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Diffstat (limited to 'src/runtime/stack.go')
| -rw-r--r-- | src/runtime/stack.go | 1335 |
1 files changed, 1335 insertions, 0 deletions
diff --git a/src/runtime/stack.go b/src/runtime/stack.go new file mode 100644 index 0000000..7b9dce5 --- /dev/null +++ b/src/runtime/stack.go @@ -0,0 +1,1335 @@ +// 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 ( + "internal/cpu" + "runtime/internal/atomic" + "runtime/internal/sys" + "unsafe" +) + +/* +Stack layout parameters. +Included both by runtime (compiled via 6c) and linkers (compiled via gcc). + +The per-goroutine g->stackguard is set to point StackGuard bytes +above the bottom of the stack. Each function compares its stack +pointer against g->stackguard to check for overflow. To cut one +instruction from the check sequence for functions with tiny frames, +the stack is allowed to protrude StackSmall bytes below the stack +guard. Functions with large frames don't bother with the check and +always call morestack. The sequences are (for amd64, others are +similar): + + guard = g->stackguard + frame = function's stack frame size + argsize = size of function arguments (call + return) + + stack frame size <= StackSmall: + CMPQ guard, SP + JHI 3(PC) + MOVQ m->morearg, $(argsize << 32) + CALL morestack(SB) + + stack frame size > StackSmall but < StackBig + LEAQ (frame-StackSmall)(SP), R0 + CMPQ guard, R0 + JHI 3(PC) + MOVQ m->morearg, $(argsize << 32) + CALL morestack(SB) + + stack frame size >= StackBig: + MOVQ m->morearg, $((argsize << 32) | frame) + CALL morestack(SB) + +The bottom StackGuard - StackSmall bytes are important: there has +to be enough room to execute functions that refuse to check for +stack overflow, either because they need to be adjacent to the +actual caller's frame (deferproc) or because they handle the imminent +stack overflow (morestack). + +For example, deferproc might call malloc, which does one of the +above checks (without allocating a full frame), which might trigger +a call to morestack. This sequence needs to fit in the bottom +section of the stack. On amd64, morestack's frame is 40 bytes, and +deferproc's frame is 56 bytes. That fits well within the +StackGuard - StackSmall bytes at the bottom. +The linkers explore all possible call traces involving non-splitting +functions to make sure that this limit cannot be violated. +*/ + +const ( + // StackSystem is a number of additional bytes to add + // to each stack below the usual guard area for OS-specific + // purposes like signal handling. Used on Windows, Plan 9, + // and iOS because they do not use a separate stack. + _StackSystem = sys.GoosWindows*512*sys.PtrSize + sys.GoosPlan9*512 + sys.GoosIos*sys.GoarchArm64*1024 + + // The minimum size of stack used by Go code + _StackMin = 2048 + + // The minimum stack size to allocate. + // The hackery here rounds FixedStack0 up to a power of 2. + _FixedStack0 = _StackMin + _StackSystem + _FixedStack1 = _FixedStack0 - 1 + _FixedStack2 = _FixedStack1 | (_FixedStack1 >> 1) + _FixedStack3 = _FixedStack2 | (_FixedStack2 >> 2) + _FixedStack4 = _FixedStack3 | (_FixedStack3 >> 4) + _FixedStack5 = _FixedStack4 | (_FixedStack4 >> 8) + _FixedStack6 = _FixedStack5 | (_FixedStack5 >> 16) + _FixedStack = _FixedStack6 + 1 + + // Functions that need frames bigger than this use an extra + // instruction to do the stack split check, to avoid overflow + // in case SP - framesize wraps below zero. + // This value can be no bigger than the size of the unmapped + // space at zero. + _StackBig = 4096 + + // The stack guard is a pointer this many bytes above the + // bottom of the stack. + _StackGuard = 928*sys.StackGuardMultiplier + _StackSystem + + // After a stack split check the SP is allowed to be this + // many bytes below the stack guard. This saves an instruction + // in the checking sequence for tiny frames. + _StackSmall = 128 + + // The maximum number of bytes that a chain of NOSPLIT + // functions can use. + _StackLimit = _StackGuard - _StackSystem - _StackSmall +) + +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 + stackNoCache = 0 // disable per-P small stack