RFC: PR target/46770: Use .init_array/.fini_array sections

["H.J. Lu" <hongjiu dot lu at intel dot com>]

This patch uses .init_array/.fini_array sections instead of
.ctors/.dtors sections if mixing .init_array/.fini_array and
.ctors/.dtors sections with init_priority works.

It removes .ctors/.ctors sections from executables and DSOes, which will
remove one function call at startup time from each executable and DSO.
It should reduce image size and improve system startup time. 

If a platform with a working .init_array/.fini_array support needs a
different .init_array/.fini_array implementation, it can set
use_initfini_array to no.

Since .init_array/.fini_array is a target feature. --enable-initfini-array
is default to no unless the native run-time test is passed.

To pass the native run-time test, a linker with SORT_BY_INIT_PRIORITY
support is required.  The binutils patch is available at

http://sourceware.org/ml/binutils/2010-12/msg00466.html

This patch passed 32bit/64bit regression test on Linux/x86-64.  Any
comments?

Thanks.

H.J.
---
2010-12-14  H.J. Lu  <hongjiu.lu@intel.com>

	PR target/46770
	* acinclude.m4 (gcc_AC_INITFINI_ARRAY): Removed.

	* config.gcc (use_initfini_array): New variable.
	Use initfini-array.o if supported.

	* crtstuff.c: Don't generate .ctors nor .dtors sections if
	NO_CTORS_DTORS_SECTIONS is defined.

	* configure.ac: Remove gcc_AC_INITFINI_ARRAY.  Add
	--enable-initfini-array and check if .init_array can be used with
	.ctors.

	* configure: Regenerated.

	* config/initfini-array.c: New.
	* config/initfini-array.h: Likewise.
	* config/t-initfini-array: Likewise.

diff --git a/gcc/acinclude.m4 b/gcc/acinclude.m4
index 6f0f979..b0ab6d0 100644
--- a/gcc/acinclude.m4
+++ b/gcc/acinclude.m4
@@ -369,26 +369,6 @@ else
 fi
 fi])
 
-AC_DEFUN([gcc_AC_INITFINI_ARRAY],
-[AC_ARG_ENABLE(initfini-array,
-	[  --enable-initfini-array	use .init_array/.fini_array sections],
-	[], [
-AC_CACHE_CHECK(for .preinit_array/.init_array/.fini_array support,
-		 gcc_cv_initfini_array, [dnl
-  AC_RUN_IFELSE([AC_LANG_SOURCE([
-static int x = -1;
-int main (void) { return x; }
-int foo (void) { x = 0; }
-int (*fp) (void) __attribute__ ((section (".init_array"))) = foo;])],
-	     [gcc_cv_initfini_array=yes], [gcc_cv_initfini_array=no],
-	     [gcc_cv_initfini_array=no])])
-  enable_initfini_array=$gcc_cv_initfini_array
-])
-if test $enable_initfini_array = yes; then
-  AC_DEFINE(HAVE_INITFINI_ARRAY, 1,
-    [Define .init_array/.fini_array sections are available and working.])
-fi])
-
 dnl # _gcc_COMPUTE_GAS_VERSION
 dnl # Used by gcc_GAS_VERSION_GTE_IFELSE
 dnl #
diff --git a/gcc/config.gcc b/gcc/config.gcc
index 65cbf75..342bfa5 100644
--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -177,6 +177,9 @@
 #  configure_default_options
 #			Set to an initializer for configure_default_options
 #			in configargs.h, based on --with-cpu et cetera.
+#
+#  use_initfini_array	If set to yes, .init_array/.fini_array sections
+#			will be used if they work.
 
