blob: 5f28d28757337fba9c93b9878ae80a1c6c0f53d4 [file] [log] [blame]
// Copyright 2013 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 "unsafe"
const (
// StackDebug == 0: no logging
// == 1: logging of per-stack operations
// == 2: logging of per-frame operations
// == 3: logging of per-word updates
// == 4: logging of per-word reads
stackDebug = 0
stackFromSystem = 0 // allocate stacks from system memory instead of the heap
stackFaultOnFree = 0 // old stacks are mapped noaccess to detect use after free
stackPoisonCopy = 0 // fill stack that should not be accessed with garbage, to detect bad dereferences during copy
stackCache = 1
)
const (
uintptrMask = 1<<(8*ptrSize) - 1
poisonStack = uintptrMask & 0x6868686868686868
// Goroutine preemption request.
// Stored into g->stackguard0 to cause split stack check failure.
// Must be greater than any real sp.
// 0xfffffade in hex.
stackPreempt = uintptrMask & -1314
// Thread is forking.
// Stored into g->stackguard0 to cause split stack check failure.
// Must be greater than any real sp.
stackFork = uintptrMask & -1234
)
// Global pool of spans that have free stacks.
// Stacks are assigned an order according to size.
// order = log_2(size/FixedStack)
// There is a free list for each order.
// TODO: one lock per order?
var stackpool [_NumStackOrders]mspan
var stackpoolmu mutex
var stackfreequeue stack
// Cached value of haveexperiment("framepointer")
var framepointer_enabled bool
func stackinit() {
if _StackCacheSize&_PageMask != 0 {
throw("cache size must be a multiple of page size")
}
for i := range stackpool {
mSpanList_Init(&stackpool[i])
}
}
// Allocates a stack from the free pool. Must be called with
// stackpoolmu held.
func stackpoolalloc(order uint8) gclinkptr {
list := &stackpool[order]
s := list.next
if s == list {
// no free stacks. Allocate another span worth.
s = mHeap_AllocStack(&mheap_, _StackCacheSize>>_PageShift)
if s == nil {
throw("out of memory")
}
if s.ref != 0 {
throw("bad ref")
}
if s.freelist.ptr() != nil {
throw("bad freelist")
}
for i := uintptr(0); i < _StackCacheSize; i += _FixedStack << order {
x := gclinkptr(uintptr(s.start)<<_PageShift + i)
x.ptr().next = s.freelist
s.freelist = x
}
mSpanList_Insert(list, s)
}
x := s.freelist
if x.ptr() == nil {
throw("span has no free stacks")
}
s.freelist = x.ptr().next
s.ref++
if s.freelist.ptr() == nil {
// all stacks in s are allocated.
mSpanList_Remove(s)
}
return x
}
// Adds stack x to the free pool. Must be called with stackpoolmu held.
func stackpoolfree(x gclinkptr, order uint8) {
s := mHeap_Lookup(&mheap_, (unsafe.Pointer)(x))
if s.state != _MSpanStack {
throw("freeing stack not in a stack span")
}
if s.freelist.ptr() == nil {
// s will now have a free stack
mSpanList_Insert(&stackpool[order], s)
}
x.ptr().next = s.freelist
s.freelist = x
s.ref--
if s.ref == 0 {
// span is completely free - return to heap
mSpanList_Remove(s)
s.freelist = 0
mHeap_FreeStack(&mheap_, s)
}
}
// stackcacherefill/stackcacherelease implement a global pool of stack segments.
// The pool is required to prevent unlimited growth of per-thread caches.
func stackcacherefill(c *mcache, order uint8) {
if stackDebug >= 1 {
print("stackcacherefill order=", order, "\n")
}
// Grab some stacks from the global cache.
