Fix Tools/gdb/libpython.py

Backport https://github.com/python/cpython/commit/11659d00b9185c8f02ea6b642fa475a80e21f1a9
into this change instead of leaving it a separate followup change.

4 files changed, 18 insertions, 25 deletions

diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-04-19-08-30-07.bpo-33312.mDe2iL.rst b/Misc/NEWS.d/next/Core and Builtins/2018-04-19-08-30-07.bpo-33312.mDe2iL.rst
new file mode 100644
index 0000000..40b51b9
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-04-19-08-30-07.bpo-33312.mDe2iL.rst
@@ -0,0 +1,3 @@
+Fixed clang ubsan (undefined behavior sanitizer) warnings in dictobject.c by
+adjusting how the internal struct _dictkeysobject shared keys structure is
+declared.
diff --git a/Objects/dict-common.h b/Objects/dict-common.h
index ce9edab..d3ae07b 100644
--- a/Objects/dict-common.h
+++ b/Objects/dict-common.h
@@ -59,15 +59,8 @@ struct _dictkeysobject {
        - 4 bytes if dk_size <= 0xffffffff (int32_t*)
        - 8 bytes otherwise (int64_t*)
 
-       Dynamically sized, 8 is minimum. */
-    union {
-        int8_t as_1[8];
-        int16_t as_2[4];
-        int32_t as_4[2];
-#if SIZEOF_VOID_P > 4
-        int64_t as_8[1];
-#endif
-    } dk_indices;
+       Dynamically sized, SIZEOF_VOID_P is minimum. */
+    char dk_indices[];  /* char is required to avoid strict aliasing. */
 
     /* "PyDictKeyEntry dk_entries[dk_usable];" array follows:
        see the DK_ENTRIES() macro */
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index ddd0582..0768d11 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -300,7 +300,7 @@ PyDict_Fini(void)
             2 : sizeof(int32_t))
 #endif
 #define DK_ENTRIES(dk) \
-    ((PyDictKeyEntry*)(&(dk)->dk_indices.as_1[DK_SIZE(dk) * DK_IXSIZE(dk)]))
+    ((PyDictKeyEntry*)(&((int8_t*)((dk)->dk_indices))[DK_SIZE(dk) * DK_IXSIZE(dk)]))
 
 #define DK_DEBUG_INCREF _Py_INC_REFTOTAL _Py_REF_DEBUG_COMMA
 #define DK_DEBUG_DECREF _Py_DEC_REFTOTAL _Py_REF_DEBUG_COMMA
@@ -318,21 +318,21 @@ dk_get_index(PyDictKeysObject *keys, Py_ssize_t i)
     Py_ssize_t ix;
 
     if (s <= 0xff) {
-        int8_t *indices = keys->dk_indices.as_1;
+        int8_t *indices = (int8_t*)(keys->dk_indices);
         ix = indices[i];
     }
     else if (s <= 0xffff) {
-        int16_t *indices = keys->dk_indices.as_2;
+        int16_t *indices = (int16_t*)(keys->dk_indices);
         ix = indices[i];
     }
 #if SIZEOF_VOID_P > 4
     else if (s > 0xffffffff) {
-        int64_t *indices = keys->dk_indices.as_8;
+        int64_t *indices = (int64_t*)(keys->dk_indices);
         ix = indices[i];
     }
 #endif
     else {
-        int32_t *indices = keys->dk_indices.as_4;
+        int32_t *indices = (int32_t*)(keys->dk_indices);
         ix = indices[i];
     }
     assert(ix >= DKIX_DUMMY);
@@ -348,23 +348,23 @@ dk_set_index(PyDictKeysObject *keys, Py_ssize_t i, Py_ssize_t ix)
     assert(ix >= DKIX_DUMMY);
 
