cgo: various bug fixes

* remember #defined names, so that C.stdout can refer
  to the real name (on OS X) __stdoutp.
* better handling of #defined constant expressions
* allow n, err = C.strtol("asdf", 0, 123) to get errno as os.Error
* write all output files to current directory
* don't require gcc output if there was no input

Fixes #533.
Fixes #709.
Fixes #756.

R=r
CC=dho, golang-dev, iant
https://golang.org/cl/1734047

13 files changed, 1240 insertions, 651 deletions

diff --git a/misc/cgo/stdio/Makefile b/misc/cgo/stdio/Makefile
index 2e3d466318..a0093ff529 100644
--- a/misc/cgo/stdio/Makefile
+++ b/misc/cgo/stdio/Makefile
@@ -6,7 +6,9 @@ include ../../../src/Make.$(GOARCH)
 
 TARG=stdio
 CGOFILES=\
-	file.go
+	align.go\
+	file.go\
+	test.go\
 
 CLEANFILES+=hello fib chain run.out
 
diff --git a/misc/cgo/stdio/align.go b/misc/cgo/stdio/align.go
new file mode 100644
index 0000000000..6cdfd902f4
--- /dev/null
+++ b/misc/cgo/stdio/align.go
@@ -0,0 +1,78 @@
+package stdio
+
+/*
+#include <stdio.h>
+
+typedef unsigned char Uint8;
+typedef unsigned short Uint16;
+
+typedef enum {
+ MOD1 = 0x0000,
+ MODX = 0x8000
+} SDLMod;
+
+typedef enum {
+ A = 1,
+ B = 322,
+ SDLK_LAST
+} SDLKey;
+
+typedef struct SDL_keysym {
+	Uint8 scancode;
+	SDLKey sym;
+	SDLMod mod;
+	Uint16 unicode;
+} SDL_keysym;
+
+typedef struct SDL_KeyboardEvent {
+	Uint8 typ;
+	Uint8 which;
+	Uint8 state;
+	SDL_keysym keysym;
+} SDL_KeyboardEvent;
+
+void makeEvent(SDL_KeyboardEvent *event) {
+ unsigned char *p;
+ int i;
+
+ p = (unsigned char*)event;
+ for (i=0; i<sizeof *event; i++) {
+   p[i] = i;
+ }
+}
+
+int same(SDL_KeyboardEvent* e, Uint8 typ, Uint8 which, Uint8 state, Uint8 scan, SDLKey sym, SDLMod mod, Uint16 uni) {
+  return e->typ == typ && e->which == which && e->state == state && e->keysym.scancode == scan && e->keysym.sym == sym && e->keysym.mod == mod && e->keysym.unicode == uni;
+}
+
+void cTest(SDL_KeyboardEvent *event) {
+ printf("C: %#x %#x %#x %#x %#x %#x %#x\n", event->typ, event->which, event->state,
+   event->keysym.scancode, event->keysym.sym, event->keysym.mod, event->keysym.unicode);
+ fflush(stdout);
+}
+
+*/
+import "C"
+
+import (
+	"fmt"
+	"syscall"
+)
+
+func TestAlign() {
+	if syscall.ARCH == "amd64" {
+		// alignment is known to be broken on amd64.
+		// http://code.google.com/p/go/issues/detail?id=609
+		return
+	}
+	var evt C.SDL_KeyboardEvent
+	C.makeEvent(&evt)
+	if C.same(&evt, evt.typ, evt.which, evt.state, evt.keysym.scancode, evt.keysym.sym, evt.keysym.mod, evt.keysym.unicode) == 0 {
+		fmt.Println("*** bad alignment")
+		C.cTest(&evt)
+		fmt.Printf("Go: %#x %#x %#x %#x %#x %#x %#x\n",
+			evt.typ, evt.which, evt.state, evt.keysym.scancode,
+			evt.keysym.sym, evt.keysym.mod, evt.keysym.unicode)
+		fmt.Println(evt)
+	}
+}
diff --git a/misc/cgo/stdio/chain.go b/misc/cgo/stdio/chain.go
index dd5e01542b..c2b105072e 100644
--- a/misc/cgo/stdio/chain.go
+++ b/misc/cgo/stdio/chain.go
@@ -22,7 +22,7 @@ func link(left chan<- int, right <-chan int) {
 	runtime.LockOSThread()
 	for {
 		v := <-right
-		stdio.Puts(strconv.Itoa(v))
+		stdio.Stdout.WriteString(strconv.Itoa(v) + "\n")
 		left <- 1+v
 	}
 }
@@ -38,6 +38,6 @@ func main() {
 	for i := 0; i < R; i++ {
 		right <- 0
 		x := <-leftmost
-		stdio.Puts(strconv.Itoa(x))
+		stdio.Stdout.WriteString(strconv.Itoa(x) + "\n")
 	}
 }
diff --git a/misc/cgo/stdio/fib.go b/misc/cgo/stdio/fib.go
index 63ae049886..c02e31fd8d 100644
--- a/misc/cgo/stdio/fib.go
+++ b/misc/cgo/stdio/fib.go
@@ -26,7 +26,7 @@ func fibber(c, out chan int64, i int64) {
 	}
 	for {
 		j := <-c
-		stdio.Puts(strconv.Itoa64(j))
+		stdio.Stdout.WriteString(strconv.Itoa64(j) + "\n")
 		out <- j
 		<-out
 		i += j
diff --git a/misc/cgo/stdio/file.go b/misc/cgo/stdio/file.go
index 7d1f222805..1f461f2939 100644
--- a/misc/cgo/stdio/file.go
+++ b/misc/cgo/stdio/file.go
@@ -10,33 +10,31 @@ see ../gmp/gmp.go.
 
 package stdio
 
-// TODO(rsc): Remove fflushstdout when C.fflush(C.stdout) works in cgo.
-
 /*
 #include <stdio.h>
 #include <stdlib.h>
+#include <sys/stat.h>
+#include <errno.h>
 
-void fflushstdout(void) { fflush(stdout); }
+char* greeting = "hello, world";
 */
 import "C"
 import "unsafe"
 
-/*
 type File C.FILE
 
 var Stdout = (*File)(C.stdout)
 var Stderr = (*File)(C.stderr)
 
 func (f *File) WriteString(s string) {
-	p := C.CString(s);
-	C.fputs(p, (*C.FILE)(f));
-	C.free(p);
-}
-*/
-
-func Puts(s string) {
 	p := C.CString(s)
-	C.puts(p)
+	C.fputs(p, (*C.FILE)(f))
 	C.free(unsafe.Pointer(p))
-	C.fflushstdout()
+	f.Flush()
+}
+
+func (f *File) Flush() {
+	C.fflush((*C.FILE)(f))
 }
+
+var Greeting = C.GoString(C.greeting)
diff --git a/misc/cgo/stdio/hello.go b/misc/cgo/stdio/hello.go
index 47f9de02f1..9cb6e6884c 100644
--- a/misc/cgo/stdio/hello.go
+++ b/misc/cgo/stdio/hello.go
@@ -4,9 +4,26 @@
 
 package main
 
-import "stdio"
+import (
+	"os"
+	"stdio"
+)
 
 func main() {
-	//	stdio.Stdout.WriteString("hello, world\n");
-	stdio.Puts("hello, world")
+	stdio.Stdout.WriteString(stdio.Greeting + "\n")
+
+	l := stdio.Atol("123")
+	if l != 123 {
+		println("Atol 123: ", l)
+		panic("bad atol")
+	}
+
+	n, err := stdio.Strtol("asdf", 123)
+	if n != 0 || err != os.EINVAL {
+		println("Strtol: ", n, err)
+		panic("bad atoi2")
+	}
+
+	stdio.TestAlign()
+	stdio.TestEnum()
 }
diff --git a/misc/cgo/stdio/test.go b/misc/cgo/stdio/test.go
new file mode 100644
index 0000000000..490eb93c64
--- /dev/null
+++ b/misc/cgo/stdio/test.go
@@ -0,0 +1,91 @@
+// Copyright 2010 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.
+
+// This file contains test cases for cgo.
+
+package stdio
+
+/*
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <errno.h>
+
+#define SHIFT(x, y)  ((x)<<(y))
+#define KILO SHIFT(1, 10)
+
+enum {
+	Enum1 = 1,
+	Enum2 = 2,
+};
+*/
+import "C"
+import (
+	"os"
+	"unsafe"
+)
+
+const EINVAL = C.EINVAL /* test #define */
+
+var KILO = C.KILO
+
+func Size(name string) (int64, os.Error) {
+	var st C.struct_stat
+	p := C.CString(name)
+	_, err := C.stat(p, &st)
+	C.free(unsafe.Pointer(p))
+	if err != nil {
+		return 0, err
+	}
+	return int64(C.ulong(st.st_size)), nil
+}
+
+func Strtol(s string, base int) (int, os.Error) {
+	p := C.CString(s)
+	n, err := C.strtol(p, nil, C.int(base))
+	C.free(unsafe.Pointer(p))
+	return int(n), err
+}
+
+func Atol(s string) int {
+	p := C.CString(s)
+	n := C.atol(p)
+	C.free(unsafe.Pointer(p))
+	return int(n)
+}
+
+func TestEnum() {
+	if C.Enum1 != 1 || C.Enum2 != 2 {
+		println("bad enum", C.Enum1, C.Enum2)
+	}
+}
+
+func TestAtol() {
+	l := Atol("123")
+	if l != 123 {
+		println("Atol 123: ", l)
+		panic("bad atol")
+	}
+}
+
+func TestErrno() {
+	n, err := Strtol("asdf", 123)
+	if n != 0 || err != os.EINVAL {
+		println("Strtol: ", n, err)
+		panic("bad atoi2")
+	}
+}
+
+var (
+	uint  = (C.uint)(0)
+	ulong C.ulong
+	char  C.char
+)
+
+func Test() {
+	TestAlign()
+	TestAtol()
+	TestEnum()
+	TestErrno()
+}
diff --git a/src/cmd/cgo/ast.go b/src/cmd/cgo/ast.go
index 580a72a958..2167e9e650 100644
--- a/src/cmd/cgo/ast.go
+++ b/src/cmd/cgo/ast.go
@@ -16,59 +16,8 @@ import (
 	"strings"
 )
 
-// A Cref refers to an expression of the form C.xxx in the AST.
-type Cref struct {
-	Name     string
-	Expr     *ast.Expr
-	Context  string // "type", "expr", "const", or "call"
-	TypeName bool   // whether xxx is a C type name
-	Type     *Type  // the type of xxx
-	FuncType *FuncType
-}
-
-// A ExpFunc is an exported function, callable from C.
-type ExpFunc struct {
-	Func    *ast.FuncDecl
-	ExpName string // name to use from C
-}
-
-// A Prog collects information about a cgo program.
-type Prog struct {
-	AST         *ast.File // parsed AST
-	Preamble    string    // C preamble (doc comment on import "C")
-	PackagePath string
-	Package     string
-	Crefs       []*Cref
-	Typedef     map[string]ast.Expr
-	Vardef      map[string]*Type
-	Funcdef     map[string]*FuncType
-	Enumdef     map[string]int64
-	Constdef    map[string]string
-	ExpFuncs    []*ExpFunc
-	PtrSize     int64
-	GccOptions  []string
-	OutDefs     map[string]bool
-}
-
-// A Type collects information about a type in both the C and Go worlds.
-type Type struct {
-	Size       int64
-	Align      int64
-	C          string
-	Go         ast.Expr
-	EnumValues map[string]int64
-}
-
-// A FuncType collects information about a function type in both the C and Go worlds.
-type FuncType struct {
-	Params []*Type
-	Result *Type
-	Go     *ast.FuncType
-}
-
-func openProg(name string, p *Prog) {
-	var err os.Error
-	p.AST, err = parser.ParseFile(name, nil, nil, parser.ParseComments)
+func parse(name string, flags uint) *ast.File {
+	ast1, err := parser.ParseFile(name, nil, nil, flags)
 	if err != nil {
 		if list, ok := err.(scanner.ErrorList); ok {
 			// If err is a scanner.ErrorList, its String will print just
@@ -82,25 +31,37 @@ func openProg(name string, p *Prog) {
 		}
 		fatal("parsing %s: %s", name, err)
 	}
-	p.Package = p.AST.Name.Name()
+	return ast1
+}
+
+// ReadGo populates f with information learned from reading the
+// Go source file with the given file name.  It gathers the C preamble
+// attached to the import "C" comment, a list of references to C.xxx,
+// a list of exported functions, and the actual AST, to be rewritten and
+// printed.
+func (f *File) ReadGo(name string) {
+	// Two different parses: once with comments, once without.
+	// The printer is not good enough at printing comments in the
+	// right place when we start editing the AST behind its back,
+	// so we use ast1 to look for the doc comments on import "C"
+	// and on exported functions, and we use ast2 for translating
+	// and reprinting.
+	ast1 := parse(name, parser.ParseComments)
+	ast2 := parse(name, 0)
 