// Grab half of the allowed capacity (to prevent thrashing).
var list gclinkptr
var size uintptr
lock(&stackpoolmu)
for size < _StackCacheSize/2 {
x := stackpoolalloc(order)
x.ptr().next = list
list = x
size += _FixedStack << order
}
unlock(&stackpoolmu)
c.stackcache[order].list = list
c.stackcache[order].size = size
}
func stackcacherelease(c *mcache, order uint8) {
if stackDebug >= 1 {
print("stackcacherelease order=", order, "\n")
}
x := c.stackcache[order].list
size := c.stackcache[order].size
lock(&stackpoolmu)
for size > _StackCacheSize/2 {
y := x.ptr().next
stackpoolfree(x, order)
x = y
size -= _FixedStack << order
}
unlock(&stackpoolmu)
c.stackcache[order].list = x
c.stackcache[order].size = size
}
func stackcache_clear(c *mcache) {
if stackDebug >= 1 {
print("stackcache clear\n")
}
lock(&stackpoolmu)
for order := uint8(0); order < _NumStackOrders; order++ {
x := c.stackcache[order].list
for x.ptr() != nil {
y := x.ptr().next
stackpoolfree(x, order)
x = y
}
c.stackcache[order].list = 0
c.stackcache[order].size = 0
}
unlock(&stackpoolmu)
}
func stackalloc(n uint32) stack {
// Stackalloc must be called on scheduler stack, so that we
// never try to grow the stack during the code that stackalloc runs.
// Doing so would cause a deadlock (issue 1547).
thisg := getg()
if thisg != thisg.m.g0 {
throw("stackalloc not on scheduler stack")
}
if n&(n-1) != 0 {
throw("stack size not a power of 2")
}
if stackDebug >= 1 {
print("stackalloc ", n, "\n")
}
if debug.efence != 0 || stackFromSystem != 0 {
v := sysAlloc(round(uintptr(n), _PageSize), &memstats.stacks_sys)
if v == nil {
throw("out of memory (stackalloc)")
}
return stack{uintptr(v), uintptr(v) + uintptr(n)}
}
// Small stacks are allocated with a fixed-size free-list allocator.
// If we need a stack of a bigger size, we fall back on allocating
// a dedicated span.
var v unsafe.Pointer
if stackCache != 0 && n < _FixedStack<<_NumStackOrders && n < _StackCacheSize {
order := uint8(0)
n2 := n
for n2 > _FixedStack {
order++
n2 >>= 1
}
var x gclinkptr
c := thisg.m.mcache
if c == nil || thisg.m.preemptoff != "" || thisg.m.helpgc != 0 {
// c == nil can happen in the guts of exitsyscall or
// procresize. Just get a stack from the global pool.
// Also don't touch stackcache during gc
// as it's flushed concurrently.
lock(&stackpoolmu)
x = stackpoolalloc(order)
unlock(&stackpoolmu)
} else {
x = c.stackcache[order].list
if x.ptr() == nil {
stackcacherefill(c, order)
x = c.stackcache[order].list
}
c.stackcache[order].list = x.ptr().next
c.stackcache[order].size -= uintptr(n)
}
v = (unsafe.Pointer)(x)
} else {
s := mHeap_AllocStack(&mheap_, round(uintptr(n), _PageSize)>>_PageShift)
if s == nil {
throw("out of memory")
}
v = (unsafe.Pointer)(s.start << _PageShift)
}
if raceenabled {
racemalloc(v, uintptr(n))
}
if stackDebug >= 1 {
print(" allocated ", v, "\n")
}
return stack{uintptr(v), uintptr(v) + uintptr(n)}
}
func stackfree(stk stack) {
gp := getg()
n := stk.hi - stk.lo
v := (unsafe.Pointer)(stk.lo)
if n&(n-1) != 0 {
throw("stack not a power of 2")
}
if stackDebug >= 1 {
println("stackfree", v, n)
memclr(v, n) // for testing, clobber stack data
}
if debug.efence != 0 || stackFromSystem != 0 {
if debug.efence != 0 || stackFaultOnFree != 0 {
sysFault(v, n)
} else {
sysFree(v, n, &memstats.stacks_sys)
}
return
