call.go

     1  // Copyright 2018 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package escape
     6  
     7  import (
     8  	"cmd/compile/internal/base"
     9  	"cmd/compile/internal/ir"
    10  	"cmd/compile/internal/typecheck"
    11  	"cmd/compile/internal/types"
    12  	"cmd/internal/src"
    13  	"strings"
    14  )
    15  
    16  // call evaluates a call expressions, including builtin calls. ks
    17  // should contain the holes representing where the function callee's
    18  // results flows.
    19  func (e *escape) call(ks []hole, call ir.Node) {
    20  	argument := func(k hole, arg ir.Node) {
    21  		// TODO(mdempsky): Should be "call argument".
    22  		e.expr(k.note(call, "call parameter"), arg)
    23  	}
    24  
    25  	switch call.Op() {
    26  	default:
    27  		ir.Dump("esc", call)
    28  		base.Fatalf("unexpected call op: %v", call.Op())
    29  
    30  	case ir.OCALLFUNC, ir.OCALLINTER:
    31  		call := call.(*ir.CallExpr)
    32  		typecheck.AssertFixedCall(call)
    33  
    34  		// Pick out the function callee, if statically known.
    35  		//
    36  		// TODO(mdempsky): Change fn from *ir.Name to *ir.Func, but some
    37  		// functions (e.g., runtime builtins, method wrappers, generated
    38  		// eq/hash functions) don't have it set. Investigate whether
    39  		// that's a concern.
    40  		var fn *ir.Name
    41  		switch call.Op() {
    42  		case ir.OCALLFUNC:
    43  			v := ir.StaticValue(call.Fun)
    44  			fn = ir.StaticCalleeName(v)
    45  		}
    46  
    47  		fntype := call.Fun.Type()
    48  		if fn != nil {
    49  			fntype = fn.Type()
    50  		}
    51  
    52  		if ks != nil && fn != nil && e.inMutualBatch(fn) {
    53  			for i, result := range fn.Type().Results() {
    54  				e.expr(ks[i], result.Nname.(*ir.Name))
    55  			}
    56  		}
    57  
    58  		var recvArg ir.Node
    59  		if call.Op() == ir.OCALLFUNC {
    60  			// Evaluate callee function expression.
    61  			calleeK := e.discardHole()
    62  			if fn == nil { // unknown callee
    63  				for _, k := range ks {
    64  					if k.dst != &e.blankLoc {
    65  						// The results flow somewhere, but we don't statically
    66  						// know the callee function. If a closure flows here, we
    67  						// need to conservatively assume its results might flow to
    68  						// the heap.
    69  						calleeK = e.calleeHole().note(call, "callee operand")
    70  						break
    71  					}
    72  				}
    73  			}
    74  			e.expr(calleeK, call.Fun)
    75  		} else {
    76  			recvArg = call.Fun.(*ir.SelectorExpr).X
    77  		}
    78  
    79  		// argumentParam handles escape analysis of assigning a call
    80  		// argument to its corresponding parameter.
    81  		argumentParam := func(param *types.Field, arg ir.Node) {
    82  			e.rewriteArgument(arg, call, fn)
    83  			argument(e.tagHole(ks, fn, param), arg)
    84  		}
    85  
    86  		// hash/maphash.escapeForHash forces its argument to be on
    87  		// the heap, if it contains a non-string pointer. We cannot
    88  		// hash pointers to local variables, as the address of the
    89  		// local variable might change on stack growth.
    90  		// Strings are okay as the hash depends on only the content,
    91  		// not the pointer.
    92  		// The actual call we match is
    93  		//   hash/maphash.escapeForHash[go.shape.T](dict, go.shape.T)
    94  		if fn != nil && fn.Sym().Pkg.Path == "hash/maphash" && strings.HasPrefix(fn.Sym().Name, "escapeForHash[") {
    95  			ps := fntype.Params()
    96  			if len(ps) == 2 && ps[1].Type.IsShape() {
    97  				if !hasNonStringPointers(ps[1].Type) {
    98  					argumentParam = func(param *types.Field, arg ir.Node) {
    99  						argument(e.discardHole(), arg)
   100  					}
   101  				} else {
   102  					argumentParam = func(param *types.Field, arg ir.Node) {
   103  						argument(e.heapHole(), arg)
   104  					}
   105  				}
   106  			}
   107  		}
   108  
   109  		args := call.Args
   110  		if recvParam := fntype.Recv(); recvParam != nil {
   111  			if recvArg == nil {
   112  				// Function call using method expression. Receiver argument is
   113  				// at the front of the regular arguments list.
