libgcc: aarch64: Configure check for __getauxval

Add configure check for the __getauxval ABI symbol, which is always
available on aarch64 glibc, and may be available on other linux C
runtimes. For now only enabled on glibc, others have to override it

  target_configargs=libgcc_cv_have___getauxval=yes

This is deliberately obscure as it should be auto detected, ideally
via a feature test macro in unistd.h (link time detection is not
possible since the libc may not be installed at libgcc build time),
but currently there is no such feature test mechanism.

Without __getauxval, libgcc cannot do runtime CPU feature detection
and has to assume only the build time known features are available.

libgcc/ChangeLog:

	* config.in: Undef HAVE___GETAUXVAL.
	* configure: Regenerate.
	* configure.ac: Check for __getauxval.

3 files changed, 48 insertions, 0 deletions

diff --git a/libgcc/config.in b/libgcc/config.in
index 5dd96cd..441d4d3 100644
--- a/libgcc/config.in
+++ b/libgcc/config.in
@@ -16,6 +16,9 @@
 /* Define to 1 if the assembler supports .variant_pcs. */
 #undef HAVE_AS_VARIANT_PCS
 
+/* Define to 1 if __getauxval is available. */
+#undef HAVE___GETAUXVAL
+
 /* Define to 1 if the target assembler supports thread-local storage. */
 #undef HAVE_CC_TLS
 
diff --git a/libgcc/configure b/libgcc/configure
index 82c8558..3671d9b 100755
--- a/libgcc/configure
+++ b/libgcc/configure
@@ -5658,6 +5658,32 @@ $as_echo "#define HAVE_AS_VARIANT_PCS 1" >>confdefs.h
   ;;
 esac
 
+# Check __getauxval ABI symbol for CPU feature detection.
+case ${target} in
+aarch64*-linux-*)
+  # No link check because the libc may not be present.
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __getauxval" >&5
+$as_echo_n "checking for __getauxval... " >&6; }
+if ${libgcc_cv_have___getauxval+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  case ${target} in
+		  *-linux-gnu*)
+		    libgcc_cv_have___getauxval=yes
+		    ;;
+		  *)
+		    libgcc_cv_have___getauxval=no
+		  esac
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libgcc_cv_have___getauxval" >&5
+$as_echo "$libgcc_cv_have___getauxval" >&6; }
+  if test x$libgcc_cv_have___getauxval = xyes; then
+
+$as_echo "#define HAVE___GETAUXVAL 1" >>confdefs.h
+
+  fi
+esac
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for init priority support" >&5
 $as_echo_n "checking for init priority support... " >&6; }
 if ${libgcc_cv_init_priority+:} false; then :
diff --git a/libgcc/configure.ac b/libgcc/configure.ac
index fd0934c..467f5e6 100644
--- a/libgcc/configure.ac
+++ b/libgcc/configure.ac
@@ -665,6 +665,25 @@ aarch64*-*-*)
 esac])
 LIBGCC_CHECK_AS_VARIANT_PCS
 
+# Check __getauxval ABI symbol for CPU feature detection.
+case ${target} in
+aarch64*-linux-*)
+  # No link check because the libc may not be present.
+  AC_CACHE_CHECK([for __getauxval],
+		 [libgcc_cv_have___getauxval],
+		 [case ${target} in
+		  *-linux-gnu*)
+		    libgcc_cv_have___getauxval=yes
+		    ;;
+		  *)
+		    libgcc_cv_have___getauxval=no
+		  esac])
+  if test x$libgcc_cv_have___getauxval = xyes; then
+    AC_DEFINE(HAVE___GETAUXVAL, 1,
+	      [Define to 1 if __getauxval is available.])
+  fi
+esac
+
 dnl Check if as supports RTM instructions.
 AC_CACHE_CHECK(for init priority support, libgcc_cv_init_priority, [
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM(,