Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:
 "The biggest RCU changes in this cycle were:

   - Convert RCU's BUG_ON() and similar calls to WARN_ON() and similar.

   - Replace calls of RCU-bh and RCU-sched update-side functions to
     their vanilla RCU counterparts. This series is a step towards
     complete removal of the RCU-bh and RCU-sched update-side functions.

     ( Note that some of these conversions are going upstream via their
       respective maintainers. )

   - Documentation updates, including a number of flavor-consolidation
     updates from Joel Fernandes.

   - Miscellaneous fixes.

   - Automate generation of the initrd filesystem used for rcutorture
     testing.

   - Convert spin_is_locked() assertions to instead use lockdep.

     ( Note that some of these conversions are going upstream via their
       respective maintainers. )

   - SRCU updates, especially including a fix from Dennis Krein for a
     bag-on-head-class bug.

   - RCU torture-test updates"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (112 commits)
  rcutorture: Don't do busted forward-progress testing
  rcutorture: Use 100ms buckets for forward-progress callback histograms
  rcutorture: Recover from OOM during forward-progress tests
  rcutorture: Print forward-progress test age upon failure
  rcutorture: Print time since GP end upon forward-progress failure
  rcutorture: Print histogram of CB invocation at OOM time
  rcutorture: Print GP age upon forward-progress failure
  rcu: Print per-CPU callback counts for forward-progress failures
  rcu: Account for nocb-CPU callback counts in RCU CPU stall warnings
  rcutorture: Dump grace-period diagnostics upon forward-progress OOM
  rcutorture: Prepare for asynchronous access to rcu_fwd_startat
  torture: Remove unnecessary "ret" variables
  rcutorture: Affinity forward-progress test to avoid housekeeping CPUs
  rcutorture: Break up too-long rcu_torture_fwd_prog() function
  rcutorture: Remove cbflood facility
  torture: Bring any extra CPUs online during kernel startup
  rcutorture: Add call_rcu() flooding forward-progress tests
  rcutorture/formal: Replace synchronize_sched() with synchronize_rcu()
  tools/kernel.h: Replace synchronize_sched() with synchronize_rcu()
  net/decnet: Replace rcu_barrier_bh() with rcu_barrier()
  ...

5 files changed, 2355 insertions, 89 deletions

diff --git a/tools/testing/selftests/rcutorture/bin/kvm.sh b/tools/testing/selftests/rcutorture/bin/kvm.sh
index 5a7a62d76a50..19864f1cb27a 100755
--- a/tools/testing/selftests/rcutorture/bin/kvm.sh
+++ b/tools/testing/selftests/rcutorture/bin/kvm.sh
@@ -194,6 +194,14 @@ do
 	shift
 done
 
+if test -z "$TORTURE_INITRD" || tools/testing/selftests/rcutorture/bin/mkinitrd.sh
+then
+	:
+else
+	echo No initrd and unable to create one, aborting test >&2
+	exit 1
+fi
+
 CONFIGFRAG=${KVM}/configs/${TORTURE_SUITE}; export CONFIGFRAG
 
