[glibc/ibm/2.28/master] x86: Assume --enable-cet if GCC defaults to CET [BZ #25225]

[Tulio Magno Quites Machado Filho <tuliom@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9f917f7b411c307c34eb1bae85d72ffe26167523

commit 9f917f7b411c307c34eb1bae85d72ffe26167523
Author: Florian Weimer <fweimer@redhat.com>
Date:   Tue Dec 3 21:11:32 2019 +0100

    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)

Diff:
---
 NEWS         |  1 +
 configure    | 23 ++++++++++++++++++++++-
 configure.ac |  9 ++++++++-
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/NEWS b/NEWS
index 74efb0e..d488f14 100644
--- a/NEWS
+++ b/NEWS
@@ -71,6 +71,7 @@ The following bugs are resolved with this release:
   [24744] io: Remove the copy_file_range emulation.
   [25203] libio: Disable vtable validation for pre-2.1 interposed handles
   [25204] Ignore LD_PREFER_MAP_32BIT_EXEC for SUID programs
+  [25225] ld.so fails to link on x86 if GCC defaults to -fcf-protection
 
 Security related changes:
 
diff --git a/configure b/configure
index fde57d6..c02753c 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 014e09a..139554b 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