| // Copyright 2011 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 gc |
| |
| import ( |
| "cmd/compile/internal/types" |
| "fmt" |
| ) |
| |
| func escapes(all []*Node) { |
| visitBottomUp(all, escapeFuncs) |
| } |
| |
| const ( |
| EscFuncUnknown = 0 + iota |
| EscFuncPlanned |
| EscFuncStarted |
| EscFuncTagged |
| ) |
| |
| func min8(a, b int8) int8 { |
| if a < b { |
| return a |
| } |
| return b |
| } |
| |
| func max8(a, b int8) int8 { |
| if a > b { |
| return a |
| } |
| return b |
| } |
| |
| const ( |
| EscUnknown = iota |
| EscNone // Does not escape to heap, result, or parameters. |
| EscHeap // Reachable from the heap |
| EscNever // By construction will not escape. |
| ) |
| |
| // funcSym returns fn.Func.Nname.Sym if no nils are encountered along the way. |
| func funcSym(fn *Node) *types.Sym { |
| if fn == nil || fn.Func.Nname == nil { |
| return nil |
| } |
| return fn.Func.Nname.Sym |
| } |
| |
| // Mark labels that have no backjumps to them as not increasing e.loopdepth. |
| // Walk hasn't generated (goto|label).Left.Sym.Label yet, so we'll cheat |
| // and set it to one of the following two. Then in esc we'll clear it again. |
| var ( |
| looping Node |
| nonlooping Node |
| ) |
| |
| func isSliceSelfAssign(dst, src *Node) bool { |
| // Detect the following special case. |
| // |
| // func (b *Buffer) Foo() { |
| // n, m := ... |
| // b.buf = b.buf[n:m] |
| // } |
| // |
| // This assignment is a no-op for escape analysis, |
| // it does not store any new pointers into b that were not already there. |
| // However, without this special case b will escape, because we assign to OIND/ODOTPTR. |
| // Here we assume that the statement will not contain calls, |
| // that is, that order will move any calls to init. |
| // Otherwise base ONAME value could change between the moments |
| // when we evaluate it for dst and for src. |
| |
| // dst is ONAME dereference. |
| if dst.Op != ODEREF && dst.Op != ODOTPTR || dst.Left.Op != ONAME { |
| return false |
| } |
| // src is a slice operation. |
| switch src.Op { |
| case OSLICE, OSLICE3, OSLICESTR: |
| // OK. |
| case OSLICEARR, OSLICE3ARR: |
| // Since arrays are embedded into containing object, |
| // slice of non-pointer array will introduce a new pointer into b that was not already there |
| // (pointer to b itself). After such assignment, if b contents escape, |
| // b escapes as well. If we ignore such OSLICEARR, we will conclude |
| // that b does not escape when b contents do. |
| // |
| // Pointer to an array is OK since it's not stored inside b directly. |
| // For slicing an array (not pointer to array), there is an implicit OADDR. |
| // We check that to determine non-pointer array slicing. |
| if src.Left.Op == OADDR { |
| return false |
| } |
| default: |
| return false |
| } |
| // slice is applied to ONAME dereference. |
| if src.Left.Op != ODEREF && src.Left.Op != ODOTPTR || src.Left.Left.Op != ONAME { |
| return false |
| } |
| // dst and src reference the same base ONAME. |
| return dst.Left == src.Left.Left |
| } |
| |
| // isSelfAssign reports whether assignment from src to dst can |
| // be ignored by the escape analysis as it's effectively a self-assignment. |
| func isSelfAssign(dst, src *Node) bool { |
| if isSliceSelfAssign(dst, src) { |
| return true |
| } |
| |
| // Detect trivial assignments that assign back to the same object. |