-	// Find the import "C" line and get any extra C preamble.
-	// Delete the import "C" line along the way.
+	f.Package = ast1.Name.Name()
+	f.Name = make(map[string]*Name)
+
+	// In ast1, find the import "C" line and get any extra C preamble.
 	sawC := false
-	w := 0
-	for _, decl := range p.AST.Decls {
+	for _, decl := range ast1.Decls {
 		d, ok := decl.(*ast.GenDecl)
 		if !ok {
-			p.AST.Decls[w] = decl
-			w++
 			continue
 		}
-		ws := 0
 		for _, spec := range d.Specs {
 			s, ok := spec.(*ast.ImportSpec)
 			if !ok || string(s.Path.Value) != `"C"` {
-				d.Specs[ws] = spec
-				ws++
 				continue
 			}
 			sawC = true
@@ -108,269 +69,343 @@ func openProg(name string, p *Prog) {
 				error(s.Path.Pos(), `cannot rename import "C"`)
 			}
 			if s.Doc != nil {
-				p.Preamble += doc.CommentText(s.Doc) + "\n"
+				f.Preamble += doc.CommentText(s.Doc) + "\n"
 			} else if len(d.Specs) == 1 && d.Doc != nil {
-				p.Preamble += doc.CommentText(d.Doc) + "\n"
+				f.Preamble += doc.CommentText(d.Doc) + "\n"
+			}
+		}
+	}
+	if !sawC {
+		error(noPos, `cannot find import "C"`)
+	}
+
+	// In ast2, strip the import "C" line.
+	w := 0
+	for _, decl := range ast2.Decls {
+		d, ok := decl.(*ast.GenDecl)
+		if !ok {
+			ast2.Decls[w] = decl
+			w++
+			continue
+		}
+		ws := 0
+		for _, spec := range d.Specs {
+			s, ok := spec.(*ast.ImportSpec)
+			if !ok || string(s.Path.Value) != `"C"` {
+				d.Specs[ws] = spec
+				ws++
 			}
 		}
 		if ws == 0 {
 			continue
 		}
 		d.Specs = d.Specs[0:ws]
-		p.AST.Decls[w] = d
+		ast2.Decls[w] = d
 		w++
 	}
-	p.AST.Decls = p.AST.Decls[0:w]
-
-	if !sawC {
-		error(noPos, `cannot find import "C"`)
-	}
+	ast2.Decls = ast2.Decls[0:w]
 
 	// Accumulate pointers to uses of C.x.
-	if p.Crefs == nil {
-		p.Crefs = make([]*Cref, 0, 8)
+	if f.Ref == nil {
+		f.Ref = make([]*Ref, 0, 8)
 	}
-	walk(p.AST, p, "prog")
+	f.walk(ast2, "prog", (*File).saveRef)
+
+	// Accumulate exported functions.
+	// The comments are only on ast1 but we need to
+	// save the function bodies from ast2.
+	// The first walk fills in ExpFunc, and the
+	// second walk changes the entries to
+	// refer to ast2 instead.
+	f.walk(ast1, "prog", (*File).saveExport)
+	f.walk(ast2, "prog", (*File).saveExport2)
+
+	f.AST = ast2
 }
 
-func walk(x interface{}, p *Prog, context string) {
-	switch n := x.(type) {
-	case *ast.Expr:
-		if sel, ok := (*n).(*ast.SelectorExpr); ok {
-			// For now, assume that the only instance of capital C is
-			// when used as the imported package identifier.
-			// The parser should take care of scoping in the future,
-			// so that we will be able to distinguish a "top-level C"
-			// from a local C.
-			if l, ok := sel.X.(*ast.Ident); ok && l.Name() == "C" {
-				i := len(p.Crefs)
-				if i >= cap(p.Crefs) {
-					new := make([]*Cref, 2*i)
-					for j, v := range p.Crefs {
-						new[j] = v
-					}
-					p.Crefs = new
+// Save references to C.xxx for later processing.
+func (f *File) saveRef(x interface{}, context string) {
+	n, ok := x.(*ast.Expr)
+	if !ok {
+		return
+	}
+	if sel, ok := (*n).(*ast.SelectorExpr); ok {
+		// For now, assume that the only instance of capital C is
+		// when used as the imported package identifier.
+		// The parser should take care of scoping in the future,
+		// so that we will be able to distinguish a "top-level C"
+		// from a local C.
+		if l, ok := sel.X.(*ast.Ident); ok && l.Name() == "C" {
+			i := len(f.Ref)
+			if i >= cap(f.Ref) {
+				new := make([]*Ref, 2*i)
+				for j, v := range f.Ref {
+					new[j] = v
 				}
-				p.Crefs = p.Crefs[0 : i+1]
-				p.Crefs[i] = &Cref{
-					Name:    sel.Sel.Name(),
-					Expr:    n,
-					Context: context,
+				f.Ref = new
+			}
+			if context == "as2" {
+				context = "expr"
+			}
+			goname := sel.Sel.Name()
+			name := f.Name[goname]
+			if name == nil {
+				name = &Name{
+					Go: goname,
 				}
-				break
+				f.Name[goname] = name
+			}
+			f.Ref = f.Ref[0 : i+1]
+			f.Ref[i] = &Ref{
+				Name:    name,
+				Expr:    n,
+				Context: context,
 			}
+			return
 		}
-		walk(*n, p, context)
+	}
+}
+
+// If a function should be exported add it to ExpFunc.
+func (f *File) saveExport(x interface{}, context string) {
+	n, ok := x.(*ast.FuncDecl)
+	if !ok {
+		return
+	}
+
+	if n.Doc == nil {
+		return
+	}
+	for _, c := range n.Doc.List {
+		if string(c.Text[0:9]) != "//export " {
+			continue
+		}
+
+		name := strings.TrimSpace(string(c.Text[9:]))
+		if name == "" {
+			error(c.Position, "export missing name")
+		}
+
+		if f.ExpFunc == nil {
+			f.ExpFunc = make([]*ExpFunc, 0, 8)
+		}
+		i := len(f.ExpFunc)
+		if i >= cap(f.ExpFunc) {
+			new := make([]*ExpFunc, i, 2*i)
+			copy(new, f.ExpFunc)
+			f.ExpFunc = new
+		}
+		f.ExpFunc = f.ExpFunc[0 : i+1]
+		f.ExpFunc[i] = &ExpFunc{
+			Func:    n,
+			ExpName: name,
+		}
+		break
+	}
+}
+
+// Make f.ExpFunc[i] point at the Func from this AST instead of the other one.
+func (f *File) saveExport2(x interface{}, context string) {
+	n, ok := x.(*ast.FuncDecl)
+	if !ok {
+		return
+	}
+
+	for _, exp := range f.ExpFunc {
+		if exp.Func.Name.Name() == n.Name.Name() {
+			exp.Func = n
+			break
+		}
+	}
+}
+
+// walk walks the AST x, calling visit(f, x, context) for each node.
+func (f *File) walk(x interface{}, context string, visit func(*File, interface{}, string)) {
+	visit(f, x, context)
+	switch n := x.(type) {
+	case *ast.Expr:
+		f.walk(*n, context, visit)
 
 	// everything else just recurs
 	default:
-		error(noPos, "unexpected type %T in walk", x)
+		error(noPos, "unexpected type %T in walk", x, visit)
 		panic("unexpected type")
 
 	case nil:
 
 	// These are ordered and grouped to match ../../pkg/go/ast/ast.go
 	case *ast.Field:
-		walk(&n.Type, p, "type")
+		f.walk(&n.Type, "type", visit)
 	case *ast.FieldList:
-		for _, f := range n.List {
-			walk(f, p, context)
+		for _, field := range n.List {
+			f.walk(field, context, visit)
 		}
 	case *ast.BadExpr:
 	case *ast.Ident:
 	case *ast.Ellipsis:
 	case *ast.BasicLit:
 	case *ast.FuncLit:
-		walk(n.Type, p, "type")
-		walk(n.Body, p, "stmt")
+		f.walk(n.Type, "type", visit)
+		f.walk(n.Body, "stmt", visit)
 	case *ast.CompositeLit:
-		walk(&n.Type, p, "type")
-		walk(n.Elts, p, "expr")
+		f.walk(&n.Type, "type", visit)
+		f.walk(n.Elts, "expr", visit)
 	case *ast.ParenExpr:
-		walk(&n.X, p, context)
+		f.walk(&n.X, context, visit)
 	case *ast.SelectorExpr:
-		walk(&n.X, p, "selector")
+		f.walk(&n.X, "selector", visit)
 	case *ast.IndexExpr:
-		walk(&n.X, p, "expr")
-		walk(&n.Index, p, "expr")
+		f.walk(&n.X, "expr", visit)
+		f.walk(&n.Index, "expr", visit)
 	case *ast.SliceExpr:
-		walk(&n.X, p, "expr")
-		walk(&n.Index, p, "expr")
+		f.walk(&n.X, "expr", visit)
+		f.walk(&n.Index, "expr", visit)
 		if n.End != nil {
-			walk(&n.End, p, "expr")
+			f.walk(&n.End, "expr", visit)
 		}
 	case *ast.TypeAssertExpr:
-		walk(&n.X, p, "expr")
-		walk(&n.Type, p, "type")
+		f.walk(&n.X, "expr", visit)
+		f.walk(&n.Type, "type", visit)
 	case *ast.CallExpr:
-		walk(&n.Fun, p, "call")
-		walk(n.Args, p, "expr")
+		if context == "as2" {
+			f.walk(&n.Fun, "call2", visit)
+		} else {
+			f.walk(&n.Fun, "call", visit)
+		}
+		f.walk(n.Args, "expr", visit)
 	case *ast.StarExpr:
-		walk(&n.X, p, context)
+		f.walk(&n.X, context, visit)
 	case *ast.UnaryExpr:
-		walk(&n.X, p, "expr")
+		f.walk(&n.X, "expr", visit)
 	case *ast.BinaryExpr:
-		walk(&n.X, p, "expr")
-		walk(&n.Y, p, "expr")
+		f.walk(&n.X, "expr", visit)
+		f.walk(&n.Y, "expr", visit)
 	case *ast.KeyValueExpr:
-		walk(&n.Key, p, "expr")
-		walk(&n.Value, p, "expr")
+		f.walk(&n.Key, "expr", visit)
+		f.walk(&n.Value, "expr", visit)
 