}
if stackCache != 0 && n < _FixedStack<<_NumStackOrders && n < _StackCacheSize {
order := uint8(0)
n2 := n
for n2 > _FixedStack {
order++
n2 >>= 1
}
x := gclinkptr(v)
c := gp.m.mcache
if c == nil || gp.m.preemptoff != "" || gp.m.helpgc != 0 {
lock(&stackpoolmu)
stackpoolfree(x, order)
unlock(&stackpoolmu)
} else {
if c.stackcache[order].size >= _StackCacheSize {
stackcacherelease(c, order)
}
x.ptr().next = c.stackcache[order].list
c.stackcache[order].list = x
c.stackcache[order].size += n
}
} else {
s := mHeap_Lookup(&mheap_, v)
if s.state != _MSpanStack {
println(hex(s.start<<_PageShift), v)
throw("bad span state")
}
mHeap_FreeStack(&mheap_, s)
}
}
var maxstacksize uintptr = 1 << 20 // enough until runtime.main sets it for real
var mapnames = []string{
typeDead: "---",
typeScalar: "scalar",
typePointer: "ptr",
}
// Stack frame layout
//
// (x86)
// +------------------+
// | args from caller |
// +------------------+ <- frame->argp
// | return address |
// +------------------+
// | caller's BP (*) | (*) if framepointer_enabled && varp < sp
// +------------------+ <- frame->varp
// | locals |
// +------------------+
// | args to callee |
// +------------------+ <- frame->sp
//
// (arm)
// +------------------+
// | args from caller |
// +------------------+ <- frame->argp
// | caller's retaddr |
// +------------------+ <- frame->varp
// | locals |
// +------------------+
// | args to callee |
// +------------------+
// | return address |
// +------------------+ <- frame->sp
type adjustinfo struct {
old stack
delta uintptr // ptr distance from old to new stack (newbase - oldbase)
}
// Adjustpointer checks whether *vpp is in the old stack described by adjinfo.
// If so, it rewrites *vpp to point into the new stack.
func adjustpointer(adjinfo *adjustinfo, vpp unsafe.Pointer) {
pp := (*unsafe.Pointer)(vpp)
p := *pp
if stackDebug >= 4 {
print(" ", pp, ":", p, "\n")
}
if adjinfo.old.lo <= uintptr(p) && uintptr(p) < adjinfo.old.hi {
*pp = add(p, adjinfo.delta)
if stackDebug >= 3 {
print(" adjust ptr ", pp, ":", p, " -> ", *pp, "\n")
}
}
}
type gobitvector struct {
n uintptr
bytedata []uint8
}
func gobv(bv bitvector) gobitvector {
return gobitvector{
uintptr(bv.n),
(*[1 << 30]byte)(unsafe.Pointer(bv.bytedata))[:(bv.n+7)/8],
}
}
func ptrbits(bv *gobitvector, i uintptr) uint8 {
return (bv.bytedata[i/4] >> ((i & 3) * 2)) & 3
}
// bv describes the memory starting at address scanp.
// Adjust any pointers contained therein.
func adjustpointers(scanp unsafe.Pointer, cbv *bitvector, adjinfo *adjustinfo, f *_func) {
bv := gobv(*cbv)
minp := adjinfo.old.lo
maxp := adjinfo.old.hi
delta := adjinfo.delta
num := uintptr(bv.n) / typeBitsWidth
for i := uintptr(0); i < num; i++ {
if stackDebug >= 4 {
print(" ", add(scanp, i*ptrSize), ":", mapnames[ptrbits(&bv, i)], ":", hex(*(*uintptr)(add(scanp, i*ptrSize))), " # ", i, " ", bv.bytedata[i/4], "\n")
}
switch ptrbits(&bv, i) {
default:
throw("unexpected pointer bits")
case typeDead:
if debug.gcdead != 0 {
*(*unsafe.Pointer)(add(scanp, i*ptrSize)) = unsafe.Pointer(uintptr(poisonStack))
}
case typeScalar:
// ok
case typePointer:
p := *(*unsafe.Pointer)(add(scanp, i*ptrSize))
up := uintptr(p)
if f != nil && 0 < up && up < _PageSize && debug.invalidptr != 0 || up == poisonStack {
// Looks like a junk value in a pointer slot.
