2 files changed, 59 insertions, 0 deletions
diff --git a/misc/cgo/testgodefs/testdata/bitfields.go b/misc/cgo/testgodefs/testdata/bitfields.go
new file mode 100644
index 0000000000..6a9724dcd1
--- /dev/null
+++ b/misc/cgo/testgodefs/testdata/bitfields.go
@@ -0,0 +1,31 @@
+// Copyright 2020 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.
+//
+// +build ignore
+
+package main
+
+// This file tests that we don't generate an incorrect field location
+// for a bitfield that appears aligned.
+
+/*
+struct bitfields {
+    unsigned int B1     :  5;
+    unsigned int B2     :  1;
+    unsigned int B3     :  1;
+    unsigned int B4     :  1;
+    unsigned int Short1 : 16; // misaligned on 8 bit boundary
+    unsigned int B5     :  1;
+    unsigned int B6     :  1;
+    unsigned int B7     :  1;
+    unsigned int B8     :  1;
+    unsigned int B9     :  1;
+    unsigned int B10    :  3;
+    unsigned int Short2 : 16; // alignment is OK
+    unsigned int Short3 : 16; // alignment is OK
+};
+*/
+import "C"
+
+type bitfields C.struct_bitfields
diff --git a/misc/cgo/testgodefs/testdata/main.go b/misc/cgo/testgodefs/testdata/main.go
index 2e1ad3376a..4a3f6a701c 100644
--- a/misc/cgo/testgodefs/testdata/main.go
+++ b/misc/cgo/testgodefs/testdata/main.go
@@ -4,6 +4,12 @@
 
 package main
 
+import (
+	"fmt"
+	"os"
+	"reflect"
+)
+
 // Test that the struct field in anonunion.go was promoted.
 var v1 T
 var v2 = v1.L
@@ -23,4 +29,26 @@ var v7 = S{}
 var _ = issue38649{X: 0}
 
 func main() {
+	pass := true
+
+	// The Go translation of bitfields should not have any of the
+	// bitfield types. The order in which bitfields are laid out
+	// in memory is implementation defined, so we can't easily
+	// know how a bitfield should correspond to a Go type, even if
+	// it appears to be aligned correctly.
+	bitfieldType := reflect.TypeOf(bitfields{})
+	check := func(name string) {
+		_, ok := bitfieldType.FieldByName(name)
+		if ok {
+			fmt.Fprintf(os.Stderr, "found unexpected bitfields field %s\n", name)
+			pass = false
+		}
+	}
+	check("Short1")
+	check("Short2")
+	check("Short3")
+
+	if !pass {
+		os.Exit(1)
+	}
 }