 # The following variables are used in each case-construct to build up the
 # outgoing variables:
@@ -219,6 +222,7 @@ default_gnu_indirect_function=no
 target_gtfiles=
 need_64bit_hwint=
 need_64bit_isa=
+use_initfini_array=yes
 
 # Don't carry these over build->host->target.  Please.
 xm_file=
@@ -3046,6 +3050,16 @@ if test x$with_schedule = x; then
 	esac
 fi
 
+# Support --enable-initfini-array.  Use initfini-array.h only if
+# use_initfini_array is also set to yes.  Some platforms don't need it
+# even if enable_initfini_array is yes.
+if test x$enable_initfini_array$use_initfini_array = xyesyes; then
+  tm_file="${tm_file} initfini-array.h"
+  tmake_file="${tmake_file} t-initfini-array"
+  extra_objs="$extra_objs initfini-array.o"
+  target_gtfiles="$target_gtfiles \$(srcdir)/config/initfini-array.c"
+fi
+
 # Validate and mark as valid any --with options supported
 # by this target.  In order to use a particular --with option
 # you must list it in supported_defaults; validating the value
diff --git a/gcc/config/initfini-array.c b/gcc/config/initfini-array.c
new file mode 100644
index 0000000..d5fd40f
--- /dev/null
+++ b/gcc/config/initfini-array.c
@@ -0,0 +1,79 @@
+/* Definitions for ELF systems with .init_array/.fini_array section
+   Copyright (C) 2010
+   Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "target.h"
+#include "output.h"
+#include "tree.h"
+#include "ggc.h"
+
+static GTY(()) section *init_array_section;
+static GTY(()) section *fini_array_section;
+
+void
+elf_initfini_array_init_sections (void)
+{
+  init_array_section = get_unnamed_section (0, output_section_asm_op,
+					    "\t.section\t.init_array");
+  fini_array_section = get_unnamed_section (0, output_section_asm_op,
+					    "\t.section\t.fini_array");
+}
+
+static section *
+get_elf_initfini_array_priority_section (int priority,
+					 bool constructor_p)
+{
+  section *sec;
+  if (priority != DEFAULT_INIT_PRIORITY)
+    {
+      char buf[18];
+      sprintf (buf, "%s.%.5u", 
+	       constructor_p ? ".init_array" : ".fini_array",
+	       priority);
+      sec = get_section (buf, SECTION_WRITE, NULL_TREE);
+    }
+  else
+    sec = constructor_p ? init_array_section : fini_array_section;
+  return sec;
+}
+
+/* Use .init_array section for constructors. */
+
+void
+elf_init_array_asm_out_constructor (rtx symbol, int priority)
+{
+  section *sec = get_elf_initfini_array_priority_section (priority,
+							  true);
+  assemble_addr_to_section (symbol, sec);
+}
+
+/* Use .fini_array section for destructors. */
+
+void
+elf_fini_array_asm_out_destructor (rtx symbol, int priority)
+{
+  section *sec = get_elf_initfini_array_priority_section (priority,
+							  false);
+  assemble_addr_to_section (symbol, sec);
+}
+
+#include "gt-initfini-array.h"
diff --git a/gcc/config/initfini-array.h b/gcc/config/initfini-array.h