   114  				recvArg, args = args[0], args[1:]
   115  			}
   116  
   117  			argumentParam(recvParam, recvArg)
   118  		}
   119  
   120  		for i, param := range fntype.Params() {
   121  			argumentParam(param, args[i])
   122  		}
   123  
   124  	case ir.OINLCALL:
   125  		call := call.(*ir.InlinedCallExpr)
   126  		e.stmts(call.Body)
   127  		for i, result := range call.ReturnVars {
   128  			k := e.discardHole()
   129  			if ks != nil {
   130  				k = ks[i]
   131  			}
   132  			e.expr(k, result)
   133  		}
   134  
   135  	case ir.OAPPEND:
   136  		call := call.(*ir.CallExpr)
   137  		args := call.Args
   138  
   139  		// Appendee slice may flow directly to the result, if
   140  		// it has enough capacity. Alternatively, a new heap
   141  		// slice might be allocated, and all slice elements
   142  		// might flow to heap.
   143  		appendeeK := e.teeHole(ks[0], e.mutatorHole())
   144  		if args[0].Type().Elem().HasPointers() {
   145  			appendeeK = e.teeHole(appendeeK, e.heapHole().deref(call, "appendee slice"))
   146  		}
   147  		argument(appendeeK, args[0])
   148  
   149  		if call.IsDDD {
   150  			appendedK := e.discardHole()
   151  			if args[1].Type().IsSlice() && args[1].Type().Elem().HasPointers() {
   152  				appendedK = e.heapHole().deref(call, "appended slice...")
   153  			}
   154  			argument(appendedK, args[1])
   155  		} else {
   156  			for i := 1; i < len(args); i++ {
   157  				argument(e.heapHole(), args[i])
   158  			}
   159  		}
   160  		e.discard(call.RType)
   161  
   162  	case ir.OCOPY:
   163  		call := call.(*ir.BinaryExpr)
   164  		argument(e.mutatorHole(), call.X)
   165  
   166  		copiedK := e.discardHole()
   167  		if call.Y.Type().IsSlice() && call.Y.Type().Elem().HasPointers() {
   168  			copiedK = e.heapHole().deref(call, "copied slice")
   169  		}
   170  		argument(copiedK, call.Y)
   171  		e.discard(call.RType)
   172  
   173  	case ir.OPANIC:
   174  		call := call.(*ir.UnaryExpr)
   175  		argument(e.heapHole(), call.X)
   176  
   177  	case ir.OCOMPLEX:
   178  		call := call.(*ir.BinaryExpr)
   179  		e.discard(call.X)
   180  		e.discard(call.Y)
   181  
   182  	case ir.ODELETE, ir.OPRINT, ir.OPRINTLN, ir.ORECOVERFP:
   183  		call := call.(*ir.CallExpr)
   184  		for _, arg := range call.Args {
   185  			e.discard(arg)
   186  		}
   187  		e.discard(call.RType)
   188  
   189  	case ir.OMIN, ir.OMAX:
   190  		call := call.(*ir.CallExpr)
   191  		for _, arg := range call.Args {
   192  			argument(ks[0], arg)
   193  		}
   194  		e.discard(call.RType)
   195  
   196  	case ir.OLEN, ir.OCAP, ir.OREAL, ir.OIMAG, ir.OCLOSE:
   197  		call := call.(*ir.UnaryExpr)
   198  		e.discard(call.X)
   199  
   200  	case ir.OCLEAR:
   201  		call := call.(*ir.UnaryExpr)
   202  		argument(e.mutatorHole(), call.X)
   203  
   204  	case ir.OUNSAFESTRINGDATA, ir.OUNSAFESLICEDATA:
   205  		call := call.(*ir.UnaryExpr)
   206  		argument(ks[0], call.X)
   207  
   208  	case ir.OUNSAFEADD, ir.OUNSAFESLICE, ir.OUNSAFESTRING:
   209  		call := call.(*ir.BinaryExpr)
   210  		argument(ks[0], call.X)
   211  		e.discard(call.Y)
   212  		e.discard(call.RType)
   213  	}
   214  }
   215  
   216  // goDeferStmt analyzes a "go" or "defer" statement.
