Fix bitfields on big-endian machines

2 files changed, 61 insertions, 8 deletions

diff --git a/c/_cffi_backend.c b/c/_cffi_backend.c
index cfbf5af..c002ccf 100644
--- a/c/_cffi_backend.c
+++ b/c/_cffi_backend.c
@@ -3489,6 +3489,7 @@ _add_field(PyObject *interned_fields, PyObject *fname, CTypeDescrObject *ftype,
 
 #define SF_MSVC_BITFIELDS 1
 #define SF_GCC_ARM_BITFIELDS 2
+#define SF_GCC_BIG_ENDIAN 4
 
 static PyObject *b_complete_struct_or_union(PyObject *self, PyObject *args)
 {
@@ -3508,6 +3509,9 @@ static PyObject *b_complete_struct_or_union(PyObject *self, PyObject *args)
 # else
     int sflags = 0;
 # endif
+    int _check_endian = 1;
+    if (*(char *)&_check_endian == 0)
+        sflags |= SF_GCC_BIG_ENDIAN;
 #endif
 
     if (!PyArg_ParseTuple(args, "O!O!|Onii:complete_struct_or_union",
@@ -3743,6 +3747,9 @@ static PyObject *b_complete_struct_or_union(PyObject *self, PyObject *args)
                     field_offset_bytes = boffset / 8 - ftype->ct_size;
                 }
 
+                if (sflags & SF_GCC_BIG_ENDIAN)
+                    bitshift = 8 * ftype->ct_size - fbitsize - bitshift;
+
                 *previous = _add_field(interned_fields, fname, ftype,
                                        field_offset_bytes, bitshift, fbitsize);
                 if (*previous == NULL)
diff --git a/c/test_c.py b/c/test_c.py
index 02a4d03..1e98b65 100644
--- a/c/test_c.py
+++ b/c/test_c.py
@@ -1527,13 +1527,18 @@ def test_struct_with_bitfields():
     d = BStruct.fields
     assert d[0][1].offset == d[1][1].offset == d[2][1].offset == 0
     assert d[3][1].offset == sizeof(BLong)
-    assert d[0][1].bitshift == 0
+    def f(m, r):
+        if sys.byteorder == 'little':
+            return r
+        else:
+            return LONGBITS - m - r
+    assert d[0][1].bitshift == f(1, 0)
     assert d[0][1].bitsize == 1
-    assert d[1][1].bitshift == 1
+    assert d[1][1].bitshift == f(2, 1)
     assert d[1][1].bitsize == 2
-    assert d[2][1].bitshift == 3
+    assert d[2][1].bitshift == f(3, 3)
     assert d[2][1].bitsize == 3
-    assert d[3][1].bitshift == 0
+    assert d[3][1].bitshift == f(LONGBITS - 5, 0)
     assert d[3][1].bitsize == LONGBITS - 5
     assert sizeof(BStruct) == 2 * sizeof(BLong)
     assert alignof(BStruct) == alignof(BLong)
@@ -2867,7 +2872,7 @@ def _test_bitfield_details(flag):
                                        ('b1', BInt, 9),
                                        ('b2', BUInt, 7),
                                        ('c', BChar, -1)], -1, -1, -1, flag)
-    if flag % 2 == 0:   # gcc and gcc ARM
+    if flag % 2 == 0:   # gcc, any variant
         assert typeoffsetof(BStruct, 'c') == (BChar, 3)
         assert sizeof(BStruct) == 4
     else:               # msvc
@@ -2875,6 +2880,31 @@ def _test_bitfield_details(flag):
         assert sizeof(BStruct) == 12
     assert alignof(BStruct) == 4
     #
+    p = newp(new_pointer_type(BStruct), None)
+    p.a = b'A'
+    p.b1 = -201
+    p.b2 = 99
+    p.c = b'\x9D'
+    raw = buffer(p)[:]
+    if sys.byteorder == 'little':
+        if flag == 0 or flag == 2:  # gcc, little endian
+            assert raw == b'A7\xC7\x9D'
+        elif flag == 1: # msvc
+            assert raw == b'A\x00\x00\x007\xC7\x00\x00\x9D\x00\x00\x00'
+        elif flag == 4: # gcc, big endian
+            assert raw == b'A\xE3\x9B\x9D'
+        else:
+            raise AssertionError("bad flag")
+    else:
+        if flag == 0 or flag == 2:  # gcc
+            assert raw == b'A\xC77\x9D'
+        elif flag == 1: # msvc
+            assert raw == b'A\x00\x00\x00\x00\x00\xC77\x9D\x00\x00\x00'
+        elif flag == 4: # gcc, big endian
+            assert raw == b'A\x9B\xE3\x9D'
+        else:
+            raise AssertionError("bad flag")
+    #
     BStruct = new_struct_type("struct foo2")
     complete_struct_or_union(BStruct, [('a', BChar, -1),
                                        ('',  BShort, 9),
@@ -2886,16 +2916,21 @@ def _test_bitfield_details(flag):
     elif flag == 1: # msvc
         assert sizeof(BStruct) == 6
         assert alignof(BStruct) == 2
-    else:           # gcc ARM
+    elif flag == 2: # gcc ARM
         assert sizeof(BStruct) == 6
         assert alignof(BStruct) == 2
+    elif flag == 4: # gcc, big endian
+        assert sizeof(BStruct) == 5
+        assert alignof(BStruct) == 1
+    else:
+        raise AssertionError("bad flag")
     #
     BStruct = new_struct_type("struct foo2")
     complete_struct_or_union(BStruct, [('a', BChar, -1),
                                        ('',  BInt, 0),
                                        ('',  BInt, 0),
                                        ('c', BChar, -1)], -1, -1, -1, flag)
-    if flag == 0:   # gcc
+    if flag == 0:    # gcc
         assert typeoffsetof(BStruct, 'c') == (BChar, 4)
         assert sizeof(BStruct) == 5
         assert alignof(BStruct) == 1
@@ -2903,10 +2938,16 @@ def _test_bitfield_details(flag):
         assert typeoffsetof(BStruct, 'c') == (BChar, 1)
         assert sizeof(BStruct) == 2
         assert alignof(BStruct) == 1
-    else:            # gcc ARM
+    elif flag == 2:  # gcc ARM
         assert typeoffsetof(BStruct, 'c') == (BChar, 4)
         assert sizeof(BStruct) == 8
         assert alignof(BStruct) == 4
+    elif flag == 4:  # gcc, big endian
+        assert typeoffsetof(BStruct, 'c') == (BChar, 4)
+        assert sizeof(BStruct) == 5
+        assert alignof(BStruct) == 1
+    else:
+        raise AssertionError("bad flag")
 
 
 def test_bitfield_as_gcc():
@@ -2918,6 +2959,11 @@ def test_bitfield_as_msvc():
 def test_bitfield_as_arm_gcc():
     _test_bitfield_details(flag=2)
 
+def test_bitfield_as_big_endian():
+    if '__pypy__' in sys.builtin_module_names:
+        py.test.skip("no big endian machine supported on pypy for now")
+    _test_bitfield_details(flag=4)
+
 
 def test_version():
     # this test is here mostly for PyPy