1 files changed, 22 insertions, 4 deletions
diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go
index 84f4978f63..b64849a8d1 100644
--- a/src/cmd/cgo/gcc.go
+++ b/src/cmd/cgo/gcc.go
@@ -1544,11 +1544,13 @@ func (c *typeConv) intExpr(n int64) ast.Expr {
 }
 
 // Add padding of given size to fld.
-func (c *typeConv) pad(fld []*ast.Field, size int64) []*ast.Field {
+func (c *typeConv) pad(fld []*ast.Field, sizes []int64, size int64) ([]*ast.Field, []int64) {
 	n := len(fld)
 	fld = fld[0 : n+1]
 	fld[n] = &ast.Field{Names: []*ast.Ident{c.Ident("_")}, Type: c.Opaque(size)}
-	return fld
+	sizes = sizes[0 : n+1]
+	sizes[n] = size
+	return fld, sizes
 }
 
 // Struct conversion: return Go and (gc) C syntax for type.
@@ -1559,6 +1561,7 @@ func (c *typeConv) Struct(dt *dwarf.StructType, pos token.Pos) (expr *ast.Struct
 	var buf bytes.Buffer
 	buf.WriteString("struct {")
 	fld := make([]*ast.Field, 0, 2*len(dt.Field)+1) // enough for padding around every field
+	sizes := make([]int64, 0, 2*len(dt.Field)+1)
 	off := int64(0)
 
 	// Rename struct fields that happen to be named Go keywords into
@@ -1594,7 +1597,7 @@ func (c *typeConv) Struct(dt *dwarf.StructType, pos token.Pos) (expr *ast.Struct
 	anon := 0
 	for _, f := range dt.Field {
 		if f.ByteOffset > off {
-			fld = c.pad(fld, f.ByteOffset-off)
+			fld, sizes = c.pad(fld, sizes, f.ByteOffset-off)
 			off = f.ByteOffset
 		}
 
@@ -1652,6 +1655,8 @@ func (c *typeConv) Struct(dt *dwarf.StructType, pos token.Pos) (expr *ast.Struct
 			ident[name] = name
 		}
 		fld[n] = &ast.Field{Names: []*ast.Ident{c.Ident(ident[name])}, Type: tgo}
+		sizes = sizes[0 : n+1]
+		sizes[n] = size
 		off += size
 		buf.WriteString(t.C.String())
 		buf.WriteString(" ")
@@ -1662,9 +1667,22 @@ func (c *typeConv) Struct(dt *dwarf.StructType, pos token.Pos) (expr *ast.Struct
 		}
 	}
 	if off < dt.ByteSize {
-		fld = c.pad(fld, dt.ByteSize-off)
+		fld, sizes = c.pad(fld, sizes, dt.ByteSize-off)
 		off = dt.ByteSize
 	}
+
+	// If the last field in a non-zero-sized struct is zero-sized
+	// the compiler is going to pad it by one (see issue 9401).
+	// We can't permit that, because then the size of the Go
+	// struct will not be the same as the size of the C struct.
+	// Our only option in such a case is to remove the field,
+	// which means that it can not be referenced from Go.
+	for off > 0 && sizes[len(sizes)-1] == 0 {
+		n := len(sizes)
+		fld = fld[0 : n-1]
+		sizes = sizes[0 : n-1]
+	}
+
 	if off != dt.ByteSize {
 		fatalf("%s: struct size calculation error off=%d bytesize=%d", lineno(pos), off, dt.ByteSize)
 	}