+
+/**
+ * Declare *allocx() and mallctl() as weak symbols. These will be provided by
+ * jemalloc if we are using jemalloc, or will be NULL if we are using another
+ * malloc implementation.
+ */
+extern "C" void* mallocx(size_t, int)
+__attribute__((__weak__));
+extern "C" void* rallocx(void*, size_t, int)
+__attribute__((__weak__));
+extern "C" size_t xallocx(void*, size_t, size_t, int)
+__attribute__((__weak__));
+extern "C" size_t sallocx(const void*, int)
+__attribute__((__weak__));
+extern "C" void dallocx(void*, int)
+__attribute__((__weak__));
+extern "C" size_t nallocx(size_t, int)
+__attribute__((__weak__));
+extern "C" int mallctl(const char*, void*, size_t*, void*, size_t)
+__attribute__((__weak__));
+
+#include <bits/functexcept.h>