config: Allow memory tagging to be enabled when configuring glibc

This patch adds the configuration machinery to allow memory tagging to be
enabled from the command line via the configure option --enable-memory-tagging.

The current default is off, though in time we may change that once the API
is more stable.

INSTALL

@@ -142,6 +142,20 @@ if 'CFLAGS' is specified it must enable optimization.  For example:
      non-CET processors.  '--enable-cet' has been tested for i686,
      x86_64 and x32 on CET processors.
 
+'--enable-memory-tagging'
+     Enable memory tagging support if the architecture supports it.
+     When the GNU C Library is built with this option then the resulting
+     library will be able to control the use of tagged memory when
+     hardware support is present by use of the tunable
+     'glibc.mem.tagging'.  This includes the generation of tagged memory
+     when using the 'malloc' APIs.
+
+     At present only AArch64 platforms with MTE provide this
+     functionality, although the library will still operate (without
+     memory tagging) on older versions of the architecture.
+
+     The default is to disable support for memory tagging.
+
 '--disable-profile'
      Don't build libraries with profiling information.  You may want to
      use this option if you don't plan to do profiling.

config.h.in

@@ -160,6 +160,9 @@
 /* Define if __stack_chk_guard canary should be randomized at program startup.  */
 #undef ENABLE_STACKGUARD_RANDOMIZE
 
+/* Define if memory tagging support should be enabled.  */
+#undef USE_MTAG
+
 /* Package description.  */
 #undef PKGVERSION
 

config.make.in

@@ -84,6 +84,8 @@ mach-interface-list = @mach_interface_list@
 
 experimental-malloc = @experimental_malloc@
 
+memory-tagging = @memory_tagging@
+
 nss-crypt = @libc_cv_nss_crypt@
 static-nss-crypt = @libc_cv_static_nss_crypt@
 

configure

@@ -676,6 +676,7 @@ build_nscd
 libc_cv_static_nss_crypt
 libc_cv_nss_crypt
 build_crypt
+memory_tagging
 experimental_malloc
 enable_werror
 all_warnings
@@ -781,6 +782,7 @@ enable_all_warnings
 enable_werror
 enable_multi_arch
 enable_experimental_malloc
+enable_memory_tagging
 enable_crypt
 enable_nss_crypt
 enable_systemtap
@@ -1450,6 +1452,8 @@ Optional Features:
                           architectures
   --disable-experimental-malloc
                           disable experimental malloc features
+  --enable-memory-tagging enable memory tagging if supported by the
+                          architecture [default=no]
   --disable-crypt         do not build nor install the passphrase hashing
                           library, libcrypt
   --enable-nss-crypt      enable libcrypt to use nss
@@ -3519,6 +3523,24 @@ fi
 
 
 
+# Check whether --enable-memory-tagging was given.
+if test "${enable_memory_tagging+set}" = set; then :
+  enableval=$enable_memory_tagging; memory_tagging=$enableval
+else
+  memory_tagging=no
+fi
+
+if test "$memory_tagging" = yes; then
+  # Only enable this on architectures that support it.
+  case $host_cpu in
+    aarch64)
+      $as_echo "#define USE_MTAG 1" >>confdefs.h
+
+      ;;
+  esac
+fi
+
+
 # Check whether --enable-crypt was given.
 if test "${enable_crypt+set}" = set; then :
   enableval=$enable_crypt; build_crypt=$enableval

configure.ac

@@ -311,6 +311,21 @@ AC_ARG_ENABLE([experimental-malloc],
 	      [experimental_malloc=yes])
 AC_SUBST(experimental_malloc)
 
+AC_ARG_ENABLE([memory-tagging],
+	      AC_HELP_STRING([--enable-memory-tagging],
+			     [enable memory tagging if supported by the architecture @<:@default=no@:>@]),
+	      [memory_tagging=$enableval],
+	      [memory_tagging=no])
+if test "$memory_tagging" = yes; then
+  # Only enable this on architectures that support it.
+  case $host_cpu in
+    aarch64)
+      AC_DEFINE(USE_MTAG)
+      ;;
+  esac
+fi
+AC_SUBST(memory_tagging)
+
 AC_ARG_ENABLE([crypt],
               AC_HELP_STRING([--disable-crypt],
                              [do not build nor install the passphrase hashing library, libcrypt]),

manual/install.texi

@@ -171,6 +171,19 @@ NOTE: @option{--enable-cet} has been tested for i686, x86_64 and x32
 on non-CET processors.  @option{--enable-cet} has been tested for
 i686, x86_64 and x32 on CET processors.
 
+@item --enable-memory-tagging
+Enable memory tagging support if the architecture supports it.  When
+@theglibc{} is built with this option then the resulting library will
+be able to control the use of tagged memory when hardware support is
+present by use of the tunable @samp{glibc.mem.tagging}.  This includes
+the generation of tagged memory when using the @code{malloc} APIs.
+
+At present only AArch64 platforms with MTE provide this functionality,
+although the library will still operate (without memory tagging) on
+older versions of the architecture.
+
+The default is to disable support for memory tagging.
+
 @item --disable-profile
 Don't build libraries with profiling information.  You may want to use
 this option if you don't plan to do profiling.