// Live analysis wrong?
getg().m.traceback = 2
print("runtime: bad pointer in frame ", funcname(f), " at ", add(scanp, i*ptrSize), ": ", p, "\n")
throw("invalid stack pointer")
}
if minp <= up && up < maxp {
if stackDebug >= 3 {
print("adjust ptr ", p, " ", funcname(f), "\n")
}
*(*unsafe.Pointer)(add(scanp, i*ptrSize)) = unsafe.Pointer(up + delta)
}
}
}
}
// Note: the argument/return area is adjusted by the callee.
func adjustframe(frame *stkframe, arg unsafe.Pointer) bool {
adjinfo := (*adjustinfo)(arg)
targetpc := frame.continpc
if targetpc == 0 {
// Frame is dead.
return true
}
f := frame.fn
if stackDebug >= 2 {
print(" adjusting ", funcname(f), " frame=[", hex(frame.sp), ",", hex(frame.fp), "] pc=", hex(frame.pc), " continpc=", hex(frame.continpc), "\n")
}
if f.entry == systemstack_switchPC {
// A special routine at the bottom of stack of a goroutine that does an systemstack call.
// We will allow it to be copied even though we don't
// have full GC info for it (because it is written in asm).
return true
}
if targetpc != f.entry {
targetpc--
}
pcdata := pcdatavalue(f, _PCDATA_StackMapIndex, targetpc)
if pcdata == -1 {
pcdata = 0 // in prologue
}
// Adjust local variables if stack frame has been allocated.
size := frame.varp - frame.sp
var minsize uintptr
switch thechar {
case '6', '8':
minsize = 0
case '7':
minsize = spAlign
default:
minsize = ptrSize
}
if size > minsize {
var bv bitvector
stackmap := (*stackmap)(funcdata(f, _FUNCDATA_LocalsPointerMaps))
if stackmap == nil || stackmap.n <= 0 {
print("runtime: frame ", funcname(f), " untyped locals ", hex(frame.varp-size), "+", hex(size), "\n")
throw("missing stackmap")
}
// Locals bitmap information, scan just the pointers in locals.
if pcdata < 0 || pcdata >= stackmap.n {
// don't know where we are
print("runtime: pcdata is ", pcdata, " and ", stackmap.n, " locals stack map entries for ", funcname(f), " (targetpc=", targetpc, ")\n")
throw("bad symbol table")
}
bv = stackmapdata(stackmap, pcdata)
size = (uintptr(bv.n) / typeBitsWidth) * ptrSize
if stackDebug >= 3 {
print(" locals ", pcdata, "/", stackmap.n, " ", size/ptrSize, " words ", bv.bytedata, "\n")
}
adjustpointers(unsafe.Pointer(frame.varp-size), &bv, adjinfo, f)
}
// Adjust saved base pointer if there is one.
if thechar == '6' && frame.argp-frame.varp == 2*regSize {
if !framepointer_enabled {
print("runtime: found space for saved base pointer, but no framepointer experiment\n")
print("argp=", hex(frame.argp), " varp=", hex(frame.varp), "\n")
throw("bad frame layout")
}
if stackDebug >= 3 {
print(" saved bp\n")
}
adjustpointer(adjinfo, unsafe.Pointer(frame.varp))
}
// Adjust arguments.
if frame.arglen > 0 {
var bv bitvector
if frame.argmap != nil {
bv = *frame.argmap
} else {
stackmap := (*stackmap)(funcdata(f, _FUNCDATA_ArgsPointerMaps))
if stackmap == nil || stackmap.n <= 0 {
print("runtime: frame ", funcname(f), " untyped args ", frame.argp, "+", uintptr(frame.arglen), "\n")
throw("missing stackmap")
}
if pcdata < 0 || pcdata >= stackmap.n {
// don't know where we are
print("runtime: pcdata is ", pcdata, " and ", stackmap.n, " args stack map entries for ", funcname(f), " (targetpc=", targetpc, ")\n")
throw("bad symbol table")
}
bv = stackmapdata(stackmap, pcdata)
}
if stackDebug >= 3 {
print(" args\n")
}
adjustpointers(unsafe.Pointer(frame.argp), &bv, adjinfo, nil)
}
return true
}
func adjustctxt(gp *g, adjinfo *adjustinfo) {
adjustpointer(adjinfo, (unsafe.Pointer)(&gp.sched.ctxt))
}
func adjustdefers(gp *g, adjinfo *adjustinfo) {
// Adjust defer argument blocks the same way we adjust active stack frames.
tracebackdefers(gp, adjustframe, noescape(unsafe.Pointer(adjinfo)))
// Adjust pointers in the Defer structs.
