Refactor Linux ARCH_FORK implementation

This patch refactors the ARCH_FORK macro and the required architecture
specific header to simplify the required architecture definitions
to provide the fork syscall semantic and proper document current
Linux clone ABI variant.

Instead of require the reimplementation of arch-fork.h header, this
patch changes the ARCH_FORK to an inline function with clone ABI
defined by kernel-features.h define.  The generic kernel ABI meant
for newer ports is used as default and redefine if the architecture
requires.

Checked on x86_64-linux-gnu and i686-linux-gnu.  Also with a build
for all the afected ABIs.

	* sysdeps/nptl/fork.c (ARCH_FORK): Replace by auch_fork.
	* sysdeps/unix/sysv/linux/alpha/arch-fork.h: Remove file.
	* sysdeps/unix/sysv/linux/riscv/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/aarch64/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/arm/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/hppa/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/i386/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/ia64/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/m68k/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/microblaze/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/mips/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/nios2/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/s390/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/sh/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/sparc/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/tile/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/arch-fork.h: Likewise.
	* sysdeps/unix/sysv/linux/arch-fork.h (arch_fork): New function.
	* sysdeps/unix/sysv/linux/aarch64/kernel-features.h: New file.
	* sysdeps/unix/sysv/linux/riscv/kernel-features.h: Likewise.
	* sysdeps/unix/sysv/linux/arm/kernel-features.h
	(__ASSUME_CLONE_BACKWARDS): Define.
	* sysdeps/unix/sysv/linux/createthread.c (ARCH_CLONE): Define to
	__clone2 if __NR_clone2 is defined.
	* sysdeps/unix/sysv/linux/hppa/kernel-features.h
	(__ASSUME_CLONE_BACKWARDS): Likewise.
	* sysdeps/unix/sysv/linux/i386/kernel-features.h
	(__ASSUME_CLONE_BACKWARDS): Likewise.
	* sysdeps/unix/sysv/linux/ia64/kernel-features.h
	(__ASSUME_CLONE2): Likewise.
	* sysdeps/unix/sysv/linux/microblaze/kernel-features.h
	(__ASSUME_CLONE_BACKWARDS3): Likewise.
	* sysdeps/unix/sysv/linux/kernel-features.h: Document possible clone
	variants and the define architecture can use.
	(__ASSUME_CLONE_DEFAULT): Define as default.
	* sysdeps/unix/sysv/linux/mips/kernel-features.h
	(__ASSUME_CLONE_BACKWARDS): Likewise.
	* sysdeps/unix/sysv/linux/powerpc/kernel-features.h
	(__ASSUME_CLONE_BACKWARDS): Likewise.
	* sysdeps/unix/sysv/linux/s390/kernel-features.h
	(__ASSUME_CLONE_BACKWARDS2): Likewise.

2 files changed, 3 insertions, 27 deletions

diff --git a/sysdeps/unix/sysv/linux/i386/arch-fork.h b/sysdeps/unix/sysv/linux/i386/arch-fork.h
deleted file mode 100644
index 0c43e2fc5c..0000000000
--- a/sysdeps/unix/sysv/linux/i386/arch-fork.h
+++ /dev/null
@@ -1,27 +0,0 @@
-/* Internal definitions for thread-friendly fork implementation.  Linux/i386.
-   Copyright (C) 2002-2018 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
-
-   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
-   <http://www.gnu.org/licenses/>.  */
-
-#include <sched.h>
-#include <sysdep.h>
-#include <tls.h>
-
-#define ARCH_FORK() \
-  INLINE_SYSCALL (clone, 5,						      \
-		  CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID | SIGCHLD, 0,     \
-		  NULL, NULL, &THREAD_SELF->tid)
diff --git a/sysdeps/unix/sysv/linux/i386/kernel-features.h b/sysdeps/unix/sysv/linux/i386/kernel-features.h
index 87087125e5..f3cfd48c44 100644
--- a/sysdeps/unix/sysv/linux/i386/kernel-features.h
+++ b/sysdeps/unix/sysv/linux/i386/kernel-features.h
@@ -48,3 +48,6 @@
 
 /* i686 only supports ipc syscall.  */
 #undef __ASSUME_DIRECT_SYSVIPC_SYSCALLS
+
+#undef __ASSUME_CLONE_DEFAULT
+#define __ASSUME_CLONE_BACKWARDS	1