32, v **byte) {
	argc = c
	argv = v
	sysargs(c, v)
	}

	func goargs() {
	if GOOS == "windows" {
	return
	}
	argslice = make([]string, argc)
	for i := int32(0); i < argc; i++ {
	argslice[i] = gostringnocopy(argv_index(argv, i))
	}
	}

	func goenvs_unix() {
	// TODO(austin): ppc64 in dynamic linking mode doesn't
	// guarantee env[] will immediately follow argv. Might cause
	// problems.
	n := int32(0)
	for argv_index(argv, argc+1+n) != nil {
	n++
	}

	envs = make([]string, n)
	for i := int32(0); i < n; i++ {
	envs[i] = gostring(argv_index(argv, argc+1+i))
	}
	}

	func environ() []string {
	return envs
	}

	// TODO: These should be locals in testAtomic64, but we don't 8-byte
	// align stack variables on 386.
	var test_z64, test_x64 uint64

	func testAtomic64() {
	test_z64 = 42
	test_x64 = 0
	if atomic.Cas64(&test_z64, test_x64, 1) {
	throw("cas64 failed")
	}
	if test_x64 != 0 {
	throw("cas64 failed")
	}
	test_x64 = 42
	if !atomic.Cas64(&test_z64, test_x64, 1) {
	throw("cas64 failed")
	}
	if test_x64 != 42 \|\| test_z64 != 1 {
	throw("cas64 failed")
	}
	if atomic.Load64(&test_z64) != 1 {
	throw("load64 failed")
	}
	atomic.Store64(&test_z64, (1<<40)+1)
	if atomic.Load64(&test_z64) != (1<<40)+1 {
	throw("store64 failed")
	}
	if atomic.Xadd64(&test_z64, (1<<40)+1) != (2<<40)+2 {
	throw("xadd64 failed")
	}
	if atomic.Load64(&test_z64) != (2<<40)+2 {
	throw("xadd64 failed")
	}
	if atomic.Xchg64(&test_z64, (3<<40)+3) != (2<<40)+2 {
	throw("xchg64 failed")
	}
	if atomic.Load64(&test_z64) != (3<<40)+3 {
	throw("xchg64 failed")
	}
	}

	func check() {
	var (
	a int8
	b uint8
	c int16
	d uint16
	e int32
	f uint32
	g int64
	h uint64
	i, i1 float32
	j, j1 float64
	k, k1 unsafe.Pointer
	l *uint16
	m [4]byte
	)
	type x1t struct {
	x uint8
	}
	type y1t struct {
	x1 x1t
	y uint8
	}
	var x1 x1t
	var y1 y1t

	if unsafe.Sizeof(a) != 1 {
	throw("bad a")
	}
	if unsafe.Sizeof(b) != 1 {
	throw("bad b")
	}
	if unsafe.Sizeof(c) != 2 {
	throw("bad c")
	}
	if unsafe.Sizeof(d) != 2 {
	throw("bad d")
	}
	if unsafe.Sizeof(e) != 4 {
	throw("bad e")
	}
	if unsafe.Sizeof(f) != 4 {
	throw("bad f")
	}
	if unsafe.Sizeof(g) != 8 {
	throw("bad g")
	}
	if unsafe.Sizeof(h) != 8 {
	throw("bad h")
	}
	if unsafe.Sizeof(i) != 4 {
	throw("bad i")
	}
	if unsafe.Sizeof(j) != 8 {
	throw("bad j")
	}
	if unsafe.Sizeof(k) != sys.PtrSize {
	throw("bad k")
	}
	if unsafe.Sizeof(l) != sys.PtrSize {
	throw("bad l")
	}
	if unsafe.Sizeof(x1) != 1 {
	throw("bad unsafe.Sizeof x1")
	}
	if unsafe.Offsetof(y1.y) != 1 {
	throw("bad offsetof y1.y")
	}
	if unsafe.Sizeof(y1) != 2 {
	throw("bad unsafe.Sizeof y1")
	}