| // |
| // It covers these cases: |
| // val.x = val.y |
| // val.x[i] = val.y[j] |
| // val.x1.x2 = val.x1.y2 |
| // ... etc |
| // |
| // These assignments do not change assigned object lifetime. |
| |
| if dst == nil || src == nil || dst.Op != src.Op { |
| return false |
| } |
| |
| switch dst.Op { |
| case ODOT, ODOTPTR: |
| // Safe trailing accessors that are permitted to differ. |
| case OINDEX: |
| if mayAffectMemory(dst.Right) || mayAffectMemory(src.Right) { |
| return false |
| } |
| default: |
| return false |
| } |
| |
| // The expression prefix must be both "safe" and identical. |
| return samesafeexpr(dst.Left, src.Left) |
| } |
| |
| // mayAffectMemory reports whether evaluation of n may affect the program's |
| // memory state. If the expression can't affect memory state, then it can be |
| // safely ignored by the escape analysis. |
| func mayAffectMemory(n *Node) bool { |
| // We may want to use a list of "memory safe" ops instead of generally |
| // "side-effect free", which would include all calls and other ops that can |
| // allocate or change global state. For now, it's safer to start with the latter. |
| // |
| // We're ignoring things like division by zero, index out of range, |
| // and nil pointer dereference here. |
| switch n.Op { |
| case ONAME, OCLOSUREVAR, OLITERAL: |
| return false |
| |
| // Left+Right group. |
| case OINDEX, OADD, OSUB, OOR, OXOR, OMUL, OLSH, ORSH, OAND, OANDNOT, ODIV, OMOD: |
| return mayAffectMemory(n.Left) || mayAffectMemory(n.Right) |
| |
| // Left group. |
| case ODOT, ODOTPTR, ODEREF, OCONVNOP, OCONV, OLEN, OCAP, |
| ONOT, OBITNOT, OPLUS, ONEG, OALIGNOF, OOFFSETOF, OSIZEOF: |
| return mayAffectMemory(n.Left) |
| |
| default: |
| return true |
| } |
| } |
| |
| func mustHeapAlloc(n *Node) bool { |
| if n.Type == nil { |
| return false |
| } |
| |
| // Parameters are always passed via the stack. |
| if n.Op == ONAME && (n.Class() == PPARAM || n.Class() == PPARAMOUT) { |
| return false |
| } |
| |
| if n.Type.Width > maxStackVarSize { |
| return true |
| } |
| |
| if (n.Op == ONEW || n.Op == OPTRLIT) && n.Type.Elem().Width >= maxImplicitStackVarSize { |
| return true |
| } |
| |
| if n.Op == OMAKESLICE && !isSmallMakeSlice(n) { |
| return true |
| } |
| |
| return false |
| } |
| |
| // addrescapes tags node n as having had its address taken |
| // by "increasing" the "value" of n.Esc to EscHeap. |
| // Storage is allocated as necessary to allow the address |
| // to be taken. |
| func addrescapes(n *Node) { |
| switch n.Op { |
| default: |
| // Unexpected Op, probably due to a previous type error. Ignore. |
| |
| case ODEREF, ODOTPTR: |
| // Nothing to do. |
| |
| case ONAME: |
| if n == nodfp { |
| break |
| } |
| |
| // if this is a tmpname (PAUTO), it was tagged by tmpname as not escaping. |
| // on PPARAM it means something different. |
| if n.Class() == PAUTO && n.Esc == EscNever { |
| break |
| } |
| |
| // If a closure reference escapes, mark the outer variable as escaping. |
| if n.Name.IsClosureVar() { |
| addrescapes(n.Name.Defn) |
| break |
| } |
| |
| if n.Class() != PPARAM && n.Class() != PPARAMOUT && n.Class() != PAUTO { |
| break |
| } |
| |
| // This is a plain parameter or local variable that needs to move to the heap, |
| // but possibly for the function outside the one we're compiling. |
| // That is, if we have: |
| // |
| // func f(x int) { |
| // func() { |