caches + + // check the BP links during traceback. + debugCheckBP = false +) + +const ( + uintptrMask = 1<<(8*sys.PtrSize) - 1 + + // 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. +var stackpool [_NumStackOrders]struct { + item stackpoolItem + _ [cpu.CacheLinePadSize - unsafe.Sizeof(stackpoolItem{})%cpu.CacheLinePadSize]byte +} + +//go:notinheap +type stackpoolItem struct { + mu mutex + span mSpanList +} + +// Global pool of large stack spans. +var stackLarge struct { + lock mutex + free [heapAddrBits - pageShift]mSpanList // free lists by log_2(s.npages) +} + +func stackinit() { + if _StackCacheSize&_PageMask != 0 { + throw("cache size must be a multiple of page size") + } + for i := range stackpool { + stackpool[i].item.span.init() + lockInit(&stackpool[i].item.mu, lockRankStackpool) + } + for i := range stackLarge.free { + stackLarge.free[i].init() + lockInit(&stackLarge.lock, lockRankStackLarge) + } +} + +// stacklog2 returns ⌊log_2(n)⌋. +func stacklog2(n uintptr) int { + log2 := 0 + for n > 1 { + n >>= 1 + log2++ + } + return log2 +} + +// Allocates a stack from the free pool. Must be called with +// stackpool[order].item.mu held. +func stackpoolalloc(order uint8) gclinkptr { + list := &stackpool[order].item.span + s := list.first + lockWithRankMayAcquire(&mheap_.lock, lockRankMheap) + if s == nil { + // no free stacks. Allocate another span worth. + s = mheap_.allocManual(_StackCacheSize>>_PageShift, spanAllocStack) + if s == nil { + throw("out of memory") + } + if s.allocCount != 0 { + throw("bad allocCount") + } + if s.manualFreeList.ptr() != nil { + throw("bad manualFreeList") + } + osStackAlloc(s) + s.elemsize = _FixedStack << order + for i := uintptr(0); i < _StackCacheSize; i += s.elemsize { + x := gclinkptr(s.base() + i) + x.ptr().next = s.manualFreeList + s.manualFreeList = x + } + list.insert(s) + } + x := s.manualFreeList + if x.ptr() == nil { + throw("span has no free stacks") + } + s.manualFreeList = x.ptr().next + s.allocCount++ + if s.manualFreeList.ptr() == nil { + // all stacks in s are allocated. + list.remove(s) + } + return x +} + +// Adds stack x to the free pool. Must be called with stackpool[order].item.mu held. +func stackpoolfree(x gclinkptr, order uint8) { + s := spanOfUnchecked(uintptr(x)) + if s.state.get() != mSpanManual { + throw("freeing stack not in a stack span") + } + if s.manualFreeList.ptr() == nil { + // s will now have a free stack + stackpool[order].item.span.insert(s) + } + x.ptr().next = s.manualFreeList + s.manualFreeList = x + s.allocCount-- + if gcphase == _GCoff && s.allocCount == 0 { + // Span is completely free. Return it to the heap + // immediately if we're sweeping. + // + // If GC is active, we delay the free until the end of + // GC to avoid the following type of situation: + // + // 1) GC starts, scans a SudoG but does not yet mark the SudoG.elem pointer + // 2) The stack that pointer points to is copied + // 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. + stackpool[order].item.span.remove(s) + s.manualFreeList = 0 + osStackFree(s) + mheap_.freeManual(s, spanAllocStack) + } +} + +// stackcacherefill/stackcacherelease implement a global pool of stack segments. +// The pool is required to prevent unlimited growth of per-thread caches. +// +//go:systemstack +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(&stackpool[order].item.mu) + for size < _StackCacheSize/2 { + x := stackpoolalloc(order) + x.ptr().next = list + list = x + size += _FixedStack << order + } + unlock(&stackpool[order].item.mu) + c.stackcache[order].list = list + c.stackcache[order].size = size +} + +//go:systemstack +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(&stackpool[order].item.mu) + for size > _StackCacheSize/2 { + y := x.ptr().next + stackpoolfree(x, order) + x = y + size -= _FixedStack << order + } + unlock(&stackpool[order].item.mu) + c.stackcache[order].list = x + c.stackcache[order].size = size +} + +//go:systemstack +func stackcache_clear(c *mcache) { + if stackDebug >= 1 { + print("stackcache clear\n") + } + for order := uint8(0); order < _NumStackOrders; order++ { + lock(&stackpool[order].item.mu) + 