// Defer structs themselves are never on the stack.
for d := gp._defer; d != nil; d = d.link {
adjustpointer(adjinfo, (unsafe.Pointer)(&d.fn))
adjustpointer(adjinfo, (unsafe.Pointer)(&d.sp))
adjustpointer(adjinfo, (unsafe.Pointer)(&d._panic))
}
}
func adjustpanics(gp *g, adjinfo *adjustinfo) {
// Panics are on stack and already adjusted.
// Update pointer to head of list in G.
adjustpointer(adjinfo, (unsafe.Pointer)(&gp._panic))
}
func adjustsudogs(gp *g, adjinfo *adjustinfo) {
// the data elements pointed to by a SudoG structure
// might be in the stack.
for s := gp.waiting; s != nil; s = s.waitlink {
adjustpointer(adjinfo, (unsafe.Pointer)(&s.elem))
adjustpointer(adjinfo, (unsafe.Pointer)(&s.selectdone))
}
}
func fillstack(stk stack, b byte) {
for p := stk.lo; p < stk.hi; p++ {
*(*byte)(unsafe.Pointer(p)) = b
}
}
// Copies gp's stack to a new stack of a different size.
// Caller must have changed gp status to Gcopystack.
func copystack(gp *g, newsize uintptr) {
if gp.syscallsp != 0 {
throw("stack growth not allowed in system call")
}
old := gp.stack
if old.lo == 0 {
throw("nil stackbase")
}
used := old.hi - gp.sched.sp
// allocate new stack
new := stackalloc(uint32(newsize))
if stackPoisonCopy != 0 {
fillstack(new, 0xfd)
}
if stackDebug >= 1 {
print("copystack gp=", gp, " [", hex(old.lo), " ", hex(old.hi-used), " ", hex(old.hi), "]/", old.hi-old.lo, " -> [", hex(new.lo), " ", hex(new.hi-used), " ", hex(new.hi), "]/", newsize, "\n")
}
// adjust pointers in the to-be-copied frames
var adjinfo adjustinfo
adjinfo.old = old
adjinfo.delta = new.hi - old.hi
gentraceback(^uintptr(0), ^uintptr(0), 0, gp, 0, nil, 0x7fffffff, adjustframe, noescape(unsafe.Pointer(&adjinfo)), 0)
// adjust other miscellaneous things that have pointers into stacks.
adjustctxt(gp, &adjinfo)
adjustdefers(gp, &adjinfo)
adjustpanics(gp, &adjinfo)
adjustsudogs(gp, &adjinfo)
// copy the stack to the new location
if stackPoisonCopy != 0 {
fillstack(new, 0xfb)
}
memmove(unsafe.Pointer(new.hi-used), unsafe.Pointer(old.hi-used), used)
// Swap out old stack for new one
gp.stack = new
gp.stackguard0 = new.lo + _StackGuard // NOTE: might clobber a preempt request
gp.sched.sp = new.hi - used
// free old stack
if stackPoisonCopy != 0 {
fillstack(old, 0xfc)
}
if newsize > old.hi-old.lo {
// growing, free stack immediately
stackfree(old)
} else {
// shrinking, queue up free operation. We can't actually free the stack
// just yet because we might run into the following situation:
// 1) GC starts, scans a SudoG but does not yet mark the SudoG.elem pointer
// 2) The stack that pointer points to is shrunk
// 3) The old stack is freed
// 4) The containing span is marked free
// 5) GC attempts to mark the SudoG.elem pointer. The marking fails because
// the pointer looks like a pointer into a free span.
// By not freeing, we prevent step #4 until GC is done.
lock(&stackpoolmu)
*(*stack)(unsafe.Pointer(old.lo)) = stackfreequeue
stackfreequeue = old
unlock(&stackpoolmu)
}
}
// round x up to a power of 2.
func round2(x int32) int32 {
s := uint(0)
for 1<<s < x {
s++
}
return 1 << s
}
// Called from runtime·morestack when more stack is needed.
// Allocate larger stack and relocate to new stack.
// Stack growth is multiplicative, for constant amortized cost.
//
// g->atomicstatus will be Grunning or Gscanrunning upon entry.
