Packing with n>1 must be considered for nested structs

Author: tautschnig

regression/ansi-c/Struct_Padding6/main.c

@@ -0,0 +1,32 @@
+#define STATIC_ASSERT(condition) \
+  int some_array##__LINE__[(condition) ? 1 : -1]
+
+#pragma pack(4)
+
+typedef unsigned short domid_t;
+typedef unsigned evtchn_port_t;
+struct evtchn_status {
+    domid_t dom;
+    evtchn_port_t port;
+    unsigned status;
+    unsigned vcpu;
+    union {
+        struct {
+            domid_t dom;
+        } unbound;
+        struct {
+            domid_t dom;
+            evtchn_port_t port;
+        } interdomain;
+        unsigned pirq;
+        unsigned virq;
+    } u;
+    char a;
+};
+
+int main()
+{
+  STATIC_ASSERT(__builtin_offsetof(struct evtchn_status,u.interdomain.port)==20);
+  STATIC_ASSERT(sizeof(struct evtchn_status)==28);
+  return 0;
+};

regression/ansi-c/Struct_Padding6/test.desc

@@ -0,0 +1,8 @@
+CORE
+main.c
+
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring
+^CONVERSION ERROR$

src/ansi-c/padding.cpp

@@ -188,8 +188,9 @@ void add_padding(struct_typet &type, const namespacet &ns)
     }  
   }
 
-  // Is the struct packed?
-  if(type.get_bool(ID_C_packed))
+  // Is the struct packed, without any alignment specification?
+  if(type.get_bool(ID_C_packed) &&
+     type.find(ID_C_alignment).is_nil())
     return; // done
 
   mp_integer offset=0;
@@ -291,6 +292,9 @@ void add_padding(struct_typet &type, const namespacet &ns)
         max_alignment=tmp_i;
     }
   }
+  // Is the struct packed, without any alignment specification?
+  else if(type.get_bool(ID_C_packed))
+    return; // done
 
   // There may be a need for 'end of struct' padding.
   // We use 'max_alignment'.