 	case *ast.ArrayType:
-		walk(&n.Len, p, "expr")
-		walk(&n.Elt, p, "type")
+		f.walk(&n.Len, "expr", visit)
+		f.walk(&n.Elt, "type", visit)
 	case *ast.StructType:
-		walk(n.Fields, p, "field")
+		f.walk(n.Fields, "field", visit)
 	case *ast.FuncType:
-		walk(n.Params, p, "field")
+		f.walk(n.Params, "field", visit)
 		if n.Results != nil {
-			walk(n.Results, p, "field")
+			f.walk(n.Results, "field", visit)
 		}
 	case *ast.InterfaceType:
-		walk(n.Methods, p, "field")
+		f.walk(n.Methods, "field", visit)
 	case *ast.MapType:
-		walk(&n.Key, p, "type")
-		walk(&n.Value, p, "type")
+		f.walk(&n.Key, "type", visit)
+		f.walk(&n.Value, "type", visit)
 	case *ast.ChanType:
-		walk(&n.Value, p, "type")
+		f.walk(&n.Value, "type", visit)
 
 	case *ast.BadStmt:
 	case *ast.DeclStmt:
-		walk(n.Decl, p, "decl")
+		f.walk(n.Decl, "decl", visit)
 	case *ast.EmptyStmt:
 	case *ast.LabeledStmt:
-		walk(n.Stmt, p, "stmt")
+		f.walk(n.Stmt, "stmt", visit)
 	case *ast.ExprStmt:
-		walk(&n.X, p, "expr")
+		f.walk(&n.X, "expr", visit)
 	case *ast.IncDecStmt:
-		walk(&n.X, p, "expr")
+		f.walk(&n.X, "expr", visit)
 	case *ast.AssignStmt:
-		walk(n.Lhs, p, "expr")
-		walk(n.Rhs, p, "expr")
+		f.walk(n.Lhs, "expr", visit)
+		if len(n.Lhs) == 2 {
+			f.walk(n.Rhs, "as2", visit)
+		} else {
+			f.walk(n.Rhs, "expr", visit)
+		}
 	case *ast.GoStmt:
-		walk(n.Call, p, "expr")
+		f.walk(n.Call, "expr", visit)
 	case *ast.DeferStmt:
-		walk(n.Call, p, "expr")
+		f.walk(n.Call, "expr", visit)
 	case *ast.ReturnStmt:
-		walk(n.Results, p, "expr")
+		f.walk(n.Results, "expr", visit)
 	case *ast.BranchStmt:
 	case *ast.BlockStmt:
-		walk(n.List, p, "stmt")
+		f.walk(n.List, "stmt", visit)
 	case *ast.IfStmt:
-		walk(n.Init, p, "stmt")
-		walk(&n.Cond, p, "expr")
-		walk(n.Body, p, "stmt")
-		walk(n.Else, p, "stmt")
+		f.walk(n.Init, "stmt", visit)
+		f.walk(&n.Cond, "expr", visit)
+		f.walk(n.Body, "stmt", visit)
+		f.walk(n.Else, "stmt", visit)
 	case *ast.CaseClause:
-		walk(n.Values, p, "expr")
-		walk(n.Body, p, "stmt")
+		f.walk(n.Values, "expr", visit)
+		f.walk(n.Body, "stmt", visit)
 	case *ast.SwitchStmt:
-		walk(n.Init, p, "stmt")
-		walk(&n.Tag, p, "expr")
-		walk(n.Body, p, "stmt")
+		f.walk(n.Init, "stmt", visit)
+		f.walk(&n.Tag, "expr", visit)
+		f.walk(n.Body, "stmt", visit)
 	case *ast.TypeCaseClause:
-		walk(n.Types, p, "type")
-		walk(n.Body, p, "stmt")
+		f.walk(n.Types, "type", visit)
+		f.walk(n.Body, "stmt", visit)
 	case *ast.TypeSwitchStmt:
-		walk(n.Init, p, "stmt")
-		walk(n.Assign, p, "stmt")
-		walk(n.Body, p, "stmt")
+		f.walk(n.Init, "stmt", visit)
+		f.walk(n.Assign, "stmt", visit)
+		f.walk(n.Body, "stmt", visit)
 	case *ast.CommClause:
-		walk(n.Lhs, p, "expr")
-		walk(n.Rhs, p, "expr")
-		walk(n.Body, p, "stmt")
+		f.walk(n.Lhs, "expr", visit)
+		f.walk(n.Rhs, "expr", visit)
+		f.walk(n.Body, "stmt", visit)
 	case *ast.SelectStmt:
-		walk(n.Body, p, "stmt")
+		f.walk(n.Body, "stmt", visit)
 	case *ast.ForStmt:
-		walk(n.Init, p, "stmt")
-		walk(&n.Cond, p, "expr")
-		walk(n.Post, p, "stmt")
-		walk(n.Body, p, "stmt")
+		f.walk(n.Init, "stmt", visit)
+		f.walk(&n.Cond, "expr", visit)
+		f.walk(n.Post, "stmt", visit)
+		f.walk(n.Body, "stmt", visit)
 	case *ast.RangeStmt:
-		walk(&n.Key, p, "expr")
-		walk(&n.Value, p, "expr")
-		walk(&n.X, p, "expr")
-		walk(n.Body, p, "stmt")
+		f.walk(&n.Key, "expr", visit)
+		f.walk(&n.Value, "expr", visit)
+		f.walk(&n.X, "expr", visit)
+		f.walk(n.Body, "stmt", visit)
 
 	case *ast.ImportSpec:
 	case *ast.ValueSpec:
-		walk(&n.Type, p, "type")
-		walk(n.Values, p, "expr")
+		f.walk(&n.Type, "type", visit)
+		f.walk(n.Values, "expr", visit)
 	case *ast.TypeSpec:
-		walk(&n.Type, p, "type")
+		f.walk(&n.Type, "type", visit)
 
 	case *ast.BadDecl:
 	case *ast.GenDecl:
-		walk(n.Specs, p, "spec")
+		f.walk(n.Specs, "spec", visit)
 	case *ast.FuncDecl:
 		if n.Recv != nil {
-			walk(n.Recv, p, "field")
+			f.walk(n.Recv, "field", visit)
 		}
-		walk(n.Type, p, "type")
+		f.walk(n.Type, "type", visit)
 		if n.Body != nil {
-			walk(n.Body, p, "stmt")
+			f.walk(n.Body, "stmt", visit)
 		}
 
-		checkExpFunc(n, p)
-
 	case *ast.File:
-		walk(n.Decls, p, "decl")
+		f.walk(n.Decls, "decl", visit)
 
 	case *ast.Package:
-		for _, f := range n.Files {
-			walk(f, p, "file")
+		for _, file := range n.Files {
+			f.walk(file, "file", visit)
 		}
 
 	case []ast.Decl:
 		for _, d := range n {
-			walk(d, p, context)
+			f.walk(d, context, visit)
 		}
 	case []ast.Expr:
 		for i := range n {
-			walk(&n[i], p, context)
+			f.walk(&n[i], context, visit)
 		}
 	case []ast.Stmt:
 		for _, s := range n {
-			walk(s, p, context)
+			f.walk(s, context, visit)
 		}
 	case []ast.Spec:
 		for _, s := range n {
-			walk(s, p, context)
-		}
-	}
-}
-
-// If a function should be exported add it to ExpFuncs.
-func checkExpFunc(n *ast.FuncDecl, p *Prog) {
-	if n.Doc == nil {
-		return
-	}
-	for _, c := range n.Doc.List {
-		if string(c.Text[0:9]) != "//export " {
-			continue
-		}
-
-		name := strings.TrimSpace(string(c.Text[9:]))
-		if name == "" {
-			error(c.Position, "export missing name")
-		}
-
-		if p.ExpFuncs == nil {
-			p.ExpFuncs = make([]*ExpFunc, 0, 8)
-		}
-		i := len(p.ExpFuncs)
-		if i >= cap(p.ExpFuncs) {
-			new := make([]*ExpFunc, 2*i)
-			for j, v := range p.ExpFuncs {
-				new[j] = v
-			}
-			p.ExpFuncs = new
+			f.walk(s, context, visit)
 		}
-		p.ExpFuncs = p.ExpFuncs[0 : i+1]
-		p.ExpFuncs[i] = &ExpFunc{
-			Func:    n,
-			ExpName: name,
-		}
-		break
 	}
 }
diff --git a/src/cmd/cgo/doc.go b/src/cmd/cgo/doc.go
index 022a87c154..dce8e86828 100644
--- a/src/cmd/cgo/doc.go
+++ b/src/cmd/cgo/doc.go
@@ -23,6 +23,19 @@ the package.  For example:
 	// #include <errno.h>
 	import "C"
 
+C identifiers or field names that are keywords in Go can be
+accessed by prefixing them with an underscore: if x points at
+a C struct with a field named "type", x._type accesses the field.
+
+To access a struct, union, or enum type directly, prefix it with
+struct_, union_, or enum_, as in C.struct_stat.
+
+Any C function that returns a value may be called in a multiple
+assignment context to retrieve both the return value and the
+C errno variable as an os.Error.  For example:
+
+	n, err := C.atoi("abc")
+
 Cgo transforms the input file into four output files: two Go source
 files, a C file for 6c (or 8c or 5c), and a C file for gcc.
 
diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go
index 5e12a66877..7638e32d85 100644
--- a/src/cmd/cgo/gcc.go
+++ b/src/cmd/cgo/gcc.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Annotate Crefs in Prog with C types by parsing gcc debug output.
+// Annotate Ref in Prog with C types by parsing gcc debug output.
 // Conversion of debug output to Go types.
 
 package main
@@ -12,6 +12,7 @@ import (
 	"debug/dwarf"
 	"debug/elf"
 	"debug/macho"
+	"flag"
 	"fmt"
 	"go/ast"
 	"go/parser"
@@ -21,12 +22,64 @@ import (
 	"strings"
 )
 
-func (p *Prog) loadDebugInfo() {
+var debugDefine = flag.Bool("debug-define", false, "print relevant #defines")
+var debugGcc = flag.Bool("debug-gcc", false, "print gcc invocations")
+
+var nameToC = map[string]string{
+	"schar":     "signed char",
+	"uchar":     "unsigned char",
+	"ushort":    "unsigned short",
+	"uint":      "unsigned int",
+	"ulong":     "unsigned long",
+	"longlong":  "long long",
+	"ulonglong": "unsigned long long",
+}
+
+// cname returns the C name to use for C.s.
+// The expansions are listed in nameToC and also
+// struct_foo becomes "struct foo", and similarly for
+// union and enum.
+func cname(s string) string {
+	if t, ok := nameToC[s]; ok {
+		return t
+	}
+
+	if strings.HasPrefix(s, "struct_") {
+		return "struct " + s[len("struct_"):]
+	}
+	if strings.HasPrefix(s, "union_") {
+		return "union " + s[len("union_"):]
+	}
+	if strings.HasPrefix(s, "enum_") {
+		return "enum " + s[len("enum_"):]
+	}
+	return s
+}
+
+// Translate rewrites f.AST, the original Go input, to remove
+// references to the imported package C, replacing them with
+// references to the equivalent Go types, functions, and variables.
+func (p *Package) Translate(f *File) {
+	for _, cref := range f.Ref {
+		// Convert C.ulong to C.unsigned long, etc.
+		cref.Name.C = cname(cref.Name.Go)
+	}
+	p.loadDefines(f)
+	needType := p.guessKinds(f)
+	if len(needType) > 0 {
+		p.loadDWARF(f, needType)
+	}
+	p.rewriteRef(f)
+}
+
+// loadDefines coerces gcc into spitting out the #defines in use
+// in the file f and saves relevant renamings in f.Name[name].Define.
+func (p *Package) loadDefines(f *File) {
 	var b bytes.Buffer
+	b.WriteString(builtinProlog)
+	b.WriteString(f.Preamble)
+	stdout := p.gccDefines(b.Bytes())
 