     if (s <= 0xff) {
-        int8_t *indices = keys->dk_indices.as_1;
+        int8_t *indices = (int8_t*)(keys->dk_indices);
         assert(ix <= 0x7f);
         indices[i] = (char)ix;
     }
     else if (s <= 0xffff) {
-        int16_t *indices = keys->dk_indices.as_2;
+        int16_t *indices = (int16_t*)(keys->dk_indices);
         assert(ix <= 0x7fff);
         indices[i] = (int16_t)ix;
     }
 #if SIZEOF_VOID_P > 4
     else if (s > 0xffffffff) {
-        int64_t *indices = keys->dk_indices.as_8;
+        int64_t *indices = (int64_t*)(keys->dk_indices);
         indices[i] = ix;
     }
 #endif
     else {
-        int32_t *indices = keys->dk_indices.as_4;
+        int32_t *indices = (int32_t*)(keys->dk_indices);
         assert(ix <= 0x7fffffff);
         indices[i] = (int32_t)ix;
     }
@@ -424,8 +424,8 @@ static PyDictKeysObject empty_keys_struct = {
         lookdict_split, /* dk_lookup */
         0, /* dk_usable (immutable) */
         0, /* dk_nentries */
-        .dk_indices = { .as_1 = {DKIX_EMPTY, DKIX_EMPTY, DKIX_EMPTY, DKIX_EMPTY,
-                                 DKIX_EMPTY, DKIX_EMPTY, DKIX_EMPTY, DKIX_EMPTY}},
+        {DKIX_EMPTY, DKIX_EMPTY, DKIX_EMPTY, DKIX_EMPTY,
+         DKIX_EMPTY, DKIX_EMPTY, DKIX_EMPTY, DKIX_EMPTY}, /* dk_indices */
 };
 
 static PyObject *empty_values[1] = { NULL };
@@ -533,7 +533,6 @@ static PyDictKeysObject *new_keys_object(Py_ssize_t size)
     }
     else {
         dk = PyObject_MALLOC(sizeof(PyDictKeysObject)
-                             - Py_MEMBER_SIZE(PyDictKeysObject, dk_indices)
                              + es * size
                              + sizeof(PyDictKeyEntry) * usable);
         if (dk == NULL) {
@@ -546,7 +545,7 @@ static PyDictKeysObject *new_keys_object(Py_ssize_t size)
     dk->dk_usable = usable;
     dk->dk_lookup = lookdict_unicode_nodummy;
     dk->dk_nentries = 0;
-    memset(&dk->dk_indices.as_1[0], 0xff, es * size);
+    memset(&dk->dk_indices[0], 0xff, es * size);
     memset(DK_ENTRIES(dk), 0, sizeof(PyDictKeyEntry) * usable);
     return dk;
 }
@@ -3086,7 +3085,6 @@ _PyDict_SizeOf(PyDictObject *mp)
        in the type object. */
     if (mp->ma_keys->dk_refcnt == 1)
         res += (sizeof(PyDictKeysObject)
-                - Py_MEMBER_SIZE(PyDictKeysObject, dk_indices)
                 + DK_IXSIZE(mp->ma_keys) * size
                 + sizeof(PyDictKeyEntry) * usable);
     return res;
@@ -3096,7 +3094,6 @@ Py_ssize_t
 _PyDict_KeysSize(PyDictKeysObject *keys)
 {
     return (sizeof(PyDictKeysObject)
-            - Py_MEMBER_SIZE(PyDictKeysObject, dk_indices)
             + DK_IXSIZE(keys) * DK_SIZE(keys)
             + USABLE_FRACTION(DK_SIZE(keys)) * sizeof(PyDictKeyEntry));
 }
diff --git a/Tools/gdb/libpython.py b/Tools/gdb/libpython.py
index 6d7a942..6d3d52f 100755
--- a/Tools/gdb/libpython.py
+++ b/Tools/gdb/libpython.py
@@ -736,7 +736,7 @@ class PyDictObjectPtr(PyObjectPtr):
         else:
             offset = 8 * dk_size
 
-        ent_addr = keys['dk_indices']['as_1'].address
+        ent_addr = keys['dk_indices'].address
         ent_addr = ent_addr.cast(_type_unsigned_char_ptr()) + offset
         ent_ptr_t = gdb.lookup_type('PyDictKeyEntry').pointer()
         ent_addr = ent_addr.cast(ent_ptr_t)