Allow the use of readlinkat over readlink.

This can be useful in situations where readlink is disallowed.

configure.ac

@@ -1277,6 +1277,22 @@ if test "x$enable_log" = "x1" ; then
 fi
 AC_SUBST([enable_log])
 
+dnl Do not use readlinkat by default
+AC_ARG_ENABLE([readlinkat],
+  [AS_HELP_STRING([--enable-readlinkat], [Use readlinkat over readlink])],
+[if test "x$enable_readlinkat" = "xno" ; then
+  enable_readlinkat="0"
+else
+  enable_readlinkat="1"
+fi
+],
+[enable_readlinkat="0"]
+)
+if test "x$enable_readlinkat" = "x1" ; then
+  AC_DEFINE([JEMALLOC_READLINKAT], [ ])
+fi
+AC_SUBST([enable_readlinkat])
+
 
 JE_COMPILABLE([a program using __builtin_unreachable], [
 void foo (void) {

include/jemalloc/internal/jemalloc_internal_defs.h.in

@@ -245,6 +245,12 @@
  */
 #undef JEMALLOC_LOG
 
+/*
+ * If defined, use readlinkat() (instead of readlink()) to follow
+ * /etc/malloc_conf.
+ */
+#undef JEMALLOC_READLINKAT
+
 /*
  * Darwin (OS X) uses zones to work around Mach-O symbol override shortcomings.
  */

src/jemalloc.c

@@ -961,7 +961,12 @@ malloc_conf_init(sc_data_t *sc_data) {
 			 * Try to use the contents of the "/etc/malloc.conf"
 			 * symbolic link's name.
 			 */
+#ifndef JEMALLOC_READLINKAT
 			linklen = readlink(linkname, buf, sizeof(buf) - 1);
+#else
+			linklen = readlinkat(AT_FDCWD, linkname, buf,
+			    sizeof(buf) - 1);
+#endif
 			if (linklen == -1) {
 				/* No configuration specified. */
 				linklen = 0;