| // global = &x |
| // } |
| // } |
| // |
| // then we're analyzing the inner closure but we need to move x to the |
| // heap in f, not in the inner closure. Flip over to f before calling moveToHeap. |
| oldfn := Curfn |
| Curfn = n.Name.Curfn |
| if Curfn.Func.Closure != nil && Curfn.Op == OCLOSURE { |
| Curfn = Curfn.Func.Closure |
| } |
| ln := lineno |
| lineno = Curfn.Pos |
| moveToHeap(n) |
| Curfn = oldfn |
| lineno = ln |
| |
| // ODOTPTR has already been introduced, |
| // so these are the non-pointer ODOT and OINDEX. |
| // In &x[0], if x is a slice, then x does not |
| // escape--the pointer inside x does, but that |
| // is always a heap pointer anyway. |
| case ODOT, OINDEX, OPAREN, OCONVNOP: |
| if !n.Left.Type.IsSlice() { |
| addrescapes(n.Left) |
| } |
| } |
| } |
| |
| // moveToHeap records the parameter or local variable n as moved to the heap. |
| func moveToHeap(n *Node) { |
| if Debug['r'] != 0 { |
| Dump("MOVE", n) |
| } |
| if compiling_runtime { |
| yyerror("%v escapes to heap, not allowed in runtime", n) |
| } |
| if n.Class() == PAUTOHEAP { |
| Dump("n", n) |
| Fatalf("double move to heap") |
| } |
| |
| // Allocate a local stack variable to hold the pointer to the heap copy. |
| // temp will add it to the function declaration list automatically. |
| heapaddr := temp(types.NewPtr(n.Type)) |
| heapaddr.Sym = lookup("&" + n.Sym.Name) |
| heapaddr.Orig.Sym = heapaddr.Sym |
| heapaddr.Pos = n.Pos |
| |
| // Unset AutoTemp to persist the &foo variable name through SSA to |
| // liveness analysis. |
| // TODO(mdempsky/drchase): Cleaner solution? |
| heapaddr.Name.SetAutoTemp(false) |
| |
| // Parameters have a local stack copy used at function start/end |
| // in addition to the copy in the heap that may live longer than |
| // the function. |
| if n.Class() == PPARAM || n.Class() == PPARAMOUT { |
| if n.Xoffset == BADWIDTH { |
| Fatalf("addrescapes before param assignment") |
| } |
| |
| // We rewrite n below to be a heap variable (indirection of heapaddr). |
| // Preserve a copy so we can still write code referring to the original, |
| // and substitute that copy into the function declaration list |
| // so that analyses of the local (on-stack) variables use it. |
| stackcopy := newname(n.Sym) |
| stackcopy.Type = n.Type |
| stackcopy.Xoffset = n.Xoffset |
| stackcopy.SetClass(n.Class()) |
| stackcopy.Name.Param.Heapaddr = heapaddr |
| if n.Class() == PPARAMOUT { |
| // Make sure the pointer to the heap copy is kept live throughout the function. |
| // The function could panic at any point, and then a defer could recover. |
| // Thus, we need the pointer to the heap copy always available so the |
| // post-deferreturn code can copy the return value back to the stack. |
| // See issue 16095. |
| heapaddr.Name.SetIsOutputParamHeapAddr(true) |
| } |
| n.Name.Param.Stackcopy = stackcopy |
| |
| // Substitute the stackcopy into the function variable list so that |
| // liveness and other analyses use the underlying stack slot |
| // and not the now-pseudo-variable n. |
| found := false |
| for i, d := range Curfn.Func.Dcl { |
| if d == n { |
| Curfn.Func.Dcl[i] = stackcopy |
| found = true |
| break |
| } |
| // Parameters are before locals, so can stop early. |
| // This limits the search even in functions with many local variables. |
| if d.Class() == PAUTO { |
| break |
| } |
| } |
| if !found { |
