i386: Fail if configured with --enable-cet

Since it is only supported for x86_64.

Checked on i686-linux-gnu.

INSTALL

@@ -147,8 +147,7 @@ if ‘CFLAGS’ is specified it must enable optimization.  For example:
      ‘--enable-cet=permissive’, CET is disabled when dlopening a non CET
      enabled shared library in CET enabled application.
 
-     NOTE: ‘--enable-cet’ has been tested for x86_64 and x32 on non-CET
-     and CET processors.
+     NOTE: ‘--enable-cet’ is only supported on x86_64 and x32.
 
 ‘--enable-memory-tagging’
      Enable memory tagging support if the architecture supports it.

NEWS

@@ -9,8 +9,8 @@ Version 2.39
 
 Major new features:
 
-* Sync with Linux kernel 6.6 shadow stack interface.  Since only x86-64
-  is supported, --enable-cet is ignored for i386.
+* Sync with Linux kernel 6.6 shadow stack interface.  The --enable-cet
+  configure option in only supported on x86-64.
 
 * struct statvfs now has an f_type member, equal to the f_type statfs member;
   on the Hurd this was always available under a reserved name,

manual/install.texi

@@ -175,8 +175,7 @@ enabled shared library in CET enabled application.  With
 @option{--enable-cet=permissive}, CET is disabled when dlopening a
 non CET enabled shared library in CET enabled application.
 
-NOTE: @option{--enable-cet} has been tested for x86_64 and x32
-on non-CET and CET processors.
+NOTE: @option{--enable-cet} is only supported on x86_64 and x32.
 
 @item --enable-memory-tagging
 Enable memory tagging support if the architecture supports it.  When

sysdeps/i386/configure

@@ -1,10 +1,10 @@
 # This file is generated from configure.ac by Autoconf.  DO NOT EDIT!
  # Local configure fragment for sysdeps/i386.
 
-# CET is only supported for x86-64.  Set enable-cet to "no" to allow
-# "ifneq ($(enable-cet),no)" in x86 Makefiles.
-config_vars="$config_vars
-enable-cet = "no""
+# CET is only supported for x86-64.
+if test $enable_cet != no; then
+  as_fn_error $? "\"CET is only supported on x86_64 or x32\"" "$LINENO" 5
+fi
 
 # We no longer support i386 since it lacks the atomic instructions
 # required to implement NPTL threading.

sysdeps/i386/configure.ac

@@ -1,9 +1,10 @@
 GLIBC_PROVIDES dnl See aclocal.m4 in the top level source directory.
 # Local configure fragment for sysdeps/i386.
 
-# CET is only supported for x86-64.  Set enable-cet to "no" to allow
-# "ifneq ($(enable-cet),no)" in x86 Makefiles.
-LIBC_CONFIG_VAR([enable-cet], ["no"])
+# CET is only supported for x86-64.
+if test $enable_cet != no; then
+  AC_MSG_ERROR(["CET is only supported on x86_64 or x32"])
+fi
 
 # We no longer support i386 since it lacks the atomic instructions
 # required to implement NPTL threading.