	if timediv(12345*1000000000+54321, 1000000000, &e) != 12345 \|\| e != 54321 {
	throw("bad timediv")
	}

	var z uint32
	z = 1
	if !atomic.Cas(&z, 1, 2) {
	throw("cas1")
	}
	if z != 2 {
	throw("cas2")
	}

	z = 4
	if atomic.Cas(&z, 5, 6) {
	throw("cas3")
	}
	if z != 4 {
	throw("cas4")
	}

	z = 0xffffffff
	if !atomic.Cas(&z, 0xffffffff, 0xfffffffe) {
	throw("cas5")
	}
	if z != 0xfffffffe {
	throw("cas6")
	}

	k = unsafe.Pointer(uintptr(0xfedcb123))
	if sys.PtrSize == 8 {
	k = unsafe.Pointer(uintptr(k) << 10)
	}
	if casp(&k, nil, nil) {
	throw("casp1")
	}
	k1 = add(k, 1)
	if !casp(&k, k, k1) {
	throw("casp2")
	}
	if k != k1 {
	throw("casp3")
	}

	m = [4]byte{1, 1, 1, 1}
	atomic.Or8(&m[1], 0xf0)
	if m[0] != 1 \|\| m[1] != 0xf1 \|\| m[2] != 1 \|\| m[3] != 1 {
	throw("atomicor8")
	}

	m = [4]byte{0xff, 0xff, 0xff, 0xff}
	atomic.And8(&m[1], 0x1)
	if m[0] != 0xff \|\| m[1] != 0x1 \|\| m[2] != 0xff \|\| m[3] != 0xff {
	throw("atomicand8")
	}

	(uint64)(unsafe.Pointer(&j)) = ^uint64(0)
	if j == j {
	throw("float64nan")
	}
	if !(j != j) {
	throw("float64nan1")
	}

	(uint64)(unsafe.Pointer(&j1)) = ^uint64(1)
	if j == j1 {
	throw("float64nan2")
	}
	if !(j != j1) {
	throw("float64nan3")
	}

	(uint32)(unsafe.Pointer(&i)) = ^uint32(0)
	if i == i {
	throw("float32nan")
	}
	if i == i {
	throw("float32nan1")
	}

	(uint32)(unsafe.Pointer(&i1)) = ^uint32(1)
	if i == i1 {
	throw("float32nan2")
	}
	if i == i1 {
	throw("float32nan3")
	}

	testAtomic64()

	// if _FixedStack != round2(_FixedStack) {
	// throw("FixedStack is not power-of-2")
	// }

	if !checkASM() {
	throw("assembly checks failed")
	}
	}

	type dbgVar struct {
	name string
	value *int32
	}

	// Holds variables parsed from GODEBUG env var,
	// except for "memprofilerate" since there is an
	// existing int var for that value, which may
	// already have an initial value.
	var debug struct {
	allocfreetrace int32
	cgocheck int32
	efence int32
	gccheckmark int32
	gcpacertrace int32
	gcshrinkstackoff int32
	gcrescanstacks int32
	gcstoptheworld int32
	gctrace int32
	invalidptr int32
	sbrk int32
	scavenge int32
	scheddetail int32
	schedtrace int32
	tracebackancestors int32
	}

	var dbgvars = []dbgVar{
	{"allocfreetrace", &debug.allocfreetrace},
	{"cgocheck", &debug.cgocheck},
	{"efence", &debug.efence},
	{"gccheckmark", &debug.gccheckmark},
	{"gcpacertrace", &debug.gcpacertrace},
	{"gcshrinkstackoff", &debug.gcshrinkstackoff},
	{"gcrescanstacks", &debug.gcrescanstacks},
	{"gcstoptheworld", &debug.gcstoptheworld},
	{"gctrace", &debug.gctrace},
	{"invalidptr", &debug.invalidptr},
	{"sbrk", &debug.sbrk},
	{"scavenge", &debug.scavenge},
	{"scheddetail", &debug.scheddetail},
	{"schedtrace", &debug.schedtrace},
	{"tracebackancestors", &debug.tracebackancestors},
	}