| Fatalf("cannot find %v in local variable list", n) |
| } |
| Curfn.Func.Dcl = append(Curfn.Func.Dcl, n) |
| } |
| |
| // Modify n in place so that uses of n now mean indirection of the heapaddr. |
| n.SetClass(PAUTOHEAP) |
| n.Xoffset = 0 |
| n.Name.Param.Heapaddr = heapaddr |
| n.Esc = EscHeap |
| if Debug['m'] != 0 { |
| Warnl(n.Pos, "moved to heap: %v", n) |
| } |
| } |
| |
| // This special tag is applied to uintptr variables |
| // that we believe may hold unsafe.Pointers for |
| // calls into assembly functions. |
| const unsafeUintptrTag = "unsafe-uintptr" |
| |
| // This special tag is applied to uintptr parameters of functions |
| // marked go:uintptrescapes. |
| const uintptrEscapesTag = "uintptr-escapes" |
| |
| func (e *Escape) paramTag(fn *Node, narg int, f *types.Field) string { |
| name := func() string { |
| if f.Sym != nil { |
| return f.Sym.Name |
| } |
| return fmt.Sprintf("arg#%d", narg) |
| } |
| |
| if fn.Nbody.Len() == 0 { |
| // Assume that uintptr arguments must be held live across the call. |
| // This is most important for syscall.Syscall. |
| // See golang.org/issue/13372. |
| // This really doesn't have much to do with escape analysis per se, |
| // but we are reusing the ability to annotate an individual function |
| // argument and pass those annotations along to importing code. |
| if f.Type.Etype == TUINTPTR { |
| if Debug['m'] != 0 { |
| Warnl(f.Pos, "assuming %v is unsafe uintptr", name()) |
| } |
| return unsafeUintptrTag |
| } |
| |
| if !types.Haspointers(f.Type) { // don't bother tagging for scalars |
| return "" |
| } |
| |
| var esc EscLeaks |
| |
| // External functions are assumed unsafe, unless |
| // //go:noescape is given before the declaration. |
| if fn.Func.Pragma&Noescape != 0 { |
| if Debug['m'] != 0 && f.Sym != nil { |
| Warnl(f.Pos, "%v does not escape", name()) |
| } |
| } else { |
| if Debug['m'] != 0 && f.Sym != nil { |
| Warnl(f.Pos, "leaking param: %v", name()) |
| } |
| esc.AddHeap(0) |
| } |
| |
| return esc.Encode() |
| } |
| |
| if fn.Func.Pragma&UintptrEscapes != 0 { |
| if f.Type.Etype == TUINTPTR { |
| if Debug['m'] != 0 { |
| Warnl(f.Pos, "marking %v as escaping uintptr", name()) |
| } |
| return uintptrEscapesTag |
| } |
| if f.IsDDD() && f.Type.Elem().Etype == TUINTPTR { |
| // final argument is ...uintptr. |
| if Debug['m'] != 0 { |
| Warnl(f.Pos, "marking %v as escaping ...uintptr", name()) |
| } |
| return uintptrEscapesTag |
| } |
| } |
| |
| if !types.Haspointers(f.Type) { // don't bother tagging for scalars |
| return "" |
| } |
| |
| // Unnamed parameters are unused and therefore do not escape. |
| if f.Sym == nil || f.Sym.IsBlank() { |
| var esc EscLeaks |
| return esc.Encode() |
| } |
| |
| n := asNode(f.Nname) |
| loc := e.oldLoc(n) |
| esc := loc.paramEsc |
| esc.Optimize() |
| |
| if Debug['m'] != 0 && !loc.escapes { |
| if esc.Empty() { |
| Warnl(f.Pos, "%v does not escape", name()) |
| } |
| if x := esc.Heap(); x >= 0 { |
| if x == 0 { |
| Warnl(f.Pos, "leaking param: %v", name()) |
| } else { |
| // TODO(mdempsky): Mention level=x like below? |
| Warnl(f.Pos, "leaking param content: %v", name()) |
| } |
| } |
| for i := 0; i < numEscResults; i++ { |
| if x := esc.Result(i); x >= 0 { |
| res := fn.Type.Results().Field(i).Sym |
| Warnl(f.Pos, "leaking param: %v to result %v level=%d", name(), res, x) |
| } |
| } |
| } |
| |
| return esc.Encode() |
| } |