 if test -z "$configs"
diff --git a/tools/testing/selftests/rcutorture/bin/mkinitrd.sh b/tools/testing/selftests/rcutorture/bin/mkinitrd.sh
new file mode 100755
index 000000000000..da298394daa2
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/bin/mkinitrd.sh
@@ -0,0 +1,136 @@
+#!/bin/bash
+#
+# Create an initrd directory if one does not already exist.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, you can access it online at
+# http://www.gnu.org/licenses/gpl-2.0.html.
+#
+# Copyright (C) IBM Corporation, 2013
+#
+# Author: Connor Shu <Connor.Shu@ibm.com>
+
+D=tools/testing/selftests/rcutorture
+
+# Prerequisite checks
+[ -z "$D" ] && echo >&2 "No argument supplied" && exit 1
+if [ ! -d "$D" ]; then
+    echo >&2 "$D does not exist: Malformed kernel source tree?"
+    exit 1
+fi
+if [ -s "$D/initrd/init" ]; then
+    echo "$D/initrd/init already exists, no need to create it"
+    exit 0
+fi
+
+T=${TMPDIR-/tmp}/mkinitrd.sh.$$
+trap 'rm -rf $T' 0 2
+mkdir $T
+
+cat > $T/init << '__EOF___'
+#!/bin/sh
+# Run in userspace a few milliseconds every second.  This helps to
+# exercise the NO_HZ_FULL portions of RCU.
+while :
+do
+	q=
+	for i in \
+		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \
+		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \
+		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \
+		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \
+		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \
+		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
+	do
+		q="$q $i"
+	done
+	sleep 1
+done
+__EOF___
+
+# Try using dracut to create initrd
+if command -v dracut >/dev/null 2>&1
+then
+	echo Creating $D/initrd using dracut.
+	# Filesystem creation
+	dracut --force --no-hostonly --no-hostonly-cmdline --module "base" $T/initramfs.img
+	cd $D
+	mkdir -p initrd
+	cd initrd
+	zcat $T/initramfs.img | cpio -id
+	cp $T/init init
+	chmod +x init
+	echo Done creating $D/initrd using dracut
+	exit 0
+fi
+
+# No dracut, so create a C-language initrd/init program and statically
+# link it.  This results in a very small initrd, but might be a bit less
+# future-proof than dracut.
+echo "Could not find dracut, attempting C initrd"
+cd $D
+mkdir -p initrd
+cd initrd
+cat > init.c << '___EOF___'
+#ifndef NOLIBC
+#include <unistd.h>
+#include <sys/time.h>
+#endif
+
+volatile unsigned long delaycount;
+
+int main(int argc, int argv[])
+{
+	int i;
+	struct timeval tv;
+	struct timeval tvb;
+
+	for (;;) {
+		sleep(1);
+		/* Need some userspace time. */
+		if (gettimeofday(&tvb, NULL))
+			continue;
+		do {
+			for (i = 0; i < 1000 * 100; i++)
+				delaycount = i * i;
+			if (gettimeofday(&tv, NULL))
+				break;
+			tv.tv_sec -= tvb.tv_sec;
+			if (tv.tv_sec > 1)
+				break;
+			tv.tv_usec += tv.tv_sec * 1000 * 1000;
+			tv.tv_usec -= tvb.tv_usec;
+		} while (tv.tv_usec < 1000);
+	}
+	return 0;
+}
+___EOF___
+
+# build using nolibc on supported archs (smaller executable) and fall
+# back to regular glibc on other ones.
+if echo -e "#if __x86_64__||__i386__||__i486__||__i586__||__i686__" \
+           "||__ARM_EABI__||__aarch64__\nyes\n#endif" \
+   | ${CROSS_COMPILE}gcc -E -nostdlib -xc - \
+   | grep -q '^yes'; then
+	# architecture supported by nolibc
+        ${CROSS_COMPILE}gcc -fno-asynchronous-unwind-tables -fno-ident \
+		-nostdlib -include ../bin/nolibc.h -lgcc -s -static -Os \
+		-o init init.c
+else
+	${CROSS_COMPILE}gcc -s -static -Os -o init init.c
+fi
+
+rm init.c
+echo "Done creating a statically linked C-language initrd"
+
+exit 0
diff --git a/tools/testing/selftests/rcutorture/bin/nolibc.h b/tools/testing/selftests/rcutorture/bin/nolibc.h
new file mode 100644
index 000000000000..f98f5b92d3eb
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/bin/nolibc.h
@@ -0,0 +1,2197 @@
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+/* nolibc.h
+ * Copyright (C) 2017-2018 Willy Tarreau <w@1wt.eu>
+ */
+
+/* some archs (at least aarch64) don't expose the regular syscalls anymore by
+ * default, either because they have an "_at" replacement, or because there are
+ * more modern alternatives. For now we'd rather still use them.
+ */
+#define __ARCH_WANT_SYSCALL_NO_AT
+#define __ARCH_WANT_SYSCALL_NO_FLAGS
+#define __ARCH_WANT_SYSCALL_DEPRECATED
+
+#include <asm/unistd.h>
+#include <asm/ioctls.h>
+#include <asm/errno.h>
+#include <linux/fs.h>
+#include <linux/loop.h>
+
