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[PATCH roland/csu-init_array] Add sysdeps/init_array to produce empty crt[in].o and use .preinit_array for gcrt1.o
- From: Roland McGrath <roland at hack dot frob dot com>
- To: "GNU C. Library" <libc-alpha at sourceware dot org>
- Date: Wed, 27 Feb 2013 15:49:36 -0800 (PST)
- Subject: [PATCH roland/csu-init_array] Add sysdeps/init_array to produce empty crt[in].o and use .preinit_array for gcrt1.o
New configurations with no legacy toolchain or binary-compatibility
issues (e.g. for new machines or operating systems that never had a
working toolchain before) should completely eschew the old .init/.fini
sections in favor of using only .init_array/.fini_array. This avoids
the need to write any new crt[in].S assembly code.
This patch implements that scheme in a new sysdeps/init_array
directory. New configurations can use an Implies file to get that in
the list, taking care to put it before sysdeps/CPU if it's an existing
CPU that already has sysdeps/CPU/crt[in].S files.
The only part I'm vaguely unsure about is using .preinit_array for
gmon-start. This seems like exactly what .preinit_array is good for,
and I've never actually seen another use of it.
Does anyone see any problems with this scheme?
Thanks,
Roland
2013-02-27 Roland McGrath <roland@hack.frob.com>
* csu/gmon-start.c [GMON_START_ARRAY_SECTION]: Don't define
__gmon_start__ as global, but as static with a .preinit_array pointer.
* sysdeps/init_array/gmon-start.c: New file. Use that.
* sysdeps/init_array/crti.S: New file, empty except for comments.
* sysdeps/init_array/crtn.S: Likewise.
--- a/csu/gmon-start.c
+++ b/csu/gmon-start.c
@@ -59,10 +59,17 @@ extern char etext[];
# endif
#endif
+#ifdef GMON_START_ARRAY_SECTION
+static void __gmon_start__ (void);
+static void (*const gmon_start_initializer) (void)
+ __attribute__ ((used, section (GMON_START_ARRAY_SECTION))) = &__gmon_start__;
+static
+#else
/* We cannot use the normal constructor mechanism to call
__gmon_start__ because gcrt1.o appears before crtbegin.o in the link.
Instead crti.o calls it specially. */
extern void __gmon_start__ (void);
+#endif
void
__gmon_start__ (void)
--- /dev/null
+++ b/sysdeps/init_array/crti.S
@@ -0,0 +1,13 @@
+/* Dummy crti file.
+
+ In this configuration, crti.o and crtn.o are both empty because the
+ .init_array/.fini_array sections are used exclusively.
+
+ Older ports cannot use this because even if the linker used to
+ build libc itself has .init_array support, we don't want to produce
+ a crt[in].o that presume a linker that new will be used to link
+ other things later.
+
+ But new configurations without compatibility concerns for
+ toolchains without .init_array support can use this to avoid the
+ superfluous .init and .fini boilerplate code. */
--- /dev/null
+++ b/sysdeps/init_array/crtn.S
@@ -0,0 +1,13 @@
+/* Dummy crtn file.
+
+ In this configuration, crti.o and crtn.o are both empty because the
+ .init_array/.fini_array sections are used exclusively.
+
+ Older ports cannot use this because even if the linker used to
+ build libc itself has .init_array support, we don't want to produce
+ a crt[in].o that presume a linker that new will be used to link
+ other things later.
+
+ But new configurations without compatibility concerns for
+ toolchains without .init_array support can use this to avoid the
+ superfluous .init and .fini boilerplate code. */
--- /dev/null
+++ b/sysdeps/init_array/gmon-start.c
@@ -0,0 +1,41 @@
+/* gmon startup hook using .preinit_array.
+ Copyright (C) 2013 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ In addition to the permissions in the GNU Lesser General Public
+ License, the Free Software Foundation gives you unlimited
+ permission to link the compiled version of this file with other
+ programs, and to distribute those programs without any restriction
+ coming from the use of this file. (The GNU Lesser General Public
+ License restrictions do apply in other respects; for example, they
+ cover modification of the file, and distribution when not linked
+ into another program.)
+
+ Note that people who make modified versions of this file are not
+ obligated to grant this special exception for their modified
+ versions; it is their choice whether to do so. The GNU Lesser
+ General Public License gives permission to release a modified
+ version without this exception; this exception also makes it
+ possible to release a modified version which carries forward this
+ exception.
+
+ The GNU C Library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+/* Instead of defining __gmon_start__ globally in gcrt1.o, we make it
+ static and just put a pointer to it into the .preinit_array section. */
+
+#defined GMON_START_ARRAY_SECTION ".preinit_array"
+
+#include <csu/gmon-start.c>