[Qemu-devel] [PATCH v7 12/31] qapi: Don't cast Enum* to int*

[Eric Blake <eblake@redhat.com>]

C compilers are allowed to represent enums as a smaller type
than int, if all enum values fit in the smaller type.  There
are even compiler flags that force the use of this smaller
representation, and using them changes the ABI of a binary.
Therefore, our generated code for visit_type_ENUM() (for all
qapi enums) was wrong for casting Enum* to int* when calling
visit_type_enum().

It appears that no one has been doing this for qemu, because
if they had, we are potentially dereferencing beyond bounds
or even risking a SIGBUS on platforms where unaligned pointer
dereferencing is fatal.  Better is to avoid the practice
entirely, and just use the correct types.

This matches the fix for alternate qapi types, done earlier in
"qapi: Simplify visiting of alternate types".

Signed-off-by: Eric Blake <eblake@redhat.com>

---
v7: rebase on typo fix
v6: new patch
---
 scripts/qapi-visit.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index 4a4f67d..6bd188b 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -178,12 +178,13 @@ out:


 def gen_visit_enum(name):
-    # FIXME cast from enum *obj to int * invalidly assumes enum is int
     return mcgen('''

 void visit_type_%(c_name)s(Visitor *v, %(c_name)s *obj, const char *name, Error **errp)
 {
-    visit_type_enum(v, (int *)obj, %(c_name)s_lookup, "%(name)s", name, errp);
+    int tmp = *obj;
+    visit_type_enum(v, &tmp, %(c_name)s_lookup, "%(name)s", name, errp);
+    *obj = tmp;
 }
 ''',
                  c_name=c_name(name), name=name)
-- 
2.4.3