new file mode 100644
index 0000000..b0b422a
--- /dev/null
+++ b/gcc/config/initfini-array.h
@@ -0,0 +1,46 @@
+/* Definitions for ELF systems with .init_array/.fini_array section
+   support.
+   Copyright (C) 2010
+   Free Software Foundation, Inc.
+
+   This file is part of GCC.
+
+   GCC is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published
+   by the Free Software Foundation; either version 3, or (at your
+   option) any later version.
+
+   GCC is distributed in the hope that it will be useful, but WITHOUT
+   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+   or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+   License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with GCC; see the file COPYING3.  If not see
+   <http://www.gnu.org/licenses/>.  */
+
+/* No need for .ctors/.dtors section since linker can place them in
+   .init_array/.fini_array section.  */
+#define NO_CTORS_DTORS_SECTIONS
+
+#undef INIT_SECTION_ASM_OP
+#undef FINI_SECTION_ASM_OP
+
+/* FIXME: INIT_ARRAY_SECTION_ASM_OP and FINI_ARRAY_SECTION_ASM_OP
+	  aren't used in any assembly codes.  But we have to define
+	  them to something.  */
+#define INIT_ARRAY_SECTION_ASM_OP Something
+#define FINI_ARRAY_SECTION_ASM_OP Something
+
+#ifndef TARGET_ASM_INIT_SECTIONS
+#define TARGET_ASM_INIT_SECTIONS elf_initfini_array_init_sections
+#endif
+extern void elf_initfini_array_init_sections (void);
+
+/* Use .init_array/.fini_array section for constructors and destructors. */
+#undef TARGET_ASM_CONSTRUCTOR
+#define TARGET_ASM_CONSTRUCTOR elf_init_array_asm_out_constructor
+#undef TARGET_ASM_DESTRUCTOR
+#define TARGET_ASM_DESTRUCTOR elf_fini_array_asm_out_destructor
+extern void elf_init_array_asm_out_constructor (rtx, int);
+extern void elf_fini_array_asm_out_destructor (rtx, int);
diff --git a/gcc/config/t-initfini-array b/gcc/config/t-initfini-array
new file mode 100644
index 0000000..3dcb25d
--- /dev/null
+++ b/gcc/config/t-initfini-array
@@ -0,0 +1,23 @@
+# Copyright (C) 2010
+# 2009 Free Software Foundation, Inc.
+#
+# This file is part of GCC.
+#
+# GCC is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3, or (at your option)
+# any later version.
+#
+# GCC is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with GCC; see the file COPYING3.  If not see
+# <http://www.gnu.org/licenses/>.
+
+initfini-array.o: $(srcdir)/config/initfini-array.c gt-initfini-array.h \
+	$(CONFIG_H) $(SYSTEM_H) coretypes.h $(TARGET_H) output.h \
+	$(TREE_H) $(GGC_H)
+	$(COMPILER) -c $(ALL_COMPILERFLAGS) $(ALL_CPPFLAGS) $(INCLUDES) $<
diff --git a/gcc/configure b/gcc/configure
index 9d76b41..a8cddf2 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -10442,6 +10442,7 @@ fi
 # Restore CFLAGS from before the gcc_AC_NEED_DECLARATIONS tests.
 CFLAGS="$saved_CFLAGS"
 
