xml: fix statically-allocated opaque backend info array

It was sized for 64bit pointers max, it's not enough on 128bits platforms
such as Capability Hardware Enhanced RISC Instructions (CHERI).

Use something a bit more generic but still a bit hardwired to keep
things simple and statically allocatable on the stack.

Thanks to Jeff Hammond for the report.

Signed-off-by: Brice Goglin <[email protected]>

Author: bgoglin

include/private/xml.h

@@ -24,8 +24,9 @@ typedef struct hwloc__xml_import_state_s {
 
   /* opaque data used to store backend-specific data.
    * statically allocated to allow stack-allocation by the common code without knowing actual backend needs.
+   * libxml is 3 ptrs. nolibxml is 3 ptr + one int.
    */
-  char data[32];
+  char data[4 * SIZEOF_VOID_P];
 } * hwloc__xml_import_state_t;
 
 HWLOC_DECLSPEC int hwloc__xml_import_diff(hwloc__xml_import_state_t state, hwloc_topology_diff_t *firstdiffp);
@@ -65,8 +66,9 @@ typedef struct hwloc__xml_export_state_s {
 
   /* opaque data used to store backend-specific data.
    * statically allocated to allow stack-allocation by the common code without knowing actual backend needs.
+   * libxml is 1 ptr. nolibxml is 1 ptr + 2 size_t + 3 ints.
    */
-  char data[40];
+  char data[6 * SIZEOF_VOID_P];
 } * hwloc__xml_export_state_t;
 
 HWLOC_DECLSPEC void hwloc__xml_export_topology(hwloc__xml_export_state_t parentstate, hwloc_topology_t topology, unsigned long flags);