Commit c8b4edf3d0b8903cabf8ae1bc71c310d880160e1
2021-07-29T17:53:10
Fix SDL_Event definition to support systems with pointers larger than 8 bytes This is needed to support CHERI, and thus Arm's experimental Morello prototype, where pointers are implemented using unforgeable capabilities that include bounds and permissions metadata to provide fine-grained spatial and referential memory safety, as well as revocation by sweeping memory to provide heap temporal memory safety.
diff --git a/include/SDL_events.h b/include/SDL_events.h
index 6cdb662..c3037b2 100644
--- a/include/SDL_events.h
+++ b/include/SDL_events.h
@@ -620,18 +620,24 @@ typedef union SDL_Event
SDL_DollarGestureEvent dgesture; /**< Gesture event data */
SDL_DropEvent drop; /**< Drag and drop event data */
- /* This is necessary for ABI compatibility between Visual C++ and GCC
- Visual C++ will respect the push pack pragma and use 52 bytes for
- this structure, and GCC will use the alignment of the largest datatype
- within the union, which is 8 bytes.
+ /* This is necessary for ABI compatibility between Visual C++ and GCC.
+ Visual C++ will respect the push pack pragma and use 52 bytes (size of
+ SDL_TextEditingEvent, the largest structure for 32-bit and 64-bit
+ architectures) for this union, and GCC will use the alignment of the
+ largest datatype within the union, which is 8 bytes on 64-bit
+ architectures.
So... we'll add padding to force the size to be 56 bytes for both.
+
+ On architectures where pointers are 16 bytes, this needs rounding up to
+ the next multiple of 16, 64, and on architectures where pointers are
+ even larger the size of SDL_UserEvent will dominate as being 3 pointers.
*/
- Uint8 padding[56];
+ Uint8 padding[sizeof(void *) <= 8 ? 56 : sizeof(void *) == 16 ? 64 : 3 * sizeof(void *)];
} SDL_Event;
/* Make sure we haven't broken binary compatibility */
-SDL_COMPILE_TIME_ASSERT(SDL_Event, sizeof(SDL_Event) == 56);
+SDL_COMPILE_TIME_ASSERT(SDL_Event, sizeof(SDL_Event) == sizeof(((SDL_Event *)NULL)->padding));
/* Function prototypes */