+# Check if .init_array can be used with .ctors.
 # Check whether --enable-initfini-array was given.
 if test "${enable_initfini_array+set}" = set; then :
   enableval=$enable_initfini_array;
@@ -10452,16 +10453,104 @@ $as_echo_n "checking for .preinit_array/.init_array/.fini_array support... " >&6
 if test "${gcc_cv_initfini_array+set}" = set; then :
   $as_echo_n "(cached) " >&6
 else
+    if test "x${build}" = "x${target}" ; then
     if test "$cross_compiling" = yes; then :
   gcc_cv_initfini_array=no
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
-static int x = -1;
-int main (void) { return x; }
-int foo (void) { x = 0; }
-int (*fp) (void) __attribute__ ((section (".init_array"))) = foo;
+extern void abort ();
+static int count;
+
+static void
+init1005 ()
+{
+  if (count != 0)
+    abort ();
+  count = 1005;
+}
+void (*const init_array1005) ()
+  __attribute__ ((section (".init_array.01005"), aligned (sizeof (void *))))
+  = { init1005 };
+static void
+fini1005 ()
+{
+  if (count != 1005)
+    abort ();
+}
+void (*const fini_array1005) ()
+  __attribute__ ((section (".fini_array.01005"), aligned (sizeof (void *))))
+  = { fini1005 };
+
+static void
+ctor1007 ()
+{
+  if (count != 1005)
+    abort ();
+  count = 1007;
+}
+void (*const ctors1007) ()
+  __attribute__ ((section (".ctors.64528"), aligned (sizeof (void *))))
+  = { ctor1007 };
+static void
+dtor1007 ()
+{
+  if (count != 1007)
+    abort ();
+  count = 1005;
+}
+void (*const dtors1007) ()
+  __attribute__ ((section (".dtors.64528"), aligned (sizeof (void *))))
+  = { dtor1007 };
+
+static void
+init65530 ()
+{
+  if (count != 1007)
+    abort ();
+  count = 65530;
+}
+void (*const init_array65530) ()
+  __attribute__ ((section (".init_array.65530"), aligned (sizeof (void *))))
+  = { init65530 };
+static void
+fini65530 ()
+{
+  if (count != 65530)
+    abort ();
+  count = 1007;
+}
+void (*const fini_array65530) ()
+  __attribute__ ((section (".fini_array.65530"), aligned (sizeof (void *))))
+  = { fini65530 };
+
+static void
+ctor65535 ()
+{
+  if (count != 65530)
+    abort ();
+  count = 65535;
+}
+void (*const ctors65535) ()
+  __attribute__ ((section (".ctors"), aligned (sizeof (void *))))
+  = { ctor65535 };
+static void
+dtor65535 ()
+{
+  if (count != 65535)
+    abort ();
+  count = 65530;
+}
+void (*const dtors65535) ()
+  __attribute__ ((section (".dtors"), aligned (sizeof (void *))))
+  = { dtor65535 };
+
+int
+main ()
+{
+  return 0;
+}
 _ACEOF
 if ac_fn_c_try_run "$LINENO"; then :
   gcc_cv_initfini_array=yes
@@ -10472,6 +10561,9 @@ rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext \
   conftest.$ac_objext conftest.beam conftest.$ac_ext
 fi
 
