Default to --with-default-link=yes if configure check finds good -shared layout.

3 files changed, 124 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 61524ed..5a440ae 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2011-07-02  Roland McGrath  <roland@hack.frob.com>
 
+	* configure.in (use-default-link): Default to yes if a test -shared
+	link meets our qualifications.
+	* configure: Regenerated.
+
 	* config.make.in (output-format): New variable.
 	* configure.in: Check for ld --print-output-format support.
 	* configure: Regenerated.
diff --git a/configure b/configure
index 55a4b30..2bea3c0 100755
--- a/configure
+++ b/configure
@@ -1469,7 +1469,7 @@ Optional Packages:
   --without-cvs           if CVS should not be used
   --with-headers=PATH     location of system headers to use (for example
                           /usr/src/linux/include) [default=compiler default]
-  --with-default-link     do not use explicit linker scripts [default=no]
+  --with-default-link     do not use explicit linker scripts
   --with-tls              enable support for TLS
   --without-__thread      do not use TLS features even when supporting them
   --with-cpu=CPU          select code for CPU variant
@@ -3593,7 +3593,7 @@ fi
 if test "${with_default_link+set}" = set; then :
   withval=$with_default_link; use_default_link=$withval
 else
-  use_default_link=no
+  use_default_link=default
 fi
 
 
@@ -6702,6 +6702,69 @@ fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_hashstyle" >&5
 $as_echo "$libc_cv_hashstyle" >&6; }
 
+
+  # The linker's default -shared behavior is good enough if it
+  # does these things that our custom linker scripts ensure that
+  # all allocated NOTE sections come first.
+  if test "$use_default_link" = default; then
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking for sufficient default -shared layout" >&5
+$as_echo_n "checking for sufficient default -shared layout... " >&6; }
+if ${libc_cv_use_default_link+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+      libc_cv_use_default_link=no
+    cat > conftest.s <<\EOF
+	  .section .note.a,"a",%note
+	  .balign 4
+	  .long 4,4,9
+	  .string "GNU"
+	  .string "foo"
+	  .section .note.b,"a",%note
+	  .balign 4
+	  .long 4,4,9
+	  .string "GNU"
+	  .string "bar"
+EOF
+    if { ac_try='  ${CC-cc} $ASFLAGS -shared -o conftest.so conftest.s 1>&5'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; } &&
+       ac_try=`$READELF -S conftest.so | sed -n \
+	 '${x;p;}
+	  s/^ *\[ *[1-9][0-9]*\]  *\([^ ][^ ]*\)  *\([^ ][^ ]*\) .*$/\2 \1/
+	  t a
+	  b
+	  : a
+	  H'`
+    then
+      libc_seen_a=no libc_seen_b=no
+      set -- $ac_try
+      while test $# -ge 2 -a "$1" = NOTE; do
+	case "$2" in
+	.note.a) libc_seen_a=yes ;;
+	.note.b) libc_seen_b=yes ;;
+	esac
+	shift 2
+      done
+      case "$libc_seen_a$libc_seen_b" in
+      yesyes)
+	libc_cv_use_default_link=yes
+	;;
+      *)
+	echo >&5 "\
+$libc_seen_a$libc_seen_b from:
+$ac_try"
+	;;
+      esac
+    fi
+    rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_use_default_link" >&5
+$as_echo "$libc_cv_use_default_link" >&6; }
+    use_default_link=$libc_cv_use_default_link
+  fi
 fi
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking linker output format" >&5
diff --git a/configure.in b/configure.in
index a28cd70..65ace27 100644
--- a/configure.in
+++ b/configure.in
@@ -117,10 +117,9 @@ AC_ARG_WITH([headers],
 AC_SUBST(use_default_link)
 AC_ARG_WITH([default-link],
 	    AC_HELP_STRING([--with-default-link],
-			   [do not use explicit linker scripts
-			    @<:@default=no@:>@]),
+			   [do not use explicit linker scripts]),
 	    [use_default_link=$withval],
-	    [use_default_link=no])
+	    [use_default_link=default])
 
 AC_ARG_ENABLE([sanity-checks],
 	      AC_HELP_STRING([--disable-sanity-checks],
@@ -1801,6 +1800,59 @@ EOF
   fi
   rm -f conftest*])
   AC_SUBST(libc_cv_hashstyle)
+
+  # The linker's default -shared behavior is good enough if it
+  # does these things that our custom linker scripts ensure that
+  # all allocated NOTE sections come first.
+  if test "$use_default_link" = default; then
+    AC_CACHE_CHECK([for sufficient default -shared layout],
+		   libc_cv_use_default_link, [dnl
+    libc_cv_use_default_link=no
+    cat > conftest.s <<\EOF
+	  .section .note.a,"a",%note
+	  .balign 4
+	  .long 4,4,9
+	  .string "GNU"
+	  .string "foo"
+	  .section .note.b,"a",%note
+	  .balign 4
+	  .long 4,4,9
+	  .string "GNU"
+	  .string "bar"
+EOF
+    if AC_TRY_COMMAND([dnl
+  ${CC-cc} $ASFLAGS -shared -o conftest.so conftest.s 1>&AS_MESSAGE_LOG_FD]) &&
+       ac_try=`$READELF -S conftest.so | sed -n \
+	 ['${x;p;}
+	  s/^ *\[ *[1-9][0-9]*\]  *\([^ ][^ ]*\)  *\([^ ][^ ]*\) .*$/\2 \1/
+	  t a
+	  b
+	  : a
+	  H']`
+    then
+      libc_seen_a=no libc_seen_b=no
+      set -- $ac_try
+      while test $# -ge 2 -a "$1" = NOTE; do
+	case "$2" in
+	.note.a) libc_seen_a=yes ;;
+	.note.b) libc_seen_b=yes ;;
+	esac
+	shift 2
+      done
+      case "$libc_seen_a$libc_seen_b" in
+      yesyes)
+	libc_cv_use_default_link=yes
+	;;
+      *)
+	echo >&AS_MESSAGE_LOG_FD "\
+$libc_seen_a$libc_seen_b from:
+$ac_try"
+	;;
+      esac
+    fi
+    rm -f conftest*])
+    use_default_link=$libc_cv_use_default_link
+  fi
 fi
 
 AC_CACHE_CHECK(linker output format, libc_cv_output_format, [dnl