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(&stackpool[order].item.mu) + } +} + +// stackalloc allocates an n byte stack. +// +// stackalloc must run on the system stack because it uses per-P +// resources and must not split the stack. +// +//go:systemstack +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 { + n = uint32(alignUp(uintptr(n), physPageSize)) + v := sysAlloc(uintptr(n), &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 n < _FixedStack<<_NumStackOrders && n < _StackCacheSize { + order := uint8(0) + n2 := n + for n2 > _FixedStack { + order++ + n2 >>= 1 + } + var x gclinkptr + if stackNoCache != 0 || thisg.m.p == 0 || thisg.m.preemptoff != "" { + // thisg.m.p == 0 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(&stackpool[order].item.mu) + x = stackpoolalloc(order) + unlock(&stackpool[order].item.mu) + } else { + c := thisg.m.p.ptr().mcache + 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 { + var s *mspan + npage := uintptr(n) >> _PageShift + log2npage := stacklog2(npage) + + // Try to get a stack from the large stack cache. + lock(&stackLarge.lock) + if !stackLarge.free[log2npage].isEmpty() { + s = stackLarge.free[log2npage].first + stackLarge.free[log2npage].remove(s) + } + unlock(&stackLarge.lock) + + lockWithRankMayAcquire(&mheap_.lock, lockRankMheap) + + if s == nil { + // Allocate a new stack from the heap. + s = mheap_.allocManual(npage, spanAllocStack) + if s == nil { + throw("out of memory") + } + osStackAlloc(s) + s.elemsize = uintptr(n) + } + v = unsafe.Pointer(s.base()) + } + + if raceenabled { + racemalloc(v, uintptr(n)) + } + if msanenabled { + msanmalloc(v, uintptr(n)) + } + if stackDebug >= 1 { + print(" allocated ", v, "\n") + } + return stack{uintptr(v), uintptr(v) + uintptr(n)} +} + +// stackfree frees an n byte stack allocation at stk. +// +// stackfree must run on the system stack because it uses per-P +// resources and must not split the stack. +// +//go:systemstack +func stackfree(stk stack) { + gp := getg() + v := unsafe.Pointer(stk.lo) + n := stk.hi - stk.lo + if n&(n-1) != 0 { + throw("stack not a power of 2") + } + if stk.lo+n < stk.hi { + throw("bad stack size") + } + if stackDebug >= 1 { + println("stackfree", v, n) + memclrNoHeapPointers(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 msanenabled { + msanfree(v, n) + } + if n < _FixedStack<<_NumStackOrders && n < _StackCacheSize { + order := uint8(0) + n2 := n + for n2 > _FixedStack { + order++ + n2 >>= 1 + } + x := gclinkptr(v) + if stackNoCache != 0 || gp.m.p == 0 || gp.m.preemptoff != "" { + lock(&stackpool[order].item.mu) + stackpoolfree(x, order) + unlock(&stackpool[order].item.mu) + } else { + c := gp.m.p.ptr().mcache + 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 := spanOfUnchecked(uintptr(v)) + if s.state.get() != mSpanManual { + println(hex(s.base()), v) + throw("bad span state") + } + if gcphase == _GCoff { + // Free the stack immediately if we're + // sweeping. + osStackFree(s) + mheap_.freeManual(s, spanAllocStack) + } else { + // If the GC is running, we can't return a + // stack span to the heap because it could be + // reused as a heap span, and this state + // change would race with GC. Add it to the + // large stack cache instead. + log2npage := stacklog2(s.npages) + lock(&stackLarge.lock) + stackLarge.free[log2npage].insert(s) + unlock(&stackLarge.lock) + } + } +} + +var maxstacksize uintptr = 1 << 20 // enough until runtime.main sets it for real + +var maxstackceiling = maxstacksize + +var ptrnames = []string{ + 0: "scalar", + 1: "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) + cache pcvalueCache + + // sghi is the highest sudog.elem on the stack. + sghi uintptr +} + +// 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 := (*uintptr)(vpp) + p := *pp + if stackDebug >= 4 { + print(" ", pp, ":", hex(p), "\n") + } + if adjinfo.old.lo <= p && p < adjinfo.old.hi { + *pp = p + adjinfo.delta + if stackDebug >= 3 { + print(" adjust ptr ", pp, ":", hex(p), " -> ", hex(*pp), "\n") + } + } +} + +// Information from the compiler about the layout of stack frames. +// Note: this type must agree with reflect.bitVector. +type