+   else
+     gcc_cv_initfini_array=no
+   fi
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $gcc_cv_initfini_array" >&5
 $as_echo "$gcc_cv_initfini_array" >&6; }
@@ -17513,7 +17605,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 17516 "configure"
+#line 17608 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -17619,7 +17711,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 17622 "configure"
+#line 17714 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
diff --git a/gcc/configure.ac b/gcc/configure.ac
index 166500e..0937aa3 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -1125,7 +1125,116 @@ fi
 # Restore CFLAGS from before the gcc_AC_NEED_DECLARATIONS tests.
 CFLAGS="$saved_CFLAGS"
 
-gcc_AC_INITFINI_ARRAY
+# Check if .init_array can be used with .ctors.
+AC_ARG_ENABLE(initfini-array,
+	[  --enable-initfini-array	use .init_array/.fini_array sections],
+	[], [
+AC_CACHE_CHECK(for .preinit_array/.init_array/.fini_array support,
+		 gcc_cv_initfini_array, [dnl
+  if test "x${build}" = "x${target}" ; then
+    AC_RUN_IFELSE([AC_LANG_SOURCE([
+extern void abort ();
+static int count;
+
+static void
+init1005 ()
+{
+  if (count != 0)
+    abort ();
+  count = 1005;
+}
+void (*const init_array1005[]) ()
+  __attribute__ ((section (".init_array.01005"), aligned (sizeof (void *))))
+  = { init1005 };
+static void
+fini1005 ()
+{
+  if (count != 1005)
+    abort ();
+}
+void (*const fini_array1005[]) ()
+  __attribute__ ((section (".fini_array.01005"), aligned (sizeof (void *))))
+  = { fini1005 };
+
+static void
+ctor1007 ()
+{
+  if (count != 1005)
+    abort ();
+  count = 1007;
+}
+void (*const ctors1007[]) ()
+  __attribute__ ((section (".ctors.64528"), aligned (sizeof (void *))))
+  = { ctor1007 };
+static void
+dtor1007 ()
+{
+  if (count != 1007)
+    abort ();
+  count = 1005;
+}
+void (*const dtors1007[]) ()
+  __attribute__ ((section (".dtors.64528"), aligned (sizeof (void *))))
+  = { dtor1007 };
+
+static void
+init65530 ()
+{
+  if (count != 1007)
+    abort ();
+  count = 65530;
+}
+void (*const init_array65530[]) ()
+  __attribute__ ((section (".init_array.65530"), aligned (sizeof (void *))))
+  = { init65530 };
+static void
+fini65530 ()
+{
+  if (count != 65530)
+    abort ();
+  count = 1007;
+}
+void (*const fini_array65530[]) ()
+  __attribute__ ((section (".fini_array.65530"), aligned (sizeof (void *))))
+  = { fini65530 };
+
+static void
+ctor65535 ()
+{
+  if (count != 65530)
+    abort ();
+  count = 65535;
+}
+void (*const ctors65535[]) ()
+  __attribute__ ((section (".ctors"), aligned (sizeof (void *))))
+  = { ctor65535 };
+static void
+dtor65535 ()
+{
+  if (count != 65535)
+    abort ();
+  count = 65530;
+}
+void (*const dtors65535[]) ()
+  __attribute__ ((section (".dtors"), aligned (sizeof (void *))))
+  = { dtor65535 };
+
+int
+main ()
+{
+  return 0;
+}])],
+	     [gcc_cv_initfini_array=yes], [gcc_cv_initfini_array=no],
+	     [gcc_cv_initfini_array=no])
+   else
+     gcc_cv_initfini_array=no
+   fi])
+  enable_initfini_array=$gcc_cv_initfini_array
+])
+if test $enable_initfini_array = yes; then
+  AC_DEFINE(HAVE_INITFINI_ARRAY, 1,
+    [Define .init_array/.fini_array sections are available and working.])
+fi
 
 # mkdir takes a single argument on some systems. 
 gcc_AC_FUNC_MKDIR_TAKES_ONE_ARG
diff --git a/gcc/crtstuff.c b/gcc/crtstuff.c
index 6fc571b..2573179 100644
--- a/gcc/crtstuff.c
+++ b/gcc/crtstuff.c
@@ -180,6 +180,9 @@ typedef void (*func_ptr) (void);
    refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
    symbol in crtbegin.o, where they are defined.  */
 
+/* No need for .ctors/.dtors section if linker can place them in
+   .init_array/.fini_array section.  */
+#ifndef NO_CTORS_DTORS_SECTIONS
 /* The -1 is a flag to __do_global_[cd]tors indicating that this table
    does not start with a count of elements.  */
 #ifdef CTOR_LIST_BEGIN
@@ -210,6 +213,7 @@ STATIC func_ptr __DTOR_LIST__[1]
   __attribute__((section(".dtors"), aligned(sizeof(func_ptr))))
   = { (func_ptr) (-1) };
 #endif /* __DTOR_LIST__ alternatives */
+#endif /* NO_CTORS_DTORS_SECTIONS */
 
 #ifdef USE_EH_FRAME_REGISTRY
 /* Stick a label at the beginning of the frame unwind info so we can register
@@ -480,6 +484,9 @@ __do_global_ctors_1(void)
 
 #elif defined(CRT_END) /* ! CRT_BEGIN */
 
+/* No need for .ctors/.dtors section if linker can place them in
+   .init_array/.fini_array section.  */
+#ifndef NO_CTORS_DTORS_SECTIONS
 /* Put a word containing zero at the end of each of our two lists of function
    addresses.  Note that the words defined here go into the .ctors and .dtors
    sections of the crtend.o file, and since that file is always linked in
@@ -525,6 +532,7 @@ STATIC func_ptr __DTOR_END__[1]
   __attribute__((used, section(".dtors"), aligned(sizeof(func_ptr))))
   = { (func_ptr) 0 };
 #endif
+#endif /* NO_CTORS_DTORS_SECTIONS */
 
 #ifdef EH_FRAME_SECTION_NAME
 /* Terminate the frame unwind info section with a 4byte 0 as a sentinel;