https://bugs.gentoo.org/771765
https://sourceware.org/PR27397

On i586-like CPUs endbr32 added by -Wl,-z,ibt,-z,shstk
generates crashing binaries and causes ./configure failure.

From 847e4b3207f97762dc641db8d3b188081c3370c3 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Fri, 12 Feb 2021 16:30:23 -0800
Subject: [PATCH] GCC_CET_HOST_FLAGS: Check if host supports multi-byte NOPs

---
 config/cet.m4       | 19 ++++++++++++++++---
 libiberty/configure | 29 +++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/config/cet.m4 b/config/cet.m4
index c67fb4f35b6..7718be1afe8 100644
--- a/config/cet.m4
+++ b/config/cet.m4
@@ -130,6 +130,18 @@ fi
 if test x$may_have_cet = xyes; then
   if test x$cross_compiling = xno; then
     AC_TRY_RUN([
+int
+main ()
+{
+  asm ("endbr32");
+  return 0;
+}
+    ],
+    [have_multi_byte_nop=yes],
+    [have_multi_byte_nop=no])
+    have_cet=no
+    if test x$have_multi_byte_nop = xyes; then
+      AC_TRY_RUN([
 static void
 foo (void)
 {
@@ -155,9 +167,10 @@ main ()
   bar ();
   return 0;
 }
-    ],
-    [have_cet=no],
-    [have_cet=yes])
+      ],
+      [have_cet=no],
+      [have_cet=yes])
+    fi
     if test x$enable_cet = xno -a x$have_cet = xyes; then
       AC_MSG_ERROR([Intel CET must be enabled on Intel CET enabled host])
     fi
diff --git a/libiberty/configure b/libiberty/configure
index 160b8c9e8b1..29a690d44fc 100755
--- a/libiberty/configure
+++ b/libiberty/configure
@@ -5539,6 +5539,34 @@ else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+int
+main ()
+{
+  asm ("endbr32");
+  return 0;
+}
+
+_ACEOF
+if ac_fn_c_try_run "$LINENO"; then :
+  have_multi_byte_nop=yes
+else
+  have_multi_byte_nop=no
+fi
+rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext \
+  conftest.$ac_objext conftest.beam conftest.$ac_ext
+fi
+
+    have_cet=no
+    if test x$have_multi_byte_nop = xyes; then
+      if test "$cross_compiling" = yes; then :
+  { { $as_echo "$as_me:${as_lineno-$LINENO}: error: in \`$ac_pwd':" >&5
+$as_echo "$as_me: error: in \`$ac_pwd':" >&2;}
+as_fn_error $? "cannot run test program while cross compiling
+See \`config.log' for more details" "$LINENO" 5; }
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
 static void
 foo (void)
 {
@@ -5575,6 +5603,7 @@ rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext \
   conftest.$ac_objext conftest.beam conftest.$ac_ext
 fi
 
+    fi
     if test x$enable_cet = xno -a x$have_cet = xyes; then
       as_fn_error $? "Intel CET must be enabled on Intel CET enabled host" "$LINENO" 5
     fi
-- 
2.29.2