Introduce <elf-initfini.h> and ELF_INITFINI for all architectures

This supersedes the init_array sysdeps directory.  It allows us to
check for ELF_INITFINI in both C and assembler code, and skip DT_INIT
and DT_FINI processing completely on newer architectures.

A new header file is needed because <dl-machine.h> is incompatible
with assembler code.  <sysdep.h> is compatible with assembler code,
but it cannot be included in all assembler files because on some
architectures, it redefines register names, and some assembler files
conflict with that.

<elf-initfini.h> is replicated for legacy architectures which need
DT_INIT/DT_FINI support.  New architectures follow the generic default
and disable it.

3 files changed, 76 insertions, 0 deletions

diff --git a/sysdeps/generic/crti.S b/sysdeps/generic/crti.S
new file mode 100644
index 0000000000..82d6dc0d91
--- /dev/null
+++ b/sysdeps/generic/crti.S
@@ -0,0 +1,33 @@
+/* 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.  */
+
+#include <elf-initfini.h>
+
+#if ELF_INITFINI
+# error Cannot use default crti.S because it lacks _init code
+#endif
+
+#ifdef PREINIT_FUNCTION
+
+# if PREINIT_FUNCTION_WEAK
+#  error PREINIT_FUNCTION_WEAK is unsupported
+# endif
+
+/* This arranges for PREINIT_FUNCTION to be called upon loading a library that
+   contains crti.o.  */
+
+	.section .init_array,"a",%init_array
+	.dc.a PREINIT_FUNCTION
+
+#endif
diff --git a/sysdeps/generic/crtn.S b/sysdeps/generic/crtn.S
new file mode 100644
index 0000000000..d92b07dd0b
--- /dev/null
+++ b/sysdeps/generic/crtn.S
@@ -0,0 +1,19 @@
+/* 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.  */
+
+#include <elf-initfini.h>
+
+#if ELF_INITFINI
+# error Cannot use genetric crtn.S because it lacks _fini code
+#endif
diff --git a/sysdeps/generic/elf-initfini.h b/sysdeps/generic/elf-initfini.h
new file mode 100644
index 0000000000..75e920d283
--- /dev/null
+++ b/sysdeps/generic/elf-initfini.h
@@ -0,0 +1,24 @@
+/* Determine DT_INIT/DT_FINI support in the dynamic loader.
+   Copyright (C) 2020 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.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+/* Legacy platforms define this to 1.  If 0, the dynamic linker
+   ignores the DT_INIT and DT_FINI tags, and static binaries will not
+   call the _init or _fini functions.  If 1, the old constructor
+   mechanisms are used in addition to the initarray/finiarray
+   support.  */
+#define ELF_INITFINI 0