-	b.WriteString(p.Preamble)
-	stdout := p.gccPostProc(b.Bytes())
-	defines := make(map[string]string)
 	for _, line := range strings.Split(stdout, "\n", -1) {
 		if len(line) < 9 || line[0:7] != "#define" {
 			continue
@@ -48,68 +101,107 @@ func (p *Prog) loadDebugInfo() {
 			val = strings.TrimSpace(line[tabIndex:])
 		}
 
-		// Only allow string, character, and numeric constants. Ignoring #defines for
-		// symbols allows those symbols to be referenced in Go, as they will be
-		// translated by gcc later.
-		_, err := strconv.Atoi(string(val[0]))
-		if err == nil || val[0] == '\'' || val[0] == '"' {
-			defines[key] = val
-		}
-	}
-
-	// Construct a slice of unique names from p.Crefs.
-	m := make(map[string]int)
-	for _, c := range p.Crefs {
-		// If we've already found this name as a define, it is not a Cref.
-		if val, ok := defines[c.Name]; ok {
-			_, err := parser.ParseExpr("", val, nil)
-			if err != nil {
-				fmt.Fprintf(os.Stderr, "The value in C.%s does not parse as a Go expression; cannot use.\n", c.Name)
-				os.Exit(2)
+		if n := f.Name[key]; n != nil {
+			if *debugDefine {
+				fmt.Fprintf(os.Stderr, "#define %s %s\n", key, val)
 			}
-
-			c.Context = "const"
-			c.TypeName = false
-			p.Constdef[c.Name] = val
-			continue
+			n.Define = val
 		}
-		m[c.Name] = -1
-	}
-	names := make([]string, 0, len(m))
-	for name, _ := range m {
-		i := len(names)
-		names = names[0 : i+1]
-		names[i] = name
-		m[name] = i
 	}
+}
 
+// guessKinds tricks gcc into revealing the kind of each
+// name xxx for the references C.xxx in the Go input.
+// The kind is either a constant, type, or variable.
+func (p *Package) guessKinds(f *File) []*Name {
 	// Coerce gcc into telling us whether each name is
 	// a type, a value, or undeclared.  We compile a function
 	// containing the line:
 	//	name;
 	// If name is a type, gcc will print:
-	//	x.c:2: warning: useless type name in empty declaration
+	//	cgo-test:2: warning: useless type name in empty declaration
 	// If name is a value, gcc will print
-	//	x.c:2: warning: statement with no effect
+	//	cgo-test:2: warning: statement with no effect
 	// If name is undeclared, gcc will print
-	//	x.c:2: error: 'name' undeclared (first use in this function)
+	//	cgo-test:2: error: 'name' undeclared (first use in this function)
 	// A line number directive causes the line number to
 	// correspond to the index in the names array.
-	b.Reset()
-	b.WriteString(p.Preamble)
+	//
+	// The line also has an enum declaration:
+	//	name; enum { _cgo_enum_1 = name };
+	// If name is not a constant, gcc will print:
+	//	cgo-test:4: error: enumerator value for '_cgo_enum_4' is not an integer constant
+	// we assume lines without that error are constants.
+
+	// Make list of names that need sniffing, type lookup.
+	toSniff := make([]*Name, 0, len(f.Name))
+	needType := make([]*Name, 0, len(f.Name))
+
+	for _, n := range f.Name {
+		// If we've already found this name as a #define
+		// and we can translate it as a constant value, do so.
+		if n.Define != "" {
+			ok := false
+			if _, err := strconv.Atoi(n.Define); err == nil {
+				ok = true
+			} else if n.Define[0] == '"' || n.Define[0] == '\'' {
+				_, err := parser.ParseExpr("", n.Define, nil)
+				if err == nil {
+					ok = true
+				}
+			}
+			if ok {
+				n.Kind = "const"
+				n.Const = n.Define
+				continue
+			}
+
+			if isName(n.Define) {
+				n.C = n.Define
+			}
+		}
+
+		// If this is a struct, union, or enum type name,
+		// record the kind but also that we need type information.
+		if strings.HasPrefix(n.C, "struct ") || strings.HasPrefix(n.C, "union ") || strings.HasPrefix(n.C, "enum ") {
+			n.Kind = "type"
+			i := len(needType)
+			needType = needType[0 : i+1]
+			needType[i] = n
+			continue
+		}
+
+		i := len(toSniff)
+		toSniff = toSniff[0 : i+1]
+		toSniff[i] = n
+	}
+
+	if len(toSniff) == 0 {
+		return needType
+	}
+
+	var b bytes.Buffer
+	b.WriteString(builtinProlog)
+	b.WriteString(f.Preamble)
 	b.WriteString("void f(void) {\n")
 	b.WriteString("#line 0 \"cgo-test\"\n")
-	for _, n := range names {
-		b.WriteString(n)
-		b.WriteString(";\n")
+	for i, n := range toSniff {
+		fmt.Fprintf(&b, "%s; enum { _cgo_enum_%d = %s }; /* cgo-test:%d */\n", n.C, i, n.C, i)
 	}
 	b.WriteString("}\n")
-
-	kind := make(map[string]string)
-	_, stderr := p.gccDebug(b.Bytes())
+	stderr := p.gccErrors(b.Bytes())
 	if stderr == "" {
-		fatal("gcc produced no output")
+		fatal("gcc produced no output\non input:\n%s", b.Bytes())
+	}
+
+	names := make([]*Name, len(toSniff))
+	copy(names, toSniff)
+
+	isConst := make([]bool, len(toSniff))
+	for i := range isConst {
+		isConst[i] = true // until proven otherwise
 	}
+
 	for _, line := range strings.Split(stderr, "\n", -1) {
 		if len(line) < 9 || line[0:9] != "cgo-test:" {
 			continue
@@ -129,26 +221,50 @@ func (p *Prog) loadDebugInfo() {
 			continue
 		case strings.Index(line, ": useless type name in empty declaration") >= 0:
 			what = "type"
+			isConst[i] = false
 		case strings.Index(line, ": statement with no effect") >= 0:
-			what = "value"
+			what = "not-type" // const or func or var
 		case strings.Index(line, "undeclared") >= 0:
-			what = "error"
+			error(noPos, "%s", strings.TrimSpace(line[colon+1:]))
+		case strings.Index(line, "is not an integer constant") >= 0:
+			isConst[i] = false
+			continue
 		}
-		if old, ok := kind[names[i]]; ok && old != what {
-			error(noPos, "inconsistent gcc output about C.%s", names[i])
+		n := toSniff[i]
+		if n == nil {
+			continue
 		}
-		kind[names[i]] = what
+		toSniff[i] = nil
+		n.Kind = what
+
+		j := len(needType)
+		needType = needType[0 : j+1]
+		needType[j] = n
 	}
-	for _, n := range names {
-		if _, ok := kind[n]; !ok {
-			error(noPos, "could not determine kind of name for C.%s", n)
+	for i, b := range isConst {
+		if b {
+			names[i].Kind = "const"
 		}
 	}
-
+	for _, n := range toSniff {
+		if n == nil {
+			continue
+		}
+		if n.Kind != "" {
+			continue
+		}
+		error(noPos, "could not determine kind of name for C.%s", n.Go)
+	}
 	if nerrors > 0 {
-		fatal("failed to interpret gcc output:\n%s", stderr)
+		fatal("unresolved names")
 	}
+	return needType
+}
 
+// loadDWARF parses the DWARF debug information generated
+// by gcc to learn the details of the constants, variables, and types
+// being referred to as C.xxx.
+func (p *Package) loadDWARF(f *File, names []*Name) {
 	// Extract the types from the DWARF section of an object
 	// from a well-formed C program.  Gcc only generates DWARF info
 	// for symbols in the object file, so it is not enough to print the
@@ -157,19 +273,24 @@ func (p *Prog) loadDebugInfo() {
 	//	typeof(names[i]) *__cgo__i;
 	// for each entry in names and then dereference the type we
 	// learn for __cgo__i.
-	b.Reset()
-	b.WriteString(p.Preamble)
+	var b bytes.Buffer
+	b.WriteString(builtinProlog)
+	b.WriteString(f.Preamble)
 	for i, n := range names {
-		fmt.Fprintf(&b, "typeof(%s) *__cgo__%d;\n", n, i)
-	}
-	d, stderr := p.gccDebug(b.Bytes())
-	if d == nil {
-		fatal("gcc failed:\n%s\non input:\n%s", stderr, b.Bytes())
+		fmt.Fprintf(&b, "typeof(%s) *__cgo__%d;\n", n.C, i)
+		if n.Kind == "const" {
+			fmt.Fprintf(&b, "enum { __cgo_enum__%d = %s };\n", i, n.C)
+		}
 	}
+	d := p.gccDebug(b.Bytes())
 
 	// Scan DWARF info for top-level TagVariable entries with AttrName __cgo__i.
 	types := make([]dwarf.Type, len(names))
 	enums := make([]dwarf.Offset, len(names))
+	nameToIndex := make(map[*Name]int)
+	for i, n := range names {
+		nameToIndex[n] = i
+	}
 	r := d.Reader()
 	for {
 		e, err := r.Next()
@@ -192,9 +313,11 @@ func (p *Prog) loadDebugInfo() {
 				}
 				if e.Tag == dwarf.TagEnumerator {
 					entryName := e.Val(dwarf.AttrName).(string)
-					i, ok := m[entryName]
-					if ok {
-						enums[i] = offset
+					if strings.HasPrefix(entryName, "__cgo_enum__") {
+						n, _ := strconv.Atoi(entryName[len("__cgo_enum__"):])
+						if 0 <= n && n < len(names) {
+							enums[n] = offset
+						}
 					}
 				}
 			}
@@ -234,97 +357,205 @@ func (p *Prog) loadDebugInfo() {
 		}
 	}
 
-	// Record types and typedef information in Crefs.
+	// Record types and typedef information.
 	var conv typeConv
 	conv.Init(p.PtrSize)
-	for _, c := range p.Crefs {
-		i, ok := m[c.Name]
-		if !ok {
-			if _, ok := p.Constdef[c.Name]; !ok {
-				fatal("Cref %s is no longer around", c.Name)
-			}
-			continue
-		}
-		c.TypeName = kind[c.Name] == "type"
+	for i, n := range names {
 		f, fok := types[i].(*dwarf.FuncType)
-		if c.Context == "call" && !c.TypeName && fok {
-			c.FuncType = conv.FuncType(f)
+		if n.Kind != "type" && fok {
+			n.Kind = "func"
+			n.FuncType = conv.FuncType(f)
 		} else {
-			c.Type = conv.Type(types[i])
+			n.Type = conv.Type(types[i])
+			if enums[i] != 0 && n.Type.EnumValues != nil {
+				n.Kind = "const"
+				n.Const = strconv.Itoa64(n.Type.EnumValues[fmt.Sprintf("__cgo_enum__%d", i)])
+			}
 		}
 	}
-	p.Typedef = conv.typedef
+	f.Typedef = conv.typedef
 }
 