+#define NOLIBC
+
+/* Build a static executable this way :
+ *      $ gcc -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \
+ *            -static -include nolibc.h -lgcc -o hello hello.c
+ *
+ * Useful calling convention table found here :
+ *      http://man7.org/linux/man-pages/man2/syscall.2.html
+ *
+ * This doc is even better :
+ *      https://w3challs.com/syscalls/
+ */
+
+
+/* this way it will be removed if unused */
+static int errno;
+
+#ifndef NOLIBC_IGNORE_ERRNO
+#define SET_ERRNO(v) do { errno = (v); } while (0)
+#else
+#define SET_ERRNO(v) do { } while (0)
+#endif
+
+/* errno codes all ensure that they will not conflict with a valid pointer
+ * because they all correspond to the highest addressable memry page.
+ */
+#define MAX_ERRNO 4095
+
+/* Declare a few quite common macros and types that usually are in stdlib.h,
+ * stdint.h, ctype.h, unistd.h and a few other common locations.
+ */
+
+#define NULL ((void *)0)
+
+/* stdint types */
+typedef unsigned char       uint8_t;
+typedef   signed char        int8_t;
+typedef unsigned short     uint16_t;
+typedef   signed short      int16_t;
+typedef unsigned int       uint32_t;
+typedef   signed int        int32_t;
+typedef unsigned long long uint64_t;
+typedef   signed long long  int64_t;
+typedef unsigned long        size_t;
+typedef   signed long       ssize_t;
+typedef unsigned long     uintptr_t;
+typedef   signed long      intptr_t;
+typedef   signed long     ptrdiff_t;
+
+/* for stat() */
+typedef unsigned int          dev_t;
+typedef unsigned long         ino_t;
+typedef unsigned int         mode_t;
+typedef   signed int          pid_t;
+typedef unsigned int          uid_t;
+typedef unsigned int          gid_t;
+typedef unsigned long       nlink_t;
+typedef   signed long         off_t;
+typedef   signed long     blksize_t;
+typedef   signed long      blkcnt_t;
+typedef   signed long        time_t;
+
+/* for poll() */
+struct pollfd {
+    int fd;
+    short int events;
+    short int revents;
+};
+
+/* for select() */
+struct timeval {
+	long    tv_sec;
+	long    tv_usec;
+};
+
+/* for pselect() */
+struct timespec {
+	long    tv_sec;
+	long    tv_nsec;
+};
+
+/* for gettimeofday() */
+struct timezone {
+	int tz_minuteswest;
+	int tz_dsttime;
+};
+
+/* for getdents64() */
+struct linux_dirent64 {
+	uint64_t       d_ino;
+	int64_t        d_off;
+	unsigned short d_reclen;
+	unsigned char  d_type;
+	char           d_name[];
+};
+
+/* commonly an fd_set represents 256 FDs */
+#define FD_SETSIZE 256
+typedef struct { uint32_t fd32[FD_SETSIZE/32]; } fd_set;
+
+/* needed by wait4() */
+struct rusage {
+	struct timeval ru_utime;
+	struct timeval ru_stime;
+	long   ru_maxrss;
+	long   ru_ixrss;
+	long   ru_idrss;
+	long   ru_isrss;
+	long   ru_minflt;
+	long   ru_majflt;
+	long   ru_nswap;
+	long   ru_inblock;
+	long   ru_oublock;
+	long   ru_msgsnd;
+	long   ru_msgrcv;
+	long   ru_nsignals;
+	long   ru_nvcsw;
+	long   ru_nivcsw;
+};
+
+/* stat flags (WARNING, octal here) */
+#define S_IFDIR       0040000
+#define S_IFCHR       0020000
+#define S_IFBLK       0060000
+#define S_IFREG       0100000
+#define S_IFIFO       0010000
+#define S_IFLNK       0120000
+#define S_IFSOCK      0140000
+#define S_IFMT        0170000
+
+#define S_ISDIR(mode)  (((mode) & S_IFDIR) == S_IFDIR)
+#define S_ISCHR(mode)  (((mode) & S_IFCHR) == S_IFCHR)
+#define S_ISBLK(mode)  (((mode) & S_IFBLK) == S_IFBLK)
+#define S_ISREG(mode)  (((mode) & S_IFREG) == S_IFREG)
+#define S_ISFIFO(mode) (((mode) & S_IFIFO) == S_IFIFO)
+#define S_ISLNK(mode)  (((mode) & S_IFLNK) == S_IFLNK)
+#define S_ISSOCK(mode) (((mode) & S_IFSOCK) == S_IFSOCK)
+
+#define DT_UNKNOWN 0
+#define DT_FIFO    1
+#define DT_CHR     2
+#define DT_DIR     4
+#define DT_BLK     6
+#define DT_REG     8
+#define DT_LNK    10
+#define DT_SOCK   12
+
+/* all the *at functions */
+#ifndef AT_FDWCD
+#define AT_FDCWD             -100
+#endif
+
+/* lseek */
+#define SEEK_SET        0
+#define SEEK_CUR        1
+#define SEEK_END        2
+
+/* reboot */
+#define LINUX_REBOOT_MAGIC1         0xfee1dead
+#define LINUX_REBOOT_MAGIC2         0x28121969
+#define LINUX_REBOOT_CMD_HALT       0xcdef0123
+#define LINUX_REBOOT_CMD_POWER_OFF  0x4321fedc
+#define LINUX_REBOOT_CMD_RESTART    0x01234567
+#define LINUX_REBOOT_CMD_SW_SUSPEND 0xd000fce2
+
+
+/* The format of the struct as returned by the libc to the application, which
