Issue 131: support ffi.cdef("...", packed=True)

2 files changed, 31 insertions, 2 deletions

diff --git a/c/_cffi_backend.c b/c/_cffi_backend.c
index 1fa38bc..85fe49d 100644
--- a/c/_cffi_backend.c
+++ b/c/_cffi_backend.c
@@ -3586,6 +3586,7 @@ _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
+#define SF_PACKED 8
 
 static PyObject *b_complete_struct_or_union(PyObject *self, PyObject *args)
 {
@@ -3671,8 +3672,8 @@ static PyObject *b_complete_struct_or_union(PyObject *self, PyObject *args)
             boffset = 0;   /* reset each field at offset 0 */
 
         /* update the total alignment requirement, but skip it if the
-           field is an anonymous bitfield */
-        falign = get_alignment(ftype);
+           field is an anonymous bitfield or if SF_PACKED */
+        falign = (sflags & SF_PACKED) ? 1 : get_alignment(ftype);
         if (falign < 0)
             goto error;
 
diff --git a/c/test_c.py b/c/test_c.py
index 6249260..005a089 100644
--- a/c/test_c.py
+++ b/c/test_c.py
@@ -3148,6 +3148,34 @@ def test_sizeof_sliced_array():
     p = newp(BArray, None)
     assert sizeof(p[2:9]) == 7 * sizeof(BInt)
 
+def test_packed():
+    BLong = new_primitive_type("long")
+    BChar = new_primitive_type("char")
+    BShort = new_primitive_type("short")
+    BStruct = new_struct_type("struct foo")
+    complete_struct_or_union(BStruct, [('a1', BLong, -1),
+                                       ('a2', BChar, -1),
+                                       ('a3', BShort, -1)],
+                             None, -1, -1, 8)   # SF_PACKED==8
+    d = BStruct.fields
+    assert len(d) == 3
+    assert d[0][0] == 'a1'
+    assert d[0][1].type is BLong
+    assert d[0][1].offset == 0
+    assert d[0][1].bitshift == -1
+    assert d[0][1].bitsize == -1
+    assert d[1][0] == 'a2'
+    assert d[1][1].type is BChar
+    assert d[1][1].offset == sizeof(BLong)
+    assert d[1][1].bitshift == -1
+    assert d[1][1].bitsize == -1
+    assert d[2][0] == 'a3'
+    assert d[2][1].type is BShort
+    assert d[2][1].offset == sizeof(BLong) + sizeof(BChar)
+    assert d[2][1].bitshift == -1
+    assert d[2][1].bitsize == -1
+    assert sizeof(BStruct) == sizeof(BLong) + sizeof(BChar) + sizeof(BShort)
+    assert alignof(BStruct) == 1
 
 def test_version():
     # this test is here mostly for PyPy