bitvector struct { + n int32 // # of bits + bytedata *uint8 +} + +// ptrbit returns the i'th bit in bv. +// ptrbit is less efficient than iterating directly over bitvector bits, +// and should only be used in non-performance-critical code. +// See adjustpointers for an example of a high-efficiency walk of a bitvector. +func (bv *bitvector) ptrbit(i uintptr) uint8 { + b := *(addb(bv.bytedata, i/8)) + return (b >> (i % 8)) & 1 +} + +// bv describes the memory starting at address scanp. +// Adjust any pointers contained therein. +func adjustpointers(scanp unsafe.Pointer, bv *bitvector, adjinfo *adjustinfo, f funcInfo) { + minp := adjinfo.old.lo + maxp := adjinfo.old.hi + delta := adjinfo.delta + num := uintptr(bv.n) + // If this frame might contain channel receive slots, use CAS + // to adjust pointers. If the slot hasn't been received into + // yet, it may contain stack pointers and a concurrent send + // could race with adjusting those pointers. (The sent value + // itself can never contain stack pointers.) + useCAS := uintptr(scanp) < adjinfo.sghi + for i := uintptr(0); i < num; i += 8 { + if stackDebug >= 4 { + for j := uintptr(0); j < 8; j++ { + print(" ", add(scanp, (i+j)*sys.PtrSize), ":", ptrnames[bv.ptrbit(i+j)], ":", hex(*(*uintptr)(add(scanp, (i+j)*sys.PtrSize))), " # ", i, " ", *addb(bv.bytedata, i/8), "\n") + } + } + b := *(addb(bv.bytedata, i/8)) + for b != 0 { + j := uintptr(sys.Ctz8(b)) + b &= b - 1 + pp := (*uintptr)(add(scanp, (i+j)*sys.PtrSize)) + retry: + p := *pp + if f.valid() && 0 < p && p < minLegalPointer && debug.invalidptr != 0 { + // 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 ", pp, ": ", hex(p), "\n") + throw("invalid pointer found on stack") + } + if minp <= p && p < maxp { + if stackDebug >= 3 { + print("adjust ptr ", hex(p), " ", funcname(f), "\n") + } + if useCAS { + ppu := (*unsafe.Pointer)(unsafe.Pointer(pp)) + if !atomic.Casp1(ppu, unsafe.Pointer(p), unsafe.Pointer(p+delta)) { + goto retry + } + } else { + *pp = p + delta + } + } + } + } +} + +// Note: the argument/return area is adjusted by the callee. +func adjustframe(frame *stkframe, arg unsafe.Pointer) bool { + adjinfo := (*adjustinfo)(arg) + if frame.continpc == 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.funcID == funcID_systemstack_switch { + // A special routine at the bottom of stack of a goroutine that does a 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 + } + + locals, args, objs := getStackMap(frame, &adjinfo.cache, true) + + // Adjust local variables if stack frame has been allocated. + if locals.n > 0 { + size := uintptr(locals.n) * sys.PtrSize + adjustpointers(unsafe.Pointer(frame.varp-size), &locals, adjinfo, f) + } + + // Adjust saved base pointer if there is one. + // TODO what about arm64 frame pointer adjustment? + if sys.ArchFamily == sys.AMD64 && frame.argp-frame.varp == 2*sys.RegSize { + if stackDebug >= 3 { + print(" saved bp\n") + } + if debugCheckBP { + // Frame pointers should always point to the next higher frame on + // the Go stack (or be nil, for the top frame on the stack). + bp := *(*uintptr)(unsafe.Pointer(frame.varp)) + if bp != 0 && (bp < adjinfo.old.lo || bp >= adjinfo.old.hi) { + println("runtime: found invalid frame pointer") + print("bp=", hex(bp), " min=", hex(adjinfo.old.lo), " max=", hex(adjinfo.old.hi), "\n") + throw("bad frame pointer") + } + } + adjustpointer(adjinfo, unsafe.Pointer(frame.varp)) + } + + // Adjust arguments. + if args.n > 0 { + if stackDebug >= 3 { + print(" args\n") + } + adjustpointers(unsafe.Pointer(frame.argp), &args, adjinfo, funcInfo{}) + } + + // Adjust pointers in all stack objects (whether they are live or not). + // See comments in mgcmark.go:scanframeworker. + if frame.varp != 0 { + for _, obj := range objs { + off := obj.off + base := frame.varp // locals base pointer + if off >= 0 { + base = frame.argp // arguments and return values base pointer + } + p := base + uintptr(off) + if p < frame.sp { + // Object hasn't been allocated in the frame yet. + // (Happens when the stack bounds check fails and + // we call into morestack.) + continue + } + t := obj.typ + gcdata := t.gcdata + var s *mspan + if t.kind&kindGCProg != 0 { + // See comments in mgcmark.go:scanstack + s = materializeGCProg(t.ptrdata, gcdata) + gcdata = (*byte)(unsafe.Pointer(s.startAddr)) + } + for i := uintptr(0); i < t.ptrdata; i += sys.PtrSize { + if *addb(gcdata, i/(8*sys.PtrSize))>>(i/sys.PtrSize&7)&1 != 0 { + adjustpointer(adjinfo, unsafe.Pointer(p+i)) + } + } + if s != nil { + dematerializeGCProg(s) + } + } + } + + return true +} + +func adjustctxt(gp *g, adjinfo *adjustinfo) { + adjustpointer(adjinfo, unsafe.Pointer(&gp.sched.ctxt)) + if !framepointer_enabled { + return + } + if debugCheckBP { + bp := gp.sched.bp + if bp != 0 && (bp < adjinfo.old.lo || bp >= adjinfo.old.hi) { + println("runtime: found invalid top frame pointer") + print("bp=", hex(bp), " min=", hex(adjinfo.old.lo), " max=", hex(adjinfo.old.hi), "\n") + throw("bad top frame pointer") + } + } + adjustpointer(adjinfo, unsafe.Pointer(&gp.sched.bp)) +} + +func adjustdefers(gp *g, adjinfo *adjustinfo) { + // Adjust pointers in the Defer structs. + // We need to do this first because we need to adjust the + // defer.link fields so we always work on the new stack. + adjustpointer(adjinfo, unsafe.Pointer(&gp._defer)) + 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)) + adjustpointer(adjinfo, unsafe.Pointer(&d.link)) + adjustpointer(adjinfo, unsafe.Pointer(&d.varp)) + adjustpointer(adjinfo, unsafe.Pointer(&d.fd)) + } + + // Adjust defer argument blocks the same way we adjust active stack frames. + // Note: this code is after the loop above, so that if a defer record is + // stack allocated, we work on the copy in the new stack. + tracebackdefers(gp, adjustframe, noescape(unsafe.Pointer(adjinfo))) +} + +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)) + } +} + +func fillstack(stk stack, b byte) { + for p := stk.lo; p < stk.hi; p++ { + *(*byte)(unsafe.Pointer(p)) = b + } +} + +func findsghi(gp *g, stk stack) uintptr { + var sghi uintptr + for sg := gp.waiting; sg != nil; sg = sg.waitlink { + p := uintptr(sg.elem) + uintptr(sg.c.elemsize) + if stk.lo <= p && p < stk.hi && p > sghi { + sghi = p + } + } + return sghi +} + +// syncadjustsudogs adjusts gp's sudogs and copies the part of gp's +// stack they refer to while synchronizing with concurrent channel +// operations. It returns the number of bytes of stack copied. +func syncadjustsudogs(gp *g, used uintptr, adjinfo *adjustinfo) uintptr { + if gp.waiting == nil { + return 0 + } + + // Lock channels to prevent concurrent send/receive. + var lastc *hchan + for sg := gp.waiting; sg != nil; sg = sg.waitlink { + if sg.c != lastc { + // There is a ranking cycle here between gscan bit and + // hchan locks. Normally, we only allow acquiring hchan + // locks and then getting a gscan bit. In this case, we + // already have the gscan bit. We allow acquiring hchan + // locks here as a special case, since a deadlock can't + // happen because the G involved must already be + // suspended. So, we get a special hchan lock rank here + // that is lower than gscan, but doesn't allow acquiring + // any other locks other than hchan. + lockWithRank(&sg.c.lock, lockRankHchanLeaf) + } + lastc = sg.c + } + + // Adjust sudogs. + adjustsudogs(gp, adjinfo) + + // Copy the part of the stack the sudogs point in to + // while holding the lock to prevent races on + // send/receive slots. + var sgsize uintptr + if adjinfo.sghi != 0 { + oldBot := adjinfo.old.hi - used + newBot := oldBot + adjinfo.delta + sgsize = adjinfo.sghi - oldBot + memmove(unsafe.Pointer(newBot), unsafe.Pointer(oldBot), sgsize) + } + + // Unlock channels. + lastc = nil + for sg := gp.waiting; sg != nil; sg = sg.waitlink { + if sg.c != lastc { + unlock(&sg.c.lock) + } + lastc = sg.c + } + + return sgsize +} + +// 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), "]", " -> [", hex(new.lo), " ", hex(new.hi-used), " ", hex(new.hi), "]/", newsize, "\n") + } + + // Compute adjustment. + var adjinfo adjustinfo + adjinfo.old = old + adjinfo.delta = new.hi - old.hi + + // Adjust sudogs, synchronizing with channel ops if necessary. + ncopy := used + if !gp.activeStackChans { + if newsize < old.hi-old.lo && atomic.Load8(&gp.parkingOnChan) != 