+
+/*
+ * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63293
+ */
+# ifdef __aarch64__
+# if GCC_VERSION < 50100
+# error Your gcc version performs unsafe access to deallocated stack
+# endif
+# endif
+
+#endif
+
+/*
+ * READ/WRITE_ONCE were introduced in kernel 3.19 and ACCESS_ONCE
+ * was removed in 4.15. Prefer READ/WRITE but fallback to ACCESS
+ * when they are not available.
+ */
+#ifndef READ_ONCE
+# define READ_ONCE(x) ACCESS_ONCE(x)
+#endif
+
+#ifndef WRITE_ONCE
+# define WRITE_ONCE(x, val) ({ ACCESS_ONCE(x) = val; })
+#endif
+
+/*
+ * In v4.15 a smp read barrier was added to READ_ONCE to replace
+ * lockless_dereference(), replicate this behavior on prior kernels
+ * and remove calls to smp_read_barrier_depends which was dropped
+ * in v5.9.
+ */
+#if (LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(4,15,0))
+#define LTTNG_READ_ONCE(x) READ_ONCE(x)
+#else
+#define LTTNG_READ_ONCE(x) \
+({ \
+ typeof(x) __val = READ_ONCE(x); \
+ smp_read_barrier_depends(); \
+ __val; \
+})