Z3 memory manager stores actual data along with its size, which causes the
memory to be 8-byte aligned. Use malloc non-portable functions to obtain
memory region size instead.

https://github.com/Z3Prover/z3/issues/6015

--- src/util/memory_manager.cpp.orig	2022-05-05 00:16:30 UTC
+++ src/util/memory_manager.cpp
@@ -13,6 +13,7 @@ --*/
 #include "util/error_codes.h"
 #include "util/debug.h"
 #include "util/scoped_timer.h"
+#include <malloc_np.h>
 // The following two function are automatically generated by the mk_make.py script.
 // The script collects ADD_INITIALIZER and ADD_FINALIZER commands in the .h files.
 // For example, rational.h contains
@@ -258,52 +259,43 @@ void memory::deallocate(void * p) {
 }
 
 void memory::deallocate(void * p) {
-    size_t * sz_p  = reinterpret_cast<size_t*>(p) - 1;
-    size_t sz      = *sz_p;
-    void * real_p  = reinterpret_cast<void*>(sz_p);
-    g_memory_thread_alloc_size -= sz;
-    free(real_p);
+    g_memory_thread_alloc_size -= malloc_usable_size(p);
+    if (g_memory_thread_alloc_size < 0) g_memory_thread_alloc_size = 0;
+    free(p);
     if (g_memory_thread_alloc_size < -SYNCH_THRESHOLD) {
         synchronize_counters(false);
     }
 }
 
 void * memory::allocate(size_t s) {
-    s = s + sizeof(size_t); // we allocate an extra field!
     void * r = malloc(s);
     if (r == 0) {
         throw_out_of_memory();
         return nullptr;
     }
-    *(static_cast<size_t*>(r)) = s;
     g_memory_thread_alloc_size += s;
     g_memory_thread_alloc_count += 1;
     if (g_memory_thread_alloc_size > SYNCH_THRESHOLD) {
         synchronize_counters(true);
     }
 
-    return static_cast<size_t*>(r) + 1; // we return a pointer to the location after the extra field
+    return r; // we return a pointer to the location after the extra field
 }
 
 void* memory::reallocate(void *p, size_t s) {
-    size_t *sz_p = reinterpret_cast<size_t*>(p)-1;
-    size_t sz = *sz_p;
-    void *real_p = reinterpret_cast<void*>(sz_p);
-    s = s + sizeof(size_t); // we allocate an extra field!
-
-    g_memory_thread_alloc_size += s - sz;
+    g_memory_thread_alloc_size += s - malloc_usable_size(p);
+    if (g_memory_thread_alloc_size < 0) g_memory_thread_alloc_size = 0;
     g_memory_thread_alloc_count += 1;
     if (g_memory_thread_alloc_size > SYNCH_THRESHOLD) {
         synchronize_counters(true);
     }
 
-    void *r = realloc(real_p, s);
+    void *r = realloc(p, s);
     if (r == 0) {
         throw_out_of_memory();
         return nullptr;
     }
-    *(static_cast<size_t*>(r)) = s;
-    return static_cast<size_t*>(r) + 1; // we return a pointer to the location after the extra field
+    return r;
 }
 
 #else