github.com/gocuntian/go@v0.0.0-20160610041250-fee02d270bf8/src/cmd/vet/cgo.go (about)

     1  // Copyright 2015 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  // Check for invalid cgo pointer passing.
     6  // This looks for code that uses cgo to call C code passing values
     7  // whose types are almost always invalid according to the cgo pointer
     8  // sharing rules.
     9  // Specifically, it warns about attempts to pass a Go chan, map, func,
    10  // or slice to C, either directly, or via a pointer, array, or struct.
    11  
    12  package main
    13  
    14  import (
    15  	"go/ast"
    16  	"go/token"
    17  	"go/types"
    18  )
    19  
    20  func init() {
    21  	register("cgocall",
    22  		"check for types that may not be passed to cgo calls",
    23  		checkCgoCall,
    24  		callExpr)
    25  }
    26  
    27  func checkCgoCall(f *File, node ast.Node) {
    28  	x := node.(*ast.CallExpr)
    29  
    30  	// We are only looking for calls to functions imported from
    31  	// the "C" package.
    32  	sel, ok := x.Fun.(*ast.SelectorExpr)
    33  	if !ok {
    34  		return
    35  	}
    36  	id, ok := sel.X.(*ast.Ident)
    37  	if !ok || id.Name != "C" {
    38  		return
    39  	}
    40  
    41  	for _, arg := range x.Args {
    42  		if !typeOKForCgoCall(cgoBaseType(f, arg)) {
    43  			f.Badf(arg.Pos(), "possibly passing Go type with embedded pointer to C")
    44  		}
    45  
    46  		// Check for passing the address of a bad type.
    47  		if conv, ok := arg.(*ast.CallExpr); ok && len(conv.Args) == 1 && f.hasBasicType(conv.Fun, types.UnsafePointer) {
    48  			arg = conv.Args[0]
    49  		}
    50  		if u, ok := arg.(*ast.UnaryExpr); ok && u.Op == token.AND {
    51  			if !typeOKForCgoCall(cgoBaseType(f, u.X)) {
    52  				f.Badf(arg.Pos(), "possibly passing Go type with embedded pointer to C")
    53  			}
    54  		}
    55  	}
    56  }
    57  
    58  // cgoBaseType tries to look through type conversions involving
    59  // unsafe.Pointer to find the real type. It converts:
    60  //   unsafe.Pointer(x) => x
    61  //   *(*unsafe.Pointer)(unsafe.Pointer(&x)) => x
    62  func cgoBaseType(f *File, arg ast.Expr) types.Type {
    63  	switch arg := arg.(type) {
    64  	case *ast.CallExpr:
    65  		if len(arg.Args) == 1 && f.hasBasicType(arg.Fun, types.UnsafePointer) {
    66  			return cgoBaseType(f, arg.Args[0])
    67  		}
    68  	case *ast.StarExpr:
    69  		call, ok := arg.X.(*ast.CallExpr)
    70  		if !ok || len(call.Args) != 1 {
    71  			break
    72  		}
    73  		// Here arg is *f(v).
    74  		t := f.pkg.types[call.Fun].Type
    75  		if t == nil {
    76  			break
    77  		}
    78  		ptr, ok := t.Underlying().(*types.Pointer)
    79  		if !ok {
    80  			break
    81  		}
    82  		// Here arg is *(*p)(v)
    83  		elem, ok := ptr.Elem().Underlying().(*types.Basic)
    84  		if !ok || elem.Kind() != types.UnsafePointer {
    85  			break
    86  		}
    87  		// Here arg is *(*unsafe.Pointer)(v)
    88  		call, ok = call.Args[0].(*ast.CallExpr)
    89  		if !ok || len(call.Args) != 1 {
    90  			break
    91  		}
    92  		// Here arg is *(*unsafe.Pointer)(f(v))
    93  		if !f.hasBasicType(call.Fun, types.UnsafePointer) {
    94  			break
    95  		}
    96  		// Here arg is *(*unsafe.Pointer)(unsafe.Pointer(v))
    97  		u, ok := call.Args[0].(*ast.UnaryExpr)
    98  		if !ok || u.Op != token.AND {
    99  			break
   100  		}
   101  		// Here arg is *(*unsafe.Pointer)(unsafe.Pointer(&v))
   102  		return cgoBaseType(f, u.X)
   103  	}
   104  
   105  	return f.pkg.types[arg].Type
   106  }
   107  
   108  // typeOKForCgoCall returns true if the type of arg is OK to pass to a
   109  // C function using cgo. This is not true for Go types with embedded
   110  // pointers.
   111  func typeOKForCgoCall(t types.Type) bool {
   112  	if t == nil {
   113  		return true
   114  	}
   115  	switch t := t.Underlying().(type) {
   116  	case *types.Chan, *types.Map, *types.Signature, *types.Slice:
   117  		return false
   118  	case *types.Pointer:
   119  		return typeOKForCgoCall(t.Elem())
   120  	case *types.Array:
   121  		return typeOKForCgoCall(t.Elem())
   122  	case *types.Struct:
   123  		for i := 0; i < t.NumFields(); i++ {
   124  			if !typeOKForCgoCall(t.Field(i).Type()) {
   125  				return false
   126  			}
   127  		}
   128  	}
   129  	return true
   130  }