+ * significantly differs from the format returned by the stat() syscall flavours.
+ */
+struct stat {
+	dev_t     st_dev;     /* ID of device containing file */
+	ino_t     st_ino;     /* inode number */
+	mode_t    st_mode;    /* protection */
+	nlink_t   st_nlink;   /* number of hard links */
+	uid_t     st_uid;     /* user ID of owner */
+	gid_t     st_gid;     /* group ID of owner */
+	dev_t     st_rdev;    /* device ID (if special file) */
+	off_t     st_size;    /* total size, in bytes */
+	blksize_t st_blksize; /* blocksize for file system I/O */
+	blkcnt_t  st_blocks;  /* number of 512B blocks allocated */
+	time_t    st_atime;   /* time of last access */
+	time_t    st_mtime;   /* time of last modification */
+	time_t    st_ctime;   /* time of last status change */
+};
+
+#define WEXITSTATUS(status)   (((status) & 0xff00) >> 8)
+#define WIFEXITED(status)     (((status) & 0x7f) == 0)
+
+
+/* Below comes the architecture-specific code. For each architecture, we have
+ * the syscall declarations and the _start code definition. This is the only
+ * global part. On all architectures the kernel puts everything in the stack
+ * before jumping to _start just above us, without any return address (_start
+ * is not a function but an entry pint). So at the stack pointer we find argc.
+ * Then argv[] begins, and ends at the first NULL. Then we have envp which
+ * starts and ends with a NULL as well. So envp=argv+argc+1.
+ */
+
+#if defined(__x86_64__)
+/* Syscalls for x86_64 :
+ *   - registers are 64-bit
+ *   - syscall number is passed in rax
+ *   - arguments are in rdi, rsi, rdx, r10, r8, r9 respectively
+ *   - the system call is performed by calling the syscall instruction
+ *   - syscall return comes in rax
+ *   - rcx and r8..r11 may be clobbered, others are preserved.
+ *   - the arguments are cast to long and assigned into the target registers
+ *     which are then simply passed as registers to the asm code, so that we
+ *     don't have to experience issues with register constraints.
+ *   - the syscall number is always specified last in order to allow to force
+ *     some registers before (gcc refuses a %-register at the last position).
+ */
+
+#define my_syscall0(num)                                                      \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num  asm("rax") = (num);                               \
+									      \
+	asm volatile (                                                        \
+		"syscall\n"                                                   \
+		: "=a" (_ret)                                                 \
+		: "0"(_num)                                                   \
+		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"                                \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall1(num, arg1)                                                \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num  asm("rax") = (num);                               \
+	register long _arg1 asm("rdi") = (long)(arg1);                        \
+									      \
+	asm volatile (                                                        \
+		"syscall\n"                                                   \
+		: "=a" (_ret)                                                 \
+		: "r"(_arg1),                                                 \
+		  "0"(_num)                                                   \
+		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"                                \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall2(num, arg1, arg2)                                          \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num  asm("rax") = (num);                               \
+	register long _arg1 asm("rdi") = (long)(arg1);                        \
+	register long _arg2 asm("rsi") = (long)(arg2);                        \
+									      \
+	asm volatile (                                                        \
+		"syscall\n"                                                   \
+		: "=a" (_ret)                                                 \
+		: "r"(_arg1), "r"(_arg2),                                     \
+		  "0"(_num)                                                   \