// If the GC is trying to stop this g then it will set preemptscan to true.
func newstack() {
thisg := getg()
// TODO: double check all gp. shouldn't be getg().
if thisg.m.morebuf.g.ptr().stackguard0 == stackFork {
throw("stack growth after fork")
}
if thisg.m.morebuf.g.ptr() != thisg.m.curg {
print("runtime: newstack called from g=", thisg.m.morebuf.g, "\n"+"\tm=", thisg.m, " m->curg=", thisg.m.curg, " m->g0=", thisg.m.g0, " m->gsignal=", thisg.m.gsignal, "\n")
morebuf := thisg.m.morebuf
traceback(morebuf.pc, morebuf.sp, morebuf.lr, morebuf.g.ptr())
throw("runtime: wrong goroutine in newstack")
}
if thisg.m.curg.throwsplit {
gp := thisg.m.curg
// Update syscallsp, syscallpc in case traceback uses them.
morebuf := thisg.m.morebuf
gp.syscallsp = morebuf.sp
gp.syscallpc = morebuf.pc
print("runtime: newstack sp=", hex(gp.sched.sp), " stack=[", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n",
"\tmorebuf={pc:", hex(morebuf.pc), " sp:", hex(morebuf.sp), " lr:", hex(morebuf.lr), "}\n",
"\tsched={pc:", hex(gp.sched.pc), " sp:", hex(gp.sched.sp), " lr:", hex(gp.sched.lr), " ctxt:", gp.sched.ctxt, "}\n")
traceback(morebuf.pc, morebuf.sp, morebuf.lr, gp)
throw("runtime: stack split at bad time")
}
gp := thisg.m.curg
morebuf := thisg.m.morebuf
thisg.m.morebuf.pc = 0
thisg.m.morebuf.lr = 0
thisg.m.morebuf.sp = 0
thisg.m.morebuf.g = 0
rewindmorestack(&gp.sched)
// NOTE: stackguard0 may change underfoot, if another thread
// is about to try to preempt gp. Read it just once and use that same
// value now and below.
preempt := atomicloaduintptr(&gp.stackguard0) == stackPreempt
// Be conservative about where we preempt.
// We are interested in preempting user Go code, not runtime code.
// If we're holding locks, mallocing, or preemption is disabled, don't
// preempt.
// This check is very early in newstack so that even the status change
// from Grunning to Gwaiting and back doesn't happen in this case.
// That status change by itself can be viewed as a small preemption,
// because the GC might change Gwaiting to Gscanwaiting, and then
// this goroutine has to wait for the GC to finish before continuing.
// If the GC is in some way dependent on this goroutine (for example,
// it needs a lock held by the goroutine), that small preemption turns
// into a real deadlock.
if preempt {
if thisg.m.locks != 0 || thisg.m.mallocing != 0 || thisg.m.preemptoff != "" || thisg.m.p.status != _Prunning {
// Let the goroutine keep running for now.
// gp->preempt is set, so it will be preempted next time.
gp.stackguard0 = gp.stack.lo + _StackGuard
gogo(&gp.sched) // never return
}
}
// The goroutine must be executing in order to call newstack,
// so it must be Grunning (or Gscanrunning).
casgstatus(gp, _Grunning, _Gwaiting)
gp.waitreason = "stack growth"
if gp.stack.lo == 0 {
throw("missing stack in newstack")
}
sp := gp.sched.sp
if thechar == '6' || thechar == '8' {
// The call to morestack cost a word.
sp -= ptrSize
}
if stackDebug >= 1 || sp < gp.stack.lo {
print("runtime: newstack sp=", hex(sp), " stack=[", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n",
"\tmorebuf={pc:", hex(morebuf.pc), " sp:", hex(morebuf.sp), " lr:", hex(morebuf.lr), "}\n",
"\tsched={pc:", hex(gp.sched.pc), " sp:", hex(gp.sched.sp), " lr:", hex(gp.sched.lr), " ctxt:", gp.sched.ctxt, "}\n")
}
if sp < gp.stack.lo {
print("runtime: gp=", gp, ", gp->status=", hex(readgstatus(gp)), "\n ")
print("runtime: split stack overflow: ", hex(sp), " < ", hex(gp.stack.lo), "\n")
throw("runtime: split stack overflow")
}
if gp.sched.ctxt != nil {
// morestack wrote sched.ctxt on its way in here,
// without a write barrier. Run the write barrier now.