-func concat(a, b []string) []string {
-	c := make([]string, len(a)+len(b))
-	for i, s := range a {
-		c[i] = s
+// rewriteRef rewrites all the C.xxx references in f.AST to refer to the
+// Go equivalents, now that we have figured out the meaning of all
+// the xxx.
+func (p *Package) rewriteRef(f *File) {
+	// Assign mangled names.
+	for _, n := range f.Name {
+		if n.Kind == "not-type" {
+			n.Kind = "var"
+		}
+		if n.Mangle == "" {
+			n.Mangle = "_C" + n.Kind + "_" + n.Go
+		}
 	}
-	for i, s := range b {
-		c[i+len(a)] = s
+
+	// Now that we have all the name types filled in,
+	// scan through the Refs to identify the ones that
+	// are trying to do a ,err call.  Also check that
+	// functions are only used in calls.
+	for _, r := range f.Ref {
+		var expr ast.Expr = ast.NewIdent(r.Name.Mangle) // default
+		switch r.Context {
+		case "call", "call2":
+			if r.Name.Kind != "func" {
+				if r.Name.Kind == "type" {
+					r.Context = "type"
+					expr = r.Name.Type.Go
+					break
+				}
+				error(r.Pos(), "call of non-function C.%s", r.Name.Go)
+				break
+			}
+			if r.Context == "call2" {
+				if r.Name.FuncType.Result == nil {
+					error(r.Pos(), "assignment count mismatch: 2 = 0")
+				}
+				// Invent new Name for the two-result function.
+				n := f.Name["2"+r.Name.Go]
+				if n == nil {
+					n = new(Name)
+					*n = *r.Name
+					n.AddError = true
+					n.Mangle = "_C2func_" + n.Go
+					f.Name["2"+r.Name.Go] = n
+					expr = ast.NewIdent(n.Mangle)
+				}
+				r.Name = n
+				break
+			}
+		case "expr":
+			if r.Name.Kind == "func" {
+				error(r.Pos(), "must call C.%s", r.Name.Go)
+			}
+			if r.Name.Kind == "type" {
+				// Okay - might be new(T)
+				expr = r.Name.Type.Go
+			}
+			if r.Name.Kind == "var" {
+				expr = &ast.StarExpr{X: expr}
+			}
+
+		case "type":
+			if r.Name.Kind != "type" {
+				error(r.Pos(), "expression C.%s used as type", r.Name.Go)
+			}
+			expr = r.Name.Type.Go
+		default:
+			if r.Name.Kind == "func" {
+				error(r.Pos(), "must call C.%s", r.Name.Go)
+			}
+		}
+		*r.Expr = expr
 	}
-	return c
 }
 
-// gccDebug runs gcc -gdwarf-2 over the C program stdin and
-// returns the corresponding DWARF data and any messages
-// printed to standard error.
-func (p *Prog) gccDebug(stdin []byte) (*dwarf.Data, string) {
-	machine := "-m32"
+// gccMachine returns the gcc -m flag to use, either "-m32" or "-m64".
+func (p *Package) gccMachine() string {
 	if p.PtrSize == 8 {
-		machine = "-m64"
+		return "-m64"
 	}
+	return "-m32"
+}
 
-	tmp := "_cgo_.o"
-	base := []string{
+const gccTmp = "_cgo_.o"
+
+// gccCmd returns the gcc command line to use for compiling
+// the input.
+func (p *Package) gccCmd() []string {
+	return []string{
 		"gcc",
-		machine,
+		p.gccMachine(),
 		"-Wall",                             // many warnings
 		"-Werror",                           // warnings are errors
-		"-o" + tmp,                          // write object to tmp
+		"-o" + gccTmp,                       // write object to tmp
 		"-gdwarf-2",                         // generate DWARF v2 debugging symbols
 		"-fno-eliminate-unused-debug-types", // gets rid of e.g. untyped enum otherwise
 		"-c",                                // do not link
 		"-xc",                               // input language is C
 		"-",                                 // read input from standard input
 	}
-	_, stderr, ok := run(stdin, concat(base, p.GccOptions))
-	if !ok {
-		return nil, string(stderr)
-	}
+}
+
+// gccDebug runs gcc -gdwarf-2 over the C program stdin and
+// returns the corresponding DWARF data and any messages
+// printed to standard error.
+func (p *Package) gccDebug(stdin []byte) *dwarf.Data {
+	runGcc(stdin, concat(p.gccCmd(), p.GccOptions))
 
 	// Try to parse f as ELF and Mach-O and hope one works.
 	var f interface {
 		DWARF() (*dwarf.Data, os.Error)
 	}
 	var err os.Error
-	if f, err = elf.Open(tmp); err != nil {
-		if f, err = macho.Open(tmp); err != nil {
-			fatal("cannot parse gcc output %s as ELF or Mach-O object", tmp)
+	if f, err = elf.Open(gccTmp); err != nil {
+		if f, err = macho.Open(gccTmp); err != nil {
+			fatal("cannot parse gcc output %s as ELF or Mach-O object", gccTmp)
 		}
 	}
 
 	d, err := f.DWARF()
 	if err != nil {
-		fatal("cannot load DWARF debug information from %s: %s", tmp, err)
+		fatal("cannot load DWARF debug information from %s: %s", gccTmp, err)
 	}
-	return d, ""
+	return d
 }
 
-func (p *Prog) gccPostProc(stdin []byte) string {
-	machine := "-m32"
-	if p.PtrSize == 8 {
-		machine = "-m64"
+// gccDefines runs gcc -E -dM -xc - over the C program stdin
+// and returns the corresponding standard output, which is the
+// #defines that gcc encountered while processing the input
+// and its included files.
+func (p *Package) gccDefines(stdin []byte) string {
+	base := []string{"gcc", p.gccMachine(), "-E", "-dM", "-xc", "-"}
+	stdout, _ := runGcc(stdin, concat(base, p.GccOptions))
+	return stdout
+}
+
+// gccErrors runs gcc over the C program stdin and returns
+// the errors that gcc prints.  That is, this function expects
+// gcc to fail.
+func (p *Package) gccErrors(stdin []byte) string {
+	// TODO(rsc): require failure
+	args := concat(p.gccCmd(), p.GccOptions)
+	if *debugGcc {
+		fmt.Fprintf(os.Stderr, "$ %s <<EOF\n", strings.Join(args, " "))
+		os.Stderr.Write(stdin)
+		fmt.Fprint(os.Stderr, "EOF\n")
+	}
+	stdout, stderr, _ := run(stdin, args)
+	if *debugGcc {
+		os.Stderr.Write(stdout)
+		os.Stderr.Write(stderr)
 	}
+	return string(stderr)
+}
 
-	base := []string{"gcc", machine, "-E", "-dM", "-xc", "-"}
-	stdout, stderr, ok := run(stdin, concat(base, p.GccOptions))
+// runGcc runs the gcc command line args with stdin on standard input.
+// If the command exits with a non-zero exit status, runGcc prints
+// details about what was run and exits.
+// Otherwise runGcc returns the data written to standard output and standard error.
+// Note that for some of the uses we expect useful data back
+// on standard error, but for those uses gcc must still exit 0.
+func runGcc(stdin []byte, args []string) (string, string) {
+	if *debugGcc {
+		fmt.Fprintf(os.Stderr, "$ %s <<EOF\n", strings.Join(args, " "))
+		os.Stderr.Write(stdin)
+		fmt.Fprint(os.Stderr, "EOF\n")
+	}
+	stdout, stderr, ok := run(stdin, args)
+	if *debugGcc {
+		os.Stderr.Write(stdout)
+		os.Stderr.Write(stderr)
+	}
 	if !ok {
-		return string(stderr)
+		fmt.Fprint(os.Stderr, "Error running gcc:\n")
+		fmt.Fprintf(os.Stderr, "$ %s <<EOF\n", strings.Join(args, " "))
+		os.Stderr.Write(stdin)
+		fmt.Fprint(os.Stderr, "EOF\n")
+		os.Stderr.Write(stderr)
+		os.Exit(2)
 	}
-
-	return string(stdout)
+	return string(stdout), string(stderr)
 }
 
 // A typeConv is a translator from dwarf types to Go types
@@ -388,7 +619,7 @@ func base(dt dwarf.Type) dwarf.Type {
 }
 
 // Map from dwarf text names to aliases we use in package "C".
-var cnameMap = map[string]string{
+var dwarfToName = map[string]string{
 	"long int":               "long",
 	"long unsigned int":      "ulong",
 	"unsigned int":           "uint",
@@ -415,6 +646,7 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 	t.C = dtype.Common().Name
 	t.EnumValues = nil
 	c.m[dtype] = t
+
 	if t.Size < 0 {
 		// Unsized types are [0]byte
 		t.Size = 0
@@ -555,7 +787,7 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 		} else if t.C == "" {
 			t.C = dt.Kind + " " + tag
 		}
-		name := c.Ident("_C" + dt.Kind + "_" + tag)
+		name := c.Ident("_Ctype_" + dt.Kind + "_" + tag)
 		t.Go = name // publish before recursive calls
 		switch dt.Kind {
 		case "union", "class":
@@ -583,7 +815,7 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 			t.Align = c.ptrSize
 			break
 		}
-		name := c.Ident("_C_" + dt.Name)
+		name := c.Ident("_Ctypedef_" + dt.Name)
 		t.Go = name // publish before recursive call
 		sub := c.Type(dt.Type)
 		t.Size = sub.Size
@@ -628,11 +860,11 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 	case *dwarf.AddrType, *dwarf.BoolType, *dwarf.CharType, *dwarf.IntType, *dwarf.FloatType, *dwarf.UcharType, *dwarf.UintType:
 		s := dtype.Common().Name
 		if s != "" {
-			if ss, ok := cnameMap[s]; ok {
+			if ss, ok := dwarfToName[s]; ok {
 				s = ss
 			}
 			s = strings.Join(strings.Split(s, " ", -1), "") // strip spaces
-			name := c.Ident("_C_" + s)
+			name := c.Ident("_Ctype_" + s)
 			c.typedef[name.Name()] = t.Go
 			t.Go = name
 		}
@@ -710,7 +942,9 @@ func (c *typeConv) FuncType(dtype *dwarf.FuncType) *FuncType {
 }
 
 // Identifier
-func (c *typeConv) Ident(s string) *ast.Ident { return ast.NewIdent(s) }
+func (c *typeConv) Ident(s string) *ast.Ident {
+	return ast.NewIdent(s)
+}
 
 // Opaque type of n bytes.
 func (c *typeConv) Opaque(n int64) ast.Expr {
@@ -736,13 +970,14 @@ func (c *typeConv) pad(fld []*ast.Field, size int64) []*ast.Field {
 	return fld
 }
 
-// Struct conversion
+// Struct conversion: return Go and (6g) C syntax for type.
 func (c *typeConv) Struct(dt *dwarf.StructType) (expr *ast.StructType, csyntax string, align int64) {
-	csyntax = "struct { "
+	var buf bytes.Buffer
+	buf.WriteString("struct {")
 	fld := make([]*ast.Field, 0, 2*len(dt.Field)+1) // enough for padding around every field
 	off := int64(0)
 
-	// Mangle struct fields that happen to be named Go keywords into
+	// Rename struct fields that happen to be named Go keywords into
 	// _{keyword}.  Create a map from C ident -> Go ident.  The Go ident will
 	// be mangled.  Any existing identifier that already has the same name on
 	// the C-side will cause the Go-mangled version to be prefixed with _.
@@ -783,7 +1018,10 @@ func (c *typeConv) Struct(dt *dwarf.StructType) (expr *ast.StructType, csyntax s
 
 		fld[n] = &ast.Field{Names: []*ast.Ident{c.Ident(ident[f.Name])}, Type: t.Go}
 		off += t.Size
-		csyntax += t.C + " " + f.Name + "; "
+		buf.WriteString(t.C)
+		buf.WriteString(" ")
+		buf.WriteString(f.Name)
+		buf.WriteString("; ")
 		if t.Align > align {
 			align = t.Align
 		}
@@ -795,7 +1033,8 @@ func (c *typeConv) Struct(dt *dwarf.StructType) (expr *ast.StructType, csyntax s
 	if off != dt.ByteSize {
 		fatal("struct size calculation error")
 	}
-	csyntax += "}"
+	buf.WriteString("}")
+	csyntax = buf.String()
 	expr = &ast.StructType{Fields: &ast.FieldList{List: fld}}
 	return
 }
diff --git a/src/cmd/cgo/main.go b/src/cmd/cgo/main.go
index 070146c9ac..f0c64407e8 100644
--- a/src/cmd/cgo/main.go
+++ b/src/cmd/cgo/main.go
@@ -11,13 +11,91 @@
 package main
 
 import (
+	"flag"
 	"fmt"
 	"go/ast"
+	"go/token"
 	"os"
+	"reflect"
 	"strings"
 )
 