   217  func (e *escape) goDeferStmt(n *ir.GoDeferStmt) {
   218  	k := e.heapHole()
   219  	if n.Op() == ir.ODEFER && e.loopDepth == 1 && n.DeferAt == nil {
   220  		// Top-level defer arguments don't escape to the heap,
   221  		// but they do need to last until they're invoked.
   222  		k = e.later(e.discardHole())
   223  
   224  		// force stack allocation of defer record, unless
   225  		// open-coded defers are used (see ssa.go)
   226  		n.SetEsc(ir.EscNever)
   227  	}
   228  
   229  	// If the function is already a zero argument/result function call,
   230  	// just escape analyze it normally.
   231  	//
   232  	// Note that the runtime is aware of this optimization for
   233  	// "go" statements that start in reflect.makeFuncStub or
   234  	// reflect.methodValueCall.
   235  
   236  	call, ok := n.Call.(*ir.CallExpr)
   237  	if !ok || call.Op() != ir.OCALLFUNC {
   238  		base.FatalfAt(n.Pos(), "expected function call: %v", n.Call)
   239  	}
   240  	if sig := call.Fun.Type(); sig.NumParams()+sig.NumResults() != 0 {
   241  		base.FatalfAt(n.Pos(), "expected signature without parameters or results: %v", sig)
   242  	}
   243  
   244  	if clo, ok := call.Fun.(*ir.ClosureExpr); ok && n.Op() == ir.OGO {
   245  		clo.IsGoWrap = true
   246  	}
   247  
   248  	e.expr(k, call.Fun)
   249  }
   250  
   251  // rewriteArgument rewrites the argument arg of the given call expression.
   252  // fn is the static callee function, if known.
   253  func (e *escape) rewriteArgument(arg ir.Node, call *ir.CallExpr, fn *ir.Name) {
   254  	if fn == nil || fn.Func == nil {
   255  		return
   256  	}
   257  	pragma := fn.Func.Pragma
   258  	if pragma&(ir.UintptrKeepAlive|ir.UintptrEscapes) == 0 {
   259  		return
   260  	}
   261  
   262  	// unsafeUintptr rewrites "uintptr(ptr)" arguments to syscall-like
   263  	// functions, so that ptr is kept alive and/or escaped as
   264  	// appropriate. unsafeUintptr also reports whether it modified arg0.
   265  	unsafeUintptr := func(arg ir.Node) {
   266  		// If the argument is really a pointer being converted to uintptr,
   267  		// arrange for the pointer to be kept alive until the call
   268  		// returns, by copying it into a temp and marking that temp still
   269  		// alive when we pop the temp stack.
   270  		conv, ok := arg.(*ir.ConvExpr)
   271  		if !ok || conv.Op() != ir.OCONVNOP {
   272  			return // not a conversion
   273  		}
   274  		if !conv.X.Type().IsUnsafePtr() || !conv.Type().IsUintptr() {
   275  			return // not an unsafe.Pointer->uintptr conversion
   276  		}
   277  
   278  		// Create and declare a new pointer-typed temp variable.
   279  		//
   280  		// TODO(mdempsky): This potentially violates the Go spec's order
   281  		// of evaluations, by evaluating arg.X before any other
   282  		// operands.
   283  		tmp := e.copyExpr(conv.Pos(), conv.X, call.PtrInit())
   284  		conv.X = tmp
   285  
   286  		k := e.mutatorHole()
   287  		if pragma&ir.UintptrEscapes != 0 {
   288  			k = e.heapHole().note(conv, "//go:uintptrescapes")
   289  		}
   290  		e.flow(k, e.oldLoc(tmp))
   291  
   292  		if pragma&ir.UintptrKeepAlive != 0 {
   293  			tmp.SetAddrtaken(true) // ensure SSA keeps the tmp variable
   294  			call.KeepAlive = append(call.KeepAlive, tmp)
   295  		}
   296  	}
   297  
   298  	// For variadic functions, the compiler has already rewritten:
   299  	//
   300  	//     f(a, b, c)
   301  	//
   302  	// to:
   303  	//
   304  	//     f([]T{a, b, c}...)