// It is not possible to be preempted between then
// and now, so it's okay.
writebarrierptr_nostore((*uintptr)(unsafe.Pointer(&gp.sched.ctxt)), uintptr(gp.sched.ctxt))
}
if preempt {
if gp == thisg.m.g0 {
throw("runtime: preempt g0")
}
if thisg.m.p == nil && thisg.m.locks == 0 {
throw("runtime: g is running but p is not")
}
if gp.preemptscan {
for !castogscanstatus(gp, _Gwaiting, _Gscanwaiting) {
// Likely to be racing with the GC as it sees a _Gwaiting and does the stack scan.
// If so this stack will be scanned twice which does not change correctness.
}
gcphasework(gp)
casfrom_Gscanstatus(gp, _Gscanwaiting, _Gwaiting)
casgstatus(gp, _Gwaiting, _Grunning)
gp.stackguard0 = gp.stack.lo + _StackGuard
gp.preempt = false
gp.preemptscan = false // Tells the GC premption was successful.
gogo(&gp.sched) // never return
}
// Act like goroutine called runtime.Gosched.
casgstatus(gp, _Gwaiting, _Grunning)
gopreempt_m(gp) // never return
}
// Allocate a bigger segment and move the stack.
oldsize := int(gp.stack.hi - gp.stack.lo)
newsize := oldsize * 2
if uintptr(newsize) > maxstacksize {
print("runtime: goroutine stack exceeds ", maxstacksize, "-byte limit\n")
throw("stack overflow")
}
casgstatus(gp, _Gwaiting, _Gcopystack)
// The concurrent GC will not scan the stack while we are doing the copy since
// the gp is in a Gcopystack status.
copystack(gp, uintptr(newsize))
if stackDebug >= 1 {
print("stack grow done\n")
}
casgstatus(gp, _Gcopystack, _Grunning)
gogo(&gp.sched)
}
//go:nosplit
func nilfunc() {
*(*uint8)(nil) = 0
}
// adjust Gobuf as if it executed a call to fn
// and then did an immediate gosave.
func gostartcallfn(gobuf *gobuf, fv *funcval) {
var fn unsafe.Pointer
if fv != nil {
fn = (unsafe.Pointer)(fv.fn)
} else {
fn = unsafe.Pointer(funcPC(nilfunc))
}
gostartcall(gobuf, fn, (unsafe.Pointer)(fv))
}
// Maybe shrink the stack being used by gp.
// Called at garbage collection time.
func shrinkstack(gp *g) {
if readgstatus(gp) == _Gdead {
if gp.stack.lo != 0 {
// Free whole stack - it will get reallocated
// if G is used again.
stackfree(gp.stack)
gp.stack.lo = 0
gp.stack.hi = 0
}
return
}
if gp.stack.lo == 0 {
throw("missing stack in shrinkstack")
}
oldsize := gp.stack.hi - gp.stack.lo
newsize := oldsize / 2
if newsize < _FixedStack {
return // don't shrink below the minimum-sized stack
}
used := gp.stack.hi - gp.sched.sp
if used >= oldsize/4 {
return // still using at least 1/4 of the segment.
}
// We can't copy the stack if we're in a syscall.
// The syscall might have pointers into the stack.
if gp.syscallsp != 0 {
return
}
if goos_windows != 0 && gp.m != nil && gp.m.libcallsp != 0 {
return
}
if stackDebug > 0 {
print("shrinking stack ", oldsize, "->", newsize, "\n")
}
oldstatus := casgcopystack(gp)
copystack(gp, newsize)
casgstatus(gp, _Gcopystack, oldstatus)
}
// Do any delayed stack freeing that was queued up during GC.
func shrinkfinish() {
lock(&stackpoolmu)
s := stackfreequeue
stackfreequeue = stack{}
unlock(&stackpoolmu)
for s.lo != 0 {
t := *(*stack)(unsafe.Pointer(s.lo))
stackfree(s)
s = t
}
}
//go:nosplit
func morestackc() {
systemstack(func() {
throw("attempt to execute C code on Go stack")
})
}