-func usage() { fmt.Fprint(os.Stderr, "usage: cgo [compiler options] file.go ...\n") }
+// A Package collects information about the package we're going to write.
+type Package struct {
+	PackageName string // name of package
+	PackagePath string
+	PtrSize     int64
+	GccOptions  []string
+	Written     map[string]bool
+	Name        map[string]*Name    // accumulated Name from Files
+	Typedef     map[string]ast.Expr // accumulated Typedef from Files
+	ExpFunc     []*ExpFunc          // accumulated ExpFunc from Files
+	Decl        []ast.Decl
+}
+
+// A File collects information about a single Go input file.
+type File struct {
+	AST      *ast.File           // parsed AST
+	Package  string              // Package name
+	Preamble string              // C preamble (doc comment on import "C")
+	Ref      []*Ref              // all references to C.xxx in AST
+	ExpFunc  []*ExpFunc          // exported functions for this file
+	Name     map[string]*Name    // map from Go name to Name
+	Typedef  map[string]ast.Expr // translations of all necessary types from C
+}
+
+// A Ref refers to an expression of the form C.xxx in the AST.
+type Ref struct {
+	Name    *Name
+	Expr    *ast.Expr
+	Context string // "type", "expr", "call", or "call2"
+}
+
+func (r *Ref) Pos() token.Position {
+	return (*r.Expr).Pos()
+}
+
+// A Name collects information about C.xxx.
+type Name struct {
+	Go       string // name used in Go referring to package C
+	Mangle   string // name used in generated Go
+	C        string // name used in C
+	Define   string // #define expansion
+	Kind     string // "const", "type", "var", "func", "not-type"
+	Type     *Type  // the type of xxx
+	FuncType *FuncType
+	AddError bool
+	Const    string // constant definition
+}
+
+// A ExpFunc is an exported function, callable from C.
+// Such functions are identified in the Go input file
+// by doc comments containing the line //export ExpName
+type ExpFunc struct {
+	Func    *ast.FuncDecl
+	ExpName string // name to use from C
+}
+
+// A Type collects information about a type in both the C and Go worlds.
+type Type struct {
+	Size       int64
+	Align      int64
+	C          string
+	Go         ast.Expr
+	EnumValues map[string]int64
+}
+
+// A FuncType collects information about a function type in both the C and Go worlds.
+type FuncType struct {
+	Params []*Type
+	Result *Type
+	Go     *ast.FuncType
+}
+
+func usage() {
+	fmt.Fprint(os.Stderr, "usage: cgo [compiler options] file.go ...\n")
+	os.Exit(2)
+}
 
 var ptrSizeMap = map[string]int64{
 	"386":   4,
@@ -25,43 +103,34 @@ var ptrSizeMap = map[string]int64{
 	"arm":   4,
 }
 
-var expandName = map[string]string{
-	"schar":     "signed char",
-	"uchar":     "unsigned char",
-	"ushort":    "unsigned short",
-	"uint":      "unsigned int",
-	"ulong":     "unsigned long",
-	"longlong":  "long long",
-	"ulonglong": "unsigned long long",
-}
-
 func main() {
-	args := os.Args
-	if len(args) < 2 {
+	flag.Usage = usage
+	flag.Parse()
+	args := flag.Args()
+	if len(args) < 1 {
 		usage()
-		os.Exit(2)
 	}
 
 	// Find first arg that looks like a go file and assume everything before
 	// that are options to pass to gcc.
 	var i int
-	for i = len(args) - 1; i > 0; i-- {
-		if !strings.HasSuffix(args[i], ".go") {
+	for i = len(args); i > 0; i-- {
+		if !strings.HasSuffix(args[i-1], ".go") {
 			break
 		}
 	}
-
-	i += 1
-
-	gccOptions, goFiles := args[1:i], args[i:]
+	if i == len(args) {
+		usage()
+	}
+	gccOptions, goFiles := args[0:i], args[i:]
 
 	arch := os.Getenv("GOARCH")
 	if arch == "" {
 		fatal("$GOARCH is not set")
 	}
-	ptrSize, ok := ptrSizeMap[arch]
-	if !ok {
-		fatal("unknown architecture %s", arch)
+	ptrSize := ptrSizeMap[arch]
+	if ptrSize == 0 {
+		fatal("unknown $GOARCH %q", arch)
 	}
 
 	// Clear locale variables so gcc emits English errors [sic].
@@ -69,75 +138,88 @@ func main() {
 	os.Setenv("LC_ALL", "C")
 	os.Setenv("LC_CTYPE", "C")
 
-	p := new(Prog)
-
-	p.PtrSize = ptrSize
-	p.GccOptions = gccOptions
-	p.Vardef = make(map[string]*Type)
-	p.Funcdef = make(map[string]*FuncType)
-	p.Enumdef = make(map[string]int64)
-	p.Constdef = make(map[string]string)
-	p.OutDefs = make(map[string]bool)
+	p := &Package{
+		PtrSize:    ptrSize,
+		GccOptions: gccOptions,
+		Written:    make(map[string]bool),
+	}
 
 	for _, input := range goFiles {
-		// Reset p.Preamble so that we don't end up with conflicting headers / defines
-		p.Preamble = builtinProlog
-		openProg(input, p)
-		for _, cref := range p.Crefs {
-			// Convert C.ulong to C.unsigned long, etc.
-			if expand, ok := expandName[cref.Name]; ok {
-				cref.Name = expand
-			}
-		}
-		p.loadDebugInfo()
-		for _, cref := range p.Crefs {
+		f := new(File)
+		// Reset f.Preamble so that we don't end up with conflicting headers / defines
+		f.Preamble = ""
+		f.ReadGo(input)
+		p.Translate(f)
+		for _, cref := range f.Ref {
 			switch cref.Context {
-			case "const":
-				// This came from a #define and we'll output it later.
-				*cref.Expr = ast.NewIdent(cref.Name)
-				break
-			case "call":
-				if !cref.TypeName {
-					// Is an actual function call.
-					pos := (*cref.Expr).Pos()
-					*cref.Expr = &ast.Ident{Position: pos, Obj: ast.NewObj(ast.Err, pos, "_C_"+cref.Name)}
-					p.Funcdef[cref.Name] = cref.FuncType
-					break
-				}
-				*cref.Expr = cref.Type.Go
-			case "expr":
-				if cref.TypeName {
-					error((*cref.Expr).Pos(), "type C.%s used as expression", cref.Name)
-				}
-				// If the expression refers to an enumerated value, then
-				// place the identifier for the value and add it to Enumdef so
-				// it will be declared as a constant in the later stage.
-				if cref.Type.EnumValues != nil {
-					*cref.Expr = ast.NewIdent(cref.Name)
-					p.Enumdef[cref.Name] = cref.Type.EnumValues[cref.Name]
+			case "call", "call2":
+				if cref.Name.Kind != "type" {
 					break
 				}
-				// Reference to C variable.
-				// We declare a pointer and arrange to have it filled in.
-				*cref.Expr = &ast.StarExpr{X: ast.NewIdent("_C_" + cref.Name)}
-				p.Vardef[cref.Name] = cref.Type
-			case "type":
-				if !cref.TypeName {
-					error((*cref.Expr).Pos(), "expression C.%s used as type", cref.Name)
-				}
-				*cref.Expr = cref.Type.Go
+				*cref.Expr = cref.Name.Type.Go
 			}
 		}
 		if nerrors > 0 {
 			os.Exit(2)
 		}
-		pkg := p.Package
+		pkg := f.Package
 		if dir := os.Getenv("CGOPKGPATH"); dir != "" {
 			pkg = dir + "/" + pkg
 		}
 		p.PackagePath = pkg
-		p.writeOutput(input)
+		p.writeOutput(f, input)
+
+		p.Record(f)
 	}
 
 	p.writeDefs()
 }
+
+// Record what needs to be recorded about f.
+func (p *Package) Record(f *File) {
+	if p.PackageName == "" {
+		p.PackageName = f.Package
+	} else if p.PackageName != f.Package {
+		error(noPos, "inconsistent package names: %s, %s", p.PackageName, f.Package)
+	}
+
+	if p.Typedef == nil {
+		p.Typedef = f.Typedef
+	} else {
+		for k, v := range f.Typedef {
+			if p.Typedef[k] == nil {
+				p.Typedef[k] = v
+			} else if !reflect.DeepEqual(p.Typedef[k], v) {
+				error(noPos, "inconsistent definitions for C type %s", k)
+			}
+		}
+	}
+
+	if p.Name == nil {
+		p.Name = f.Name
+	} else {
+		for k, v := range f.Name {
+			if p.Name[k] == nil {
+				p.Name[k] = v
+			} else if !reflect.DeepEqual(p.Name[k], v) {
+				error(noPos, "inconsistent definitions for C.%s", k)
+			}
+		}
+	}
+
+	if len(f.ExpFunc) > 0 {
+		n := len(p.ExpFunc)
+		ef := make([]*ExpFunc, n+len(f.ExpFunc))
+		copy(ef, p.ExpFunc)
+		copy(ef[n:], f.ExpFunc)
+		p.ExpFunc = ef
+	}
+
+	if len(f.AST.Decls) > 0 {
+		n := len(p.Decl)
+		d := make([]ast.Decl, n+len(f.AST.Decls))
+		copy(d, p.Decl)
+		copy(d[n:], f.AST.Decls)
+		p.Decl = d
+	}
+}
diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index 7cdf483f0e..8b11492e4b 100644
--- a/src/cmd/cgo/out.go
+++ b/src/cmd/cgo/out.go
@@ -5,6 +5,7 @@
 package main
 
 import (
+	"bytes"
 	"fmt"
 	"go/ast"
 	"go/printer"
@@ -13,30 +14,9 @@ import (
 	"strings"
 )
 
-func creat(name string) *os.File {
-	f, err := os.Open(name, os.O_WRONLY|os.O_CREAT|os.O_TRUNC, 0666)
-	if err != nil {
-		fatal("%s", err)
-	}
-	return f
-}
-
-func slashToUnderscore(c int) int {
-	if c == '/' {
-		c = '_'
-	}
-	return c
-}
-
 // writeDefs creates output files to be compiled by 6g, 6c, and gcc.
 // (The comments here say 6g and 6c but the code applies to the 8 and 5 tools too.)
-func (p *Prog) writeDefs() {
-	pkgroot := os.Getenv("GOROOT") + "/pkg/" + os.Getenv("GOOS") + "_" + os.Getenv("GOARCH")
-	path := p.PackagePath
-	if !strings.HasPrefix(path, "/") {
-		path = pkgroot + "/" + path
-	}
-
+func (p *Package) writeDefs() {
 	// The path for the shared object is slash-free so that ELF loaders
 	// will treat it as a relative path.  We rewrite slashes to underscores.
 	sopath := "cgo_" + strings.Map(slashToUnderscore, p.PackagePath)
@@ -53,221 +33,245 @@ func (p *Prog) writeDefs() {
 	// In a separate file so that the import of "unsafe" does not
 	// pollute the original file.
 	fmt.Fprintf(fgo2, "// Created by cgo - DO NOT EDIT\n")
-	fmt.Fprintf(fgo2, "package %s\n\n", p.Package)
+	fmt.Fprintf(fgo2, "package %s\n\n", p.PackageName)
 	fmt.Fprintf(fgo2, "import \"unsafe\"\n\n")
+	fmt.Fprintf(fgo2, "import \"os\"\n\n")
 	fmt.Fprintf(fgo2, "type _ unsafe.Pointer\n\n")
+	fmt.Fprintf(fgo2, "func _Cerrno(dst *os.Error, x int) { *dst = os.Errno(x) }\n")
 
 	for name, def := range p.Typedef {
 		fmt.Fprintf(fgo2, "type %s ", name)
 		printer.Fprint(fgo2, def)
 		fmt.Fprintf(fgo2, "\n")
 	}
-	fmt.Fprintf(fgo2, "type _C_void [0]byte\n")
+	fmt.Fprintf(fgo2, "type _Ctype_void [0]byte\n")
 
 	fmt.Fprintf(fc, cProlog, soprefix, soprefix, soprefix, soprefix, soprefix)
 
