[res] Add named padding to ResTable_config

Follow the way the structs are defined in this file and
explicitly pad the structure with a named field.

+ add some static_assert statements to make sure nothing
  accidentally breaks binary structure of configs.

Test: build + boot
Flag: EXEMPT minor refactoring
Change-Id: I7e93aa0e92b080d0dcb77c790e5341f2342d7d2d

1 files changed, 10 insertions, 0 deletions

diff --git a/libs/androidfw/include/androidfw/ResourceTypes.h b/libs/androidfw/include/androidfw/ResourceTypes.h
index 30594dcfa939..0d45149267cf 100644
--- a/libs/androidfw/include/androidfw/ResourceTypes.h
+++ b/libs/androidfw/include/androidfw/ResourceTypes.h
@@ -1265,6 +1265,9 @@ struct ResTable_config
     // Varies in length from 3 to 8 chars. Zero-filled value.
     char localeNumberingSystem[8];
 
+    // Mark all padding explicitly so it's clear how much we can expand it.
+    char endPadding[3];
+
     void copyFromDeviceNoSwap(const ResTable_config& o) {
       const auto o_size = dtohl(o.size);
       if (o_size >= sizeof(ResTable_config)) [[likely]] {
@@ -1422,6 +1425,13 @@ struct ResTable_config
     void swapHtoD_slow();
 };
 
+// Fix the struct size for backward compatibility
+static_assert(sizeof(ResTable_config) == 64);
+
+// Make sure there's no unaccounted padding in the structure.
+static_assert(offsetof(ResTable_config, endPadding) +
+                  sizeof(ResTable_config::endPadding) == sizeof(ResTable_config));
+
 /**
  * A specification of the resources defined by a particular type.
  *