0 { + // It's not safe for someone to shrink this stack while we're actively + // parking on a channel, but it is safe to grow since we do that + // ourselves and explicitly don't want to synchronize with channels + // since we could self-deadlock. + throw("racy sudog adjustment due to parking on channel") + } + adjustsudogs(gp, &adjinfo) + } else { + // sudogs may be pointing in to the stack and gp has + // released channel locks, so other goroutines could + // be writing to gp's stack. Find the highest such + // pointer so we can handle everything there and below + // carefully. (This shouldn't be far from the bottom + // of the stack, so there's little cost in handling + // everything below it carefully.) + adjinfo.sghi = findsghi(gp, old) + + // Synchronize with channel ops and copy the part of + // the stack they may interact with. + ncopy -= syncadjustsudogs(gp, used, &adjinfo) + } + + // Copy the stack (or the rest of it) to the new location + memmove(unsafe.Pointer(new.hi-ncopy), unsafe.Pointer(old.hi-ncopy), ncopy) + + // Adjust remaining structures that have pointers into stacks. + // We have to do most of these before we traceback the new + // stack because gentraceback uses them. + adjustctxt(gp, &adjinfo) + adjustdefers(gp, &adjinfo) + adjustpanics(gp, &adjinfo) + if adjinfo.sghi != 0 { + adjinfo.sghi += adjinfo.delta + } + + // 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 + gp.stktopsp += adjinfo.delta + + // Adjust pointers in the new stack. + gentraceback(^uintptr(0), ^uintptr(0), 0, gp, 0, nil, 0x7fffffff, adjustframe, noescape(unsafe.Pointer(&adjinfo)), 0) + + // free old stack + if stackPoisonCopy != 0 { + fillstack(old, 0xfc) + } + stackfree(old) +} + +// 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 scheduler is trying to stop this g, then it will set preemptStop. +// +// This must be nowritebarrierrec because it can be called as part of +// stack growth from other nowritebarrierrec functions, but the +// compiler doesn't check this. +// +//go:nowritebarrierrec +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=", hex(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") + } + + gp := thisg.m.curg + + if thisg.m.curg.throwsplit { + // Update syscallsp, syscallpc in case traceback uses them. + morebuf := thisg.m.morebuf + gp.syscallsp = morebuf.sp + gp.syscallpc = morebuf.pc + pcname, pcoff := "(unknown)", uintptr(0) + f := findfunc(gp.sched.pc) + if f.valid() { + pcname = funcname(f) + pcoff = gp.sched.pc - f.entry + } + print("runtime: newstack at ", pcname, "+", hex(pcoff), + " 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") + + thisg.m.traceback = 2 // Include runtime frames + traceback(morebuf.pc, morebuf.sp, morebuf.lr, gp) + throw("runtime: stack split at bad time") + } + + morebuf := thisg.m.morebuf + thisg.m.morebuf.pc = 0 + thisg.m.morebuf.lr = 0 + thisg.m.morebuf.sp = 0 + thisg.m.morebuf.g = 0 + + // 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 := atomic.Loaduintptr(&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 !canPreemptM(thisg.m) { + // 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 + } + } + + if gp.stack.lo == 0 { + throw("missing stack in newstack") + } + sp := gp.sched.sp + if sys.ArchFamily == sys.AMD64 || sys.ArchFamily == sys.I386 || sys.ArchFamily == sys.WASM { + // The call to morestack cost a word. + sp -= sys.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, ", goid=", gp.goid, ", gp->status=", hex(readgstatus(gp)), "\n ") + print("runtime: split stack overflow: ", hex(sp), " < ", hex(gp.stack.lo), "\n") + throw("runtime: split stack overflow") + } + + if preempt { + if gp == thisg.m.g0 { + throw("runtime: preempt g0") + } + if thisg.m.p == 0 && thisg.m.locks == 0 { + throw("runtime: g is running but p is not") + } + + if gp.preemptShrink { + // We're at a synchronous safe point now, so + // do the pending stack shrink. + gp.preemptShrink = false + shrinkstack(gp) + } + + if gp.preemptStop { + preemptPark(gp) // never returns + } + + // Act like goroutine called runtime.Gosched. + gopreempt_m(gp) // never return + } + + // Allocate a bigger segment and move the