-	for name, def := range p.Vardef {
-		fmt.Fprintf(fc, "#pragma dynimport ·_C_%s %s \"%s%s.so\"\n", name, name, soprefix, sopath)
-		fmt.Fprintf(fgo2, "var _C_%s ", name)
-		printer.Fprint(fgo2, &ast.StarExpr{X: def.Go})
+	for _, n := range p.Name {
+		if n.Kind != "var" {
+			continue
+		}
+		fmt.Fprintf(fc, "#pragma dynimport ·%s %s \"%s%s.so\"\n", n.Mangle, n.C, soprefix, sopath)
+		fmt.Fprintf(fgo2, "var %s ", n.Mangle)
+		printer.Fprint(fgo2, &ast.StarExpr{X: n.Type.Go})
 		fmt.Fprintf(fgo2, "\n")
 	}
 	fmt.Fprintf(fc, "\n")
 
-	for name, value := range p.Constdef {
-		fmt.Fprintf(fgo2, "const %s = %s\n", name, value)
-	}
-
-	for name, value := range p.Enumdef {
-		fmt.Fprintf(fgo2, "const %s = %d\n", name, value)
+	for _, n := range p.Name {
+		if n.Const != "" {
+			fmt.Fprintf(fgo2, "const _Cconst_%s = %s\n", n.Go, n.Const)
+		}
 	}
 	fmt.Fprintf(fgo2, "\n")
 
-	for name, def := range p.Funcdef {
-		// Go func declaration.
-		d := &ast.FuncDecl{
-			Name: ast.NewIdent("_C_" + name),
-			Type: def.Go,
+	for _, n := range p.Name {
+		if n.FuncType != nil {
+			p.writeDefsFunc(fc, fgo2, n, soprefix, sopath)
 		}
-		printer.Fprint(fgo2, d)
-		fmt.Fprintf(fgo2, "\n")
+	}
 
-		if name == "CString" || name == "GoString" {
-			// The builtins are already defined in the C prolog.
-			continue
-		}
+	p.writeExports(fgo2, fc)
 
-		// Construct a gcc struct matching the 6c argument frame.
-		// Assumes that in gcc, char is 1 byte, short 2 bytes, int 4 bytes, long long 8 bytes.
-		// These assumptions are checked by the gccProlog.
-		// Also assumes that 6c convention is to word-align the
-		// input and output parameters.
-		structType := "struct {\n"
-		off := int64(0)
-		npad := 0
-		for i, t := range def.Params {
-			if off%t.Align != 0 {
-				pad := t.Align - off%t.Align
-				structType += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
-				off += pad
-				npad++
-			}
-			structType += fmt.Sprintf("\t\t%s p%d;\n", t.C, i)
-			off += t.Size
-		}
-		if off%p.PtrSize != 0 {
-			pad := p.PtrSize - off%p.PtrSize
-			structType += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
+	fgo2.Close()
+	fc.Close()
+}
+
+// Construct a gcc struct matching the 6c argument frame.
+// Assumes that in gcc, char is 1 byte, short 2 bytes, int 4 bytes, long long 8 bytes.
+// These assumptions are checked by the gccProlog.
+// Also assumes that 6c convention is to word-align the
+// input and output parameters.
+func (p *Package) structType(n *Name) (string, int64) {
+	var buf bytes.Buffer
+	fmt.Fprint(&buf, "struct {\n")
+	off := int64(0)
+	for i, t := range n.FuncType.Params {
+		if off%t.Align != 0 {
+			pad := t.Align - off%t.Align
+			fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
 			off += pad
-			npad++
 		}
-		if t := def.Result; t != nil {
-			if off%t.Align != 0 {
-				pad := t.Align - off%t.Align
-				structType += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
-				off += pad
-				npad++
-			}
-			structType += fmt.Sprintf("\t\t%s r;\n", t.C)
-			off += t.Size
-		}
-		if off%p.PtrSize != 0 {
-			pad := p.PtrSize - off%p.PtrSize
-			structType += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
+		fmt.Fprintf(&buf, "\t\t%s p%d;\n", t.C, i)
+		off += t.Size
+	}
+	if off%p.PtrSize != 0 {
+		pad := p.PtrSize - off%p.PtrSize
+		fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
+		off += pad
+	}
+	if t := n.FuncType.Result; t != nil {
+		if off%t.Align != 0 {
+			pad := t.Align - off%t.Align
+			fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
 			off += pad
-			npad++
 		}
-		if len(def.Params) == 0 && def.Result == nil {
-			structType += "\t\tchar unused;\n" // avoid empty struct
-			off++
+		fmt.Fprintf(&buf, "\t\t%s r;\n", t.C)
+		off += t.Size
+	}
+	if off%p.PtrSize != 0 {
+		pad := p.PtrSize - off%p.PtrSize
+		fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
+		off += pad
+	}
+	if n.AddError {
+		fmt.Fprint(&buf, "\t\tvoid *e[2]; /* os.Error */\n")
+		off += 2 * p.PtrSize
+	}
+	if off == 0 {
+		fmt.Fprintf(&buf, "\t\tchar unused;\n") // avoid empty struct
+		off++
+	}
+	fmt.Fprintf(&buf, "\t}\n")
+	return buf.String(), off
+}
+
+func (p *Package) writeDefsFunc(fc, fgo2 *os.File, n *Name, soprefix, sopath string) {
+	name := n.Go
+	gtype := n.FuncType.Go
+	if n.AddError {
+		// Add "os.Error" to return type list.
+		// Type list is known to be 0 or 1 element - it's a C function.
+		err := &ast.Field{Type: ast.NewIdent("os.Error")}
+		l := gtype.Results.List
+		if len(l) == 0 {
+			l = []*ast.Field{err}
+		} else {
+			l = []*ast.Field{l[0], err}
 		}
-		structType += "\t}"
-		argSize := off
-
-		// C wrapper calls into gcc, passing a pointer to the argument frame.
-		// Also emit #pragma to get a pointer to the gcc wrapper.
-		fmt.Fprintf(fc, "#pragma dynimport _cgo_%s _cgo_%s \"%s%s.so\"\n", name, name, soprefix, sopath)
-		fmt.Fprintf(fc, "void (*_cgo_%s)(void*);\n", name)
-		fmt.Fprintf(fc, "\n")
-		fmt.Fprintf(fc, "void\n")
-		fmt.Fprintf(fc, "·_C_%s(struct{uint8 x[%d];}p)\n", name, argSize)
-		fmt.Fprintf(fc, "{\n")
-		fmt.Fprintf(fc, "\tcgocall(_cgo_%s, &p);\n", name)
-		fmt.Fprintf(fc, "}\n")
-		fmt.Fprintf(fc, "\n")
+		t := new(ast.FuncType)
+		*t = *gtype
+		t.Results = &ast.FieldList{List: l}
+		gtype = t
 	}
 
-	p.writeExports(fgo2, fc)
+	// Go func declaration.
+	d := &ast.FuncDecl{
+		Name: ast.NewIdent(n.Mangle),
+		Type: gtype,
+	}
+	printer.Fprint(fgo2, d)
+	fmt.Fprintf(fgo2, "\n")
 
-	fgo2.Close()
-	fc.Close()
+	if name == "CString" || name == "GoString" {
+		// The builtins are already defined in the C prolog.
+		return
+	}
+
+	var argSize int64
+	_, argSize = p.structType(n)
+
+	// C wrapper calls into gcc, passing a pointer to the argument frame.
+	// Also emit #pragma to get a pointer to the gcc wrapper.
+	fmt.Fprintf(fc, "#pragma dynimport _cgo%s _cgo%s \"%s%s.so\"\n", n.Mangle, n.Mangle, soprefix, sopath)
+	fmt.Fprintf(fc, "void (*_cgo%s)(void*);\n", n.Mangle)
+	fmt.Fprintf(fc, "\n")
+	fmt.Fprintf(fc, "void\n")
+	fmt.Fprintf(fc, "·%s(struct{uint8 x[%d];}p)\n", n.Mangle, argSize)
+	fmt.Fprintf(fc, "{\n")
+	fmt.Fprintf(fc, "\tcgocall(_cgo%s, &p);\n", n.Mangle)
+	if n.AddError {
+		// gcc leaves errno in first word of interface at end of p.
+		// check whether it is zero; if so, turn interface into nil.
+		// if not, turn interface into errno.
+		// Go init function initializes ·_Cerrno with an os.Errno
+		// for us to copy.
+		fmt.Fprintln(fc, `	{
+			int32 e;
+			void **v;
+			v = (void**)(&p+1) - 2;	/* v = final two void* of p */
+			e = *(int32*)v;
+			v[0] = (void*)0xdeadbeef;
+			v[1] = (void*)0xdeadbeef;
+			if(e == 0) {
+				/* nil interface */
+				v[0] = 0;
+				v[1] = 0;
+			} else {
+				·_Cerrno(v, e);	/* fill in v as os.Error for errno e */
+			}
+		}`)
+	}
+	fmt.Fprintf(fc, "}\n")
+	fmt.Fprintf(fc, "\n")
 }
 
 // writeOutput creates stubs for a specific source file to be compiled by 6g
 // (The comments here say 6g and 6c but the code applies to the 8 and 5 tools too.)
-func (p *Prog) writeOutput(srcfile string) {
+func (p *Package) writeOutput(f *File, srcfile string) {
 	base := srcfile
 	if strings.HasSuffix(base, ".go") {
 		base = base[0 : len(base)-3]
 	}
+	base = strings.Map(slashToUnderscore, base)
 	fgo1 := creat(base + ".cgo1.go")
 	fgcc := creat(base + ".cgo2.c")
 
 	// Write Go output: Go input with rewrites of C.xxx to _C_xxx.
 	fmt.Fprintf(fgo1, "// Created by cgo - DO NOT EDIT\n")
 	fmt.Fprintf(fgo1, "//line %s:1\n", srcfile)
-	printer.Fprint(fgo1, p.AST)
+	printer.Fprint(fgo1, f.AST)
 
 	// While we process the vars and funcs, also write 6c and gcc output.
 	// Gcc output starts with the preamble.
-	fmt.Fprintf(fgcc, "%s\n", p.Preamble)
+	fmt.Fprintf(fgcc, "%s\n", f.Preamble)
 	fmt.Fprintf(fgcc, "%s\n", gccProlog)
 