   305  	//
   306  	// So we need to look into slice elements to handle uintptr(ptr)
   307  	// arguments to variadic syscall-like functions correctly.
   308  	if arg.Op() == ir.OSLICELIT {
   309  		list := arg.(*ir.CompLitExpr).List
   310  		for _, el := range list {
   311  			if el.Op() == ir.OKEY {
   312  				el = el.(*ir.KeyExpr).Value
   313  			}
   314  			unsafeUintptr(el)
   315  		}
   316  	} else {
   317  		unsafeUintptr(arg)
   318  	}
   319  }
   320  
   321  // copyExpr creates and returns a new temporary variable within fn;
   322  // appends statements to init to declare and initialize it to expr;
   323  // and escape analyzes the data flow.
   324  func (e *escape) copyExpr(pos src.XPos, expr ir.Node, init *ir.Nodes) *ir.Name {
   325  	if ir.HasUniquePos(expr) {
   326  		pos = expr.Pos()
   327  	}
   328  
   329  	tmp := typecheck.TempAt(pos, e.curfn, expr.Type())
   330  
   331  	stmts := []ir.Node{
   332  		ir.NewDecl(pos, ir.ODCL, tmp),
   333  		ir.NewAssignStmt(pos, tmp, expr),
   334  	}
   335  	typecheck.Stmts(stmts)
   336  	init.Append(stmts...)
   337  
   338  	e.newLoc(tmp, true)
   339  	e.stmts(stmts)
   340  
   341  	return tmp
   342  }
   343  
   344  // tagHole returns a hole for evaluating an argument passed to param.
   345  // ks should contain the holes representing where the function
   346  // callee's results flows. fn is the statically-known callee function,
   347  // if any.
   348  func (e *escape) tagHole(ks []hole, fn *ir.Name, param *types.Field) hole {
   349  	// If this is a dynamic call, we can't rely on param.Note.
   350  	if fn == nil {
   351  		return e.heapHole()
   352  	}
   353  
   354  	if e.inMutualBatch(fn) {
   355  		if param.Nname == nil {
   356  			return e.discardHole()
   357  		}
   358  		return e.addr(param.Nname.(*ir.Name))
   359  	}
   360  
   361  	// Call to previously tagged function.
   362  
   363  	var tagKs []hole
   364  	esc := parseLeaks(param.Note)
   365  
   366  	if x := esc.Heap(); x >= 0 {
   367  		tagKs = append(tagKs, e.heapHole().shift(x))
   368  	}
   369  	if x := esc.Mutator(); x >= 0 {
   370  		tagKs = append(tagKs, e.mutatorHole().shift(x))
   371  	}
   372  	if x := esc.Callee(); x >= 0 {
   373  		tagKs = append(tagKs, e.calleeHole().shift(x))
   374  	}
   375  
   376  	if ks != nil {
   377  		for i := 0; i < numEscResults; i++ {
   378  			if x := esc.Result(i); x >= 0 {
   379  				tagKs = append(tagKs, ks[i].shift(x))
   380  			}
   381  		}
   382  	}
   383  
   384  	return e.teeHole(tagKs...)
   385  }
   386  
   387  func hasNonStringPointers(t *types.Type) bool {
   388  	if !t.HasPointers() {
   389  		return false
   390  	}
   391  	switch t.Kind() {
   392  	case types.TSTRING:
   393  		return false
   394  	case types.TSTRUCT:
   395  		for _, f := range t.Fields() {
   396  			if hasNonStringPointers(f.Type) {
   397  				return true
   398  			}
   399  		}
   400  		return false
   401  	case types.TARRAY:
   402  		return hasNonStringPointers(t.Elem())
   403  	}
   404  	return true
   405  }
   406
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