Adding upstream version 15.4.upstream/15.4upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/src/common/link-canary.c b/src/common/link-canary.c
new file mode 100644
index 0000000..97105ef
--- /dev/null
+++ b/src/common/link-canary.c
@@ -0,0 +1,36 @@
+/*-------------------------------------------------------------------------
+ * link-canary.c
+ *	  Detect whether src/common functions came from frontend or backend.
+ *
+ * Copyright (c) 2018-2022, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/common/link-canary.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "c.h"
+
+#include "common/link-canary.h"
+
+/*
+ * This function just reports whether this file was compiled for frontend
+ * or backend environment.  We need this because in some systems, mainly
+ * ELF-based platforms, it is possible for a shlib (such as libpq) loaded
+ * into the backend to call a backend function named XYZ in preference to
+ * the shlib's own function XYZ.  That's bad if the two functions don't
+ * act identically.  This exact situation comes up for many functions in
+ * src/common and src/port, where the same function names exist in both
+ * libpq and the backend but they don't act quite identically.  To verify
+ * that appropriate measures have been taken to prevent incorrect symbol
+ * resolution, libpq should test that this function returns true.
+ */
+bool
+pg_link_canary_is_frontend(void)
+{
+#ifdef FRONTEND
+	return true;
+#else
+	return false;
+#endif
+}