-	for name, def := range p.Funcdef {
-		_, ok := p.OutDefs[name]
-		if name == "CString" || name == "GoString" || ok {
-			// The builtins are already defined in the C prolog, and we don't
-			// want to duplicate function definitions we've already done.
-			continue
-		}
-		p.OutDefs[name] = true
-
-		// Construct a gcc struct matching the 6c argument frame.
-		// Assumes that in gcc, char is 1 byte, short 2 bytes, int 4 bytes, long long 8 bytes.
-		// These assumptions are checked by the gccProlog.
-		// Also assumes that 6c convention is to word-align the
-		// input and output parameters.
-		structType := "struct {\n"
-		off := int64(0)
-		npad := 0
-		for i, t := range def.Params {
-			if off%t.Align != 0 {
-				pad := t.Align - off%t.Align
-				structType += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
-				off += pad
-				npad++
-			}
-			structType += fmt.Sprintf("\t\t%s p%d;\n", t.C, i)
-			off += t.Size
-		}
-		if off%p.PtrSize != 0 {
-			pad := p.PtrSize - off%p.PtrSize
-			structType += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
-			off += pad
-			npad++
-		}
-		if t := def.Result; t != nil {
-			if off%t.Align != 0 {
-				pad := t.Align - off%t.Align
-				structType += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
-				off += pad
-				npad++
-			}
-			structType += fmt.Sprintf("\t\t%s r;\n", t.C)
-			off += t.Size
-		}
-		if off%p.PtrSize != 0 {
-			pad := p.PtrSize - off%p.PtrSize
-			structType += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
-			off += pad
-			npad++
-		}
-		if len(def.Params) == 0 && def.Result == nil {
-			structType += "\t\tchar unused;\n" // avoid empty struct
-			off++
-		}
-		structType += "\t}"
-
-		// Gcc wrapper unpacks the C argument struct
-		// and calls the actual C function.
-		fmt.Fprintf(fgcc, "void\n")
-		fmt.Fprintf(fgcc, "_cgo_%s(void *v)\n", name)
-		fmt.Fprintf(fgcc, "{\n")
-		fmt.Fprintf(fgcc, "\t%s *a = v;\n", structType)
-		fmt.Fprintf(fgcc, "\t")
-		if def.Result != nil {
-			fmt.Fprintf(fgcc, "a->r = ")
-		}
-		fmt.Fprintf(fgcc, "%s(", name)
-		for i := range def.Params {
-			if i > 0 {
-				fmt.Fprintf(fgcc, ", ")
-			}
-			fmt.Fprintf(fgcc, "a->p%d", i)
+	for _, n := range f.Name {
+		if n.FuncType != nil {
+			p.writeOutputFunc(fgcc, n)
 		}
-		fmt.Fprintf(fgcc, ");\n")
-		fmt.Fprintf(fgcc, "}\n")
-		fmt.Fprintf(fgcc, "\n")
 	}
 
 	fgo1.Close()
 	fgcc.Close()
 }
 
+func (p *Package) writeOutputFunc(fgcc *os.File, n *Name) {
+	name := n.Mangle
+	if name == "_Cfunc_CString" || name == "_Cfunc_GoString" || p.Written[name] {
+		// The builtins are already defined in the C prolog, and we don't
+		// want to duplicate function definitions we've already done.
+		return
+	}
+	p.Written[name] = true
+
+	ctype, _ := p.structType(n)
+
+	// Gcc wrapper unpacks the C argument struct
+	// and calls the actual C function.
+	fmt.Fprintf(fgcc, "void\n")
+	fmt.Fprintf(fgcc, "_cgo%s(void *v)\n", n.Mangle)
+	fmt.Fprintf(fgcc, "{\n")
+	if n.AddError {
+		fmt.Fprintf(fgcc, "\tint e;\n") // assuming 32 bit (see comment above structType)
+		fmt.Fprintf(fgcc, "\terrno = 0;\n")
+	}
+	fmt.Fprintf(fgcc, "\t%s *a = v;\n", ctype)
+	fmt.Fprintf(fgcc, "\t")
+	if n.FuncType.Result != nil {
+		fmt.Fprintf(fgcc, "a->r = ")
+	}
+	fmt.Fprintf(fgcc, "%s(", n.C)
+	for i := range n.FuncType.Params {
+		if i > 0 {
+			fmt.Fprintf(fgcc, ", ")
+		}
+		fmt.Fprintf(fgcc, "a->p%d", i)
+	}
+	fmt.Fprintf(fgcc, ");\n")
+	if n.AddError {
+		fmt.Fprintf(fgcc, "\t*(int*)(a->e) = errno;\n")
+	}
+	fmt.Fprintf(fgcc, "}\n")
+	fmt.Fprintf(fgcc, "\n")
+}
+
 // Write out the various stubs we need to support functions exported
 // from Go so that they are callable from C.
-func (p *Prog) writeExports(fgo2, fc *os.File) {
-	if len(p.ExpFuncs) == 0 {
+func (p *Package) writeExports(fgo2, fc *os.File) {
+	if len(p.ExpFunc) == 0 {
 		return
 	}
 
@@ -280,17 +284,17 @@ func (p *Prog) writeExports(fgo2, fc *os.File) {
 	fmt.Fprintf(fgcc, "/* Created by cgo - DO NOT EDIT. */\n")
 	fmt.Fprintf(fgcc, "#include \"_cgo_export.h\"\n")
 
-	for _, exp := range p.ExpFuncs {
+	for _, exp := range p.ExpFunc {
 		fn := exp.Func
 
 		// Construct a gcc struct matching the 6c argument and
 		// result frame.
-		structType := "struct {\n"
+		ctype := "struct {\n"
 		off := int64(0)
 		npad := 0
 		if fn.Recv != nil {
 			t := p.cgoType(fn.Recv.List[0].Type)
-			structType += fmt.Sprintf("\t\t%s recv;\n", t.C)
+			ctype += fmt.Sprintf("\t\t%s recv;\n", t.C)
 			off += t.Size
 		}
 		fntype := fn.Type
@@ -299,16 +303,16 @@ func (p *Prog) writeExports(fgo2, fc *os.File) {
 				t := p.cgoType(atype)
 				if off%t.Align != 0 {
 					pad := t.Align - off%t.Align
-					structType += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
+					ctype += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
 					off += pad
 					npad++
 				}
-				structType += fmt.Sprintf("\t\t%s p%d;\n", t.C, i)
+				ctype += fmt.Sprintf("\t\t%s p%d;\n", t.C, i)
 				off += t.Size
 			})
 		if off%p.PtrSize != 0 {
 			pad := p.PtrSize - off%p.PtrSize
-			structType += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
+			ctype += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
 			off += pad
 			npad++
 		}
@@ -317,24 +321,24 @@ func (p *Prog) writeExports(fgo2, fc *os.File) {
 				t := p.cgoType(atype)
 				if off%t.Align != 0 {
 					pad := t.Align - off%t.Align
-					structType += fmt.Sprintf("\t\tchar __pad%d[%d]\n", npad, pad)
+					ctype += fmt.Sprintf("\t\tchar __pad%d[%d]\n", npad, pad)
 					off += pad
 					npad++
 				}
-				structType += fmt.Sprintf("\t\t%s r%d;\n", t.C, i)
+				ctype += fmt.Sprintf("\t\t%s r%d;\n", t.C, i)
 				off += t.Size
 			})
 		if off%p.PtrSize != 0 {
 			pad := p.PtrSize - off%p.PtrSize
-			structType += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
+			ctype += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
 			off += pad
 			npad++
 		}
-		if structType == "struct {\n" {
-			structType += "\t\tchar unused;\n" // avoid empty struct
+		if ctype == "struct {\n" {
+			ctype += "\t\tchar unused;\n" // avoid empty struct
 			off++
 		}
-		structType += "\t}"
+		ctype += "\t}"
 
 		// Get the return type of the wrapper function
 		// compiled by gcc.
@@ -373,7 +377,7 @@ func (p *Prog) writeExports(fgo2, fc *os.File) {
 		fmt.Fprintf(fgcc, "extern _cgoexp_%s(void *, int);\n", exp.ExpName)
 		fmt.Fprintf(fgcc, "\n%s\n", s)
 		fmt.Fprintf(fgcc, "{\n")
-		fmt.Fprintf(fgcc, "\t%s a;\n", structType)
+		fmt.Fprintf(fgcc, "\t%s a;\n", ctype)
 		if gccResult != "void" && (len(fntype.Results.List) > 1 || len(fntype.Results.List[0].Names) > 1) {
 			fmt.Fprintf(fgcc, "\t%s r;\n", gccResult)
 		}
@@ -493,7 +497,7 @@ var goTypes = map[string]*Type{
 }
 
 // Map an ast type to a Type.
-func (p *Prog) cgoType(e ast.Expr) *Type {
+func (p *Package) cgoType(e ast.Expr) *Type {
 	switch t := e.(type) {
 	case *ast.StarExpr:
 		x := p.cgoType(t.X)
@@ -515,7 +519,7 @@ func (p *Prog) cgoType(e ast.Expr) *Type {
 	case *ast.Ident:
 		// Look up the type in the top level declarations.
 		// TODO: Handle types defined within a function.
-		for _, d := range p.AST.Decls {
+		for _, d := range p.Decl {
 			gd, ok := d.(*ast.GenDecl)
 			if !ok || gd.Tok != token.TYPE {
 				continue
@@ -568,6 +572,9 @@ typedef long long __cgo_long_long;
 __cgo_size_assert(__cgo_long_long, 8)
 __cgo_size_assert(float, 4)
 __cgo_size_assert(double, 8)
+
+#include <errno.h>
+#include <string.h>
 `
 
 const builtinProlog = `
@@ -586,15 +593,17 @@ const cProlog = `
 #pragma dynimport _cgo_malloc _cgo_malloc "%slibcgo.so"
 #pragma dynimport _cgo_free _cgo_free "%slibcgo.so"
 
+void ·_Cerrno(void*, int32);
+
 void
-·_C_GoString(int8 *p, String s)
+·_Cfunc_GoString(int8 *p, String s)
 {
 	s = gostring((byte*)p);
 	FLUSH(&s);
 }
 
 void
-·_C_CString(String s, int8 *p)
+·_Cfunc_CString(String s, int8 *p)
 {
 	p = cmalloc(s.len+1);
 	mcpy((byte*)p, s.str, s.len);
diff --git a/src/cmd/cgo/util.go b/src/cmd/cgo/util.go
index 95067039ca..3911982951 100644
--- a/src/cmd/cgo/util.go
+++ b/src/cmd/cgo/util.go
@@ -12,16 +12,6 @@ import (
 	"os"
 )
 
-// A ByteReaderAt implements io.ReadAt using a slice of bytes.
-type ByteReaderAt []byte
-
-func (r ByteReaderAt) ReadAt(p []byte, off int64) (n int, err os.Error) {
-	if off >= int64(len(r)) || off < 0 {
-		return 0, os.EOF
-	}
-	return copy(p, r[off:]), nil
-}
-
 // run runs the command argv, feeding in stdin on standard input.
 // It returns the output to standard output and standard error.
 // ok indicates whether the command exited successfully.
@@ -92,3 +82,38 @@ func error(pos token.Position, msg string, args ...interface{}) {
 	fmt.Fprintf(os.Stderr, msg, args)
 	fmt.Fprintf(os.Stderr, "\n")
 }
+
+// isName returns true if s is a valid C identifier
+func isName(s string) bool {
+	for i, v := range s {
+		if v != '_' && (v < 'A' || v > 'Z') && (v < 'a' || v > 'z') && (v < '0' || v > '9') {
+			return false
+		}
+		if i == 0 && '0' <= v && v <= '9' {
+			return false
+		}
+	}
+	return s != ""
+}
+
+func creat(name string) *os.File {
+	f, err := os.Open(name, os.O_WRONLY|os.O_CREAT|os.O_TRUNC, 0666)
+	if err != nil {
+		fatal("%s", err)
+	}
+	return f
+}
+
+func slashToUnderscore(c int) int {
+	if c == '/' {
+		c = '_'
+	}
+	return c
+}
+
+func concat(a, b []string) []string {
+	c := make([]string, len(a)+len(b))
+	copy(c, a)
+	copy(c[len(a):], b)
+	return c
+}