From 9f917f7b411c307c34eb1bae85d72ffe26167523 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Tue, 3 Dec 2019 21:11:32 +0100
Subject: [PATCH] x86: Assume --enable-cet if GCC defaults to CET [BZ #25225]

This links in CET support if GCC defaults to CET.  Otherwise, __CET__
is defined, yet CET functionality is not compiled and linked into the
dynamic loader, resulting in a linker failure due to undefined
references to _dl_cet_check and _dl_open_check.

(cherry picked from commit 9fb8139079ef0bb1aa33a4ae418cbb113b9b9da7)
---
 NEWS         |  1 +
 configure    | 23 ++++++++++++++++++++++-
 configure.ac |  9 ++++++++-
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/configure b/configure
index fde57d63fe..c02753c0fe 100755
--- a/configure
+++ b/configure
@@ -3762,11 +3762,32 @@ else
 fi
 
 
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+#ifndef __CET__
+#error no CET compiler support
+#endif
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  libc_cv_compiler_default_cet=yes
+else
+  libc_cv_compiler_default_cet=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
 # Check whether --enable-cet was given.
 if test "${enable_cet+set}" = set; then :
   enableval=$enable_cet; enable_cet=$enableval
 else
-  enable_cet=no
+  enable_cet=$libc_cv_compiler_default_cet
 fi
 
 
diff --git a/configure.ac b/configure.ac
index 014e09a5d5..139554b94a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -464,11 +464,18 @@ AC_ARG_ENABLE([mathvec],
 	      [build_mathvec=$enableval],
 	      [build_mathvec=notset])
 
+AC_TRY_COMPILE([], [
+#ifndef __CET__
+# error no CET compiler support
+#endif],
+	       [libc_cv_compiler_default_cet=yes],
+	       [libc_cv_compiler_default_cet=no])
+
 AC_ARG_ENABLE([cet],
 	      AC_HELP_STRING([--enable-cet],
 			     [enable Intel Control-flow Enforcement Technology (CET), x86 only]),
 	      [enable_cet=$enableval],
-	      [enable_cet=no])
+	      [enable_cet=$libc_cv_compiler_default_cet])
 
 # We keep the original values in `$config_*' and never modify them, so we
 # can write them unchanged into config.make.  Everything else uses
-- 
2.20.1