	func parsedebugvars() {
	// defaults
	debug.cgocheck = 1

	// Unfortunately, because gccgo uses conservative stack scanning,
	// we can not enable invalid pointer checking. It is possible for
	// memory block M1 to point to M2, and for both to be dead.
	// We release M2, causing the entire span to be released.
	// Before we release M1, a stack pointer appears that point into it.
	// This stack pointer is presumably dead, but causes M1 to be marked.
	// We scan M1 and see the pointer to M2 on a released span.
	// At that point, if debug.invalidptr is set, we crash.
	// This is not a problem, assuming that M1 really is dead and
	// the pointer we discovered to it will not be used.
	// debug.invalidptr = 1

	for p := gogetenv("GODEBUG"); p != ""; {
	field := ""
	i := index(p, ",")
	if i < 0 {
	field, p = p, ""
	} else {
	field, p = p[:i], p[i+1:]
	}
	i = index(field, "=")
	if i < 0 {
	continue
	}
	key, value := field[:i], field[i+1:]

	// Update MemProfileRate directly here since it
	// is int, not int32, and should only be updated
	// if specified in GODEBUG.
	if key == "memprofilerate" {
	if n, ok := atoi(value); ok {
	MemProfileRate = n
	}
	} else {
	for _, v := range dbgvars {
	if v.name == key {
	if n, ok := atoi32(value); ok {
	*v.value = n
	}
	}
	}
	}
	}

	setTraceback(gogetenv("GOTRACEBACK"))
	traceback_env = traceback_cache
	}

	//go:linkname setTraceback runtime..z2fdebug.SetTraceback
	func setTraceback(level string) {
	var t uint32
	switch level {
	case "none":
	t = 0
	case "single", "":
	t = 1 << tracebackShift
	case "all":
	t = 1<<tracebackShift \| tracebackAll
	case "system":
	t = 2<<tracebackShift \| tracebackAll
	case "crash":
	t = 2<<tracebackShift \| tracebackAll \| tracebackCrash
	default:
	t = tracebackAll
	if n, ok := atoi(level); ok && n == int(uint32(n)) {
	t \|= uint32(n) << tracebackShift
	}
	}
	// when C owns the process, simply exit'ing the process on fatal errors
	// and panics is surprising. Be louder and abort instead.
	if islibrary \|\| isarchive {
	t \|= tracebackCrash
	}

	t \|= traceback_env

	atomic.Store(&traceback_cache, t)
	}

	// Poor mans 64-bit division.
	// This is a very special function, do not use it if you are not sure what you are doing.
	// int64 division is lowered into _divv() call on 386, which does not fit into nosplit functions.
	// Handles overflow in a time-specific manner.
	//go:nosplit
	func timediv(v int64, div int32, rem *int32) int32 {
	res := int32(0)
	for bit := 30; bit >= 0; bit-- {
	if v >= int64(div)<<uint(bit) {
	v = v - (int64(div) << uint(bit))
	res += 1 << uint(bit)
	}
	}
	if v >= int64(div) {
	if rem != nil {
	*rem = 0
	}
	return 0x7fffffff
	}
	if rem != nil {
	*rem = int32(v)
	}
	return res
	}

	// Helpers for Go. Must be NOSPLIT, must only call NOSPLIT functions, and must not block.

	//go:nosplit
	func acquirem() *m {
	_g_ := getg()
	_g_.m.locks++
	return _g_.m
	}

	//go:nosplit
	func releasem(mp *m) {
	// _g_ := getg()
	mp.locks--
	// if mp.locks == 0 && _g_.preempt {
	// // restore the preemption request in case we've cleared it in newstack
	// _g_.stackguard0 = stackPreempt
	// }
	}

	//go:nosplit
	func gomcache() *mcache {
	return getg().m.mcache
	}