stack. + oldsize := gp.stack.hi - gp.stack.lo + newsize := oldsize * 2 + + // Make sure we grow at least as much as needed to fit the new frame. + // (This is just an optimization - the caller of morestack will + // recheck the bounds on return.) + if f := findfunc(gp.sched.pc); f.valid() { + max := uintptr(funcMaxSPDelta(f)) + for newsize-oldsize < max+_StackGuard { + newsize *= 2 + } + } + + if newsize > maxstacksize || newsize > maxstackceiling { + if maxstacksize < maxstackceiling { + print("runtime: goroutine stack exceeds ", maxstacksize, "-byte limit\n") + } else { + print("runtime: goroutine stack exceeds ", maxstackceiling, "-byte limit\n") + } + print("runtime: sp=", hex(sp), " stack=[", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n") + throw("stack overflow") + } + + // The goroutine must be executing in order to call newstack, + // so it must be Grunning (or Gscanrunning). + casgstatus(gp, _Grunning, _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, 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)) +} + +// isShrinkStackSafe returns whether it's safe to attempt to shrink +// gp's stack. Shrinking the stack is only safe when we have precise +// pointer maps for all frames on the stack. +func isShrinkStackSafe(gp *g) bool { + // We can't copy the stack if we're in a syscall. + // The syscall might have pointers into the stack and + // often we don't have precise pointer maps for the innermost + // frames. + // + // We also can't copy the stack if we're at an asynchronous + // safe-point because we don't have precise pointer maps for + // all frames. + // + // We also can't *shrink* the stack in the window between the + // goroutine calling gopark to park on a channel and + // gp.activeStackChans being set. + return gp.syscallsp == 0 && !gp.asyncSafePoint && atomic.Load8(&gp.parkingOnChan) == 0 +} + +// Maybe shrink the stack being used by gp. +// +// gp must be stopped and we must own its stack. It may be in +// _Grunning, but only if this is our own user G. +func shrinkstack(gp *g) { + if gp.stack.lo == 0 { + throw("missing stack in shrinkstack") + } + if s := readgstatus(gp); s&_Gscan == 0 { + // We don't own the stack via _Gscan. We could still + // own it if this is our own user G and we're on the + // system stack. + if !(gp == getg().m.curg && getg() != getg().m.curg && s == _Grunning) { + // We don't own the stack. + throw("bad status in shrinkstack") + } + } + if !isShrinkStackSafe(gp) { + throw("shrinkstack at bad time") + } + // Check for self-shrinks while in a libcall. These may have + // pointers into the stack disguised as uintptrs, but these + // code paths should all be nosplit. + if gp == getg().m.curg && gp.m.libcallsp != 0 { + throw("shrinking stack in libcall") + } + + if debug.gcshrinkstackoff > 0 { + return + } + f := findfunc(gp.startpc) + if f.valid() && f.funcID == funcID_gcBgMarkWorker { + // We're not allowed to shrink the gcBgMarkWorker + // stack (see gcBgMarkWorker for explanation). + return + } + + oldsize := gp.stack.hi - gp.stack.lo + newsize := oldsize / 2 + // Don't shrink the allocation below the minimum-sized stack + // allocation. + if newsize < _FixedStack { + return + } + // Compute how much of the stack is currently in use and only + // shrink the stack if gp is using less than a quarter of its + // current stack. The currently used stack includes everything + // down to the SP plus the stack guard space that ensures + // there's room for nosplit functions. + avail := gp.stack.hi - gp.stack.lo + if used := gp.stack.hi - gp.sched.sp + _StackLimit; used >= avail/4 { + return + } + + if stackDebug > 0 { + print("shrinking stack ", oldsize, "->", newsize, "\n") + } + + copystack(gp, newsize) +} + +// freeStackSpans frees unused stack spans at the end of GC. +func freeStackSpans() { + + // Scan stack pools for empty stack spans. + for order := range stackpool { + lock(&stackpool[order].item.mu) + list := &stackpool[order].item.span + for s := list.first; s != nil; { + next := s.next + if s.allocCount == 0 { + list.remove(s) + s.manualFreeList = 0 + osStackFree(s) + mheap_.freeManual(s, spanAllocStack) + } + s = next + } + unlock(&stackpool[order].item.mu) + } + + // Free large stack spans. + lock(&stackLarge.lock) + for i := range stackLarge.free { + for s := stackLarge.free[i].first; s != nil; { + next := s.next + stackLarge.free[i].remove(s) + osStackFree(s) + mheap_.freeManual(s, spanAllocStack) + s = next + } + } + unlock(&stackLarge.lock) +} + +// getStackMap returns the locals and arguments live pointer maps, and +// stack object list for frame. +func getStackMap(frame *stkframe, cache *pcvalueCache, debug bool) (locals, args bitvector, objs []stackObjectRecord) { + targetpc := frame.continpc + if targetpc == 0 { + // Frame is dead. Return empty bitvectors. + return + } + + f := frame.fn + pcdata := int32(-1) + if targetpc != f.entry { + // Back up to the CALL. If we're at the function entry + // point, we want to use the entry map (-1), even if + // the first instruction of the function changes the + // stack map. + targetpc-- + pcdata = pcdatavalue(f, _PCDATA_StackMapIndex, targetpc, cache) + } + if pcdata == -1 { + // We do not have a valid pcdata value but there might be a + // stackmap for this function. It is likely that we are looking + // at the function prologue, assume so and hope for the best. + pcdata = 0 + } + + // Local variables. + size := frame.varp - frame.sp + var minsize uintptr + switch sys.ArchFamily { + case sys.ARM64: + minsize = sys.SpAlign + default: + minsize = sys.MinFrameSize + } + if size > minsize { + stackid := pcdata + stkmap := (*stackmap)(funcdata(f, _FUNCDATA_LocalsPointerMaps)) + if stkmap == nil || stkmap.n <= 0 { + print("runtime: frame ", funcname(f), " untyped locals ", hex(frame.varp-size), "+", hex(size), "\n") + throw("missing stackmap") + } + // If nbit == 0, there's no work to do. + if stkmap.nbit > 0 { + if stackid < 0 || stackid >= stkmap.n { + // don't know where we are + print("runtime: pcdata is ", stackid, " and ", stkmap.n, " locals stack map entries for ", funcname(f), " (targetpc=", hex(targetpc), ")\n") + throw("bad symbol table") + } + locals = stackmapdata(stkmap, stackid) + if stackDebug >= 3 && debug { + print(" locals ", stackid, "/", stkmap.n, " ", locals.n, " words ", locals.bytedata, "\n") + } + } else if stackDebug >= 3 && debug { + print(" no locals to adjust\n") + } + } + + // Arguments. + if frame.arglen > 0 { + if frame.argmap != nil { + // argmap is set when the function is reflect.makeFuncStub or reflect.methodValueCall. + // In this case, arglen specifies how much of the args section is actually live. + // (It could be either all the args + results, or just the args.) + args = *frame.argmap + n := int32(frame.arglen / sys.PtrSize) + if n < args.n { + args.n = n // Don't use more of the arguments than arglen. + } + } else { + stackmap := (*stackmap)(funcdata(f, _FUNCDATA_ArgsPointerMaps)) + if stackmap == nil || stackmap.n <= 0 { + print("runtime: frame ", funcname(f), " untyped args ", hex(frame.argp), "+", hex(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=", hex(targetpc), ")\n") + throw("bad symbol table") + } + if stackmap.nbit > 0 { + args = stackmapdata(stackmap, pcdata) + } + } + } + + // stack objects. + p := funcdata(f, _FUNCDATA_StackObjects) + if p != nil { + n := *(*uintptr)(p) + p = add(p, sys.PtrSize) + *(*slice)(unsafe.Pointer(&objs)) = slice{array: noescape(p), len: int(n), cap: int(n)} + // Note: the noescape above is needed to keep + // getStackMap from "leaking param content: + // frame". That leak propagates up to getgcmask, then + // GCMask, then verifyGCInfo, which converts the stack + // gcinfo tests into heap gcinfo tests :( + } + + return +} + +// A stackObjectRecord is generated by the compiler for each stack object in a stack frame. +// This record must match the generator code in cmd/compile/internal/gc/ssa.go:emitStackObjects. +type stackObjectRecord struct { + // offset in frame + // if negative, offset from varp + // if non-negative, offset from argp + off int + typ *_type +} + +// This is exported as ABI0 via linkname so obj can call it. +// +//go:nosplit +//go:linkname morestackc +func morestackc() { + throw("attempt to execute system stack code on user stack") +} |