+		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"                                \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall3(num, arg1, arg2, arg3)                                    \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num  asm("rax") = (num);                               \
+	register long _arg1 asm("rdi") = (long)(arg1);                        \
+	register long _arg2 asm("rsi") = (long)(arg2);                        \
+	register long _arg3 asm("rdx") = (long)(arg3);                        \
+									      \
+	asm volatile (                                                        \
+		"syscall\n"                                                   \
+		: "=a" (_ret)                                                 \
+		: "r"(_arg1), "r"(_arg2), "r"(_arg3),                         \
+		  "0"(_num)                                                   \
+		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"                                \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall4(num, arg1, arg2, arg3, arg4)                              \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num  asm("rax") = (num);                               \
+	register long _arg1 asm("rdi") = (long)(arg1);                        \
+	register long _arg2 asm("rsi") = (long)(arg2);                        \
+	register long _arg3 asm("rdx") = (long)(arg3);                        \
+	register long _arg4 asm("r10") = (long)(arg4);                        \
+									      \
+	asm volatile (                                                        \
+		"syscall\n"                                                   \
+		: "=a" (_ret), "=r"(_arg4)                                    \
+		: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4),             \
+		  "0"(_num)                                                   \
+		: "rcx", "r8", "r9", "r11", "memory", "cc"                    \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall5(num, arg1, arg2, arg3, arg4, arg5)                        \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num  asm("rax") = (num);                               \
+	register long _arg1 asm("rdi") = (long)(arg1);                        \
+	register long _arg2 asm("rsi") = (long)(arg2);                        \
+	register long _arg3 asm("rdx") = (long)(arg3);                        \
+	register long _arg4 asm("r10") = (long)(arg4);                        \
+	register long _arg5 asm("r8")  = (long)(arg5);                        \
+									      \
+	asm volatile (                                                        \
+		"syscall\n"                                                   \
+		: "=a" (_ret), "=r"(_arg4), "=r"(_arg5)                       \
+		: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
+		  "0"(_num)                                                   \
+		: "rcx", "r9", "r11", "memory", "cc"                          \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6)                  \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num  asm("rax") = (num);                               \
+	register long _arg1 asm("rdi") = (long)(arg1);                        \
+	register long _arg2 asm("rsi") = (long)(arg2);                        \
+	register long _arg3 asm("rdx") = (long)(arg3);                        \
+	register long _arg4 asm("r10") = (long)(arg4);                        \
+	register long _arg5 asm("r8")  = (long)(arg5);                        \
+	register long _arg6 asm("r9")  = (long)(arg6);                        \
+									      \
+	asm volatile (                                                        \
+		"syscall\n"                                                   \
+		: "=a" (_ret), "=r"(_arg4), "=r"(_arg5)                       \
+		: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
+		  "r"(_arg6), "0"(_num)                                       \
+		: "rcx", "r11", "memory", "cc"                                \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+/* startup code */
+asm(".section .text\n"
+    ".global _start\n"
+    "_start:\n"
+    "pop %rdi\n"                // argc   (first arg, %rdi)
+    "mov %rsp, %rsi\n"          // argv[] (second arg, %rsi)
+    "lea 8(%rsi,%rdi,8),%rdx\n" // then a NULL then envp (third arg, %rdx)
+    "and $-16, %rsp\n"          // x86 ABI : esp must be 16-byte aligned when
+    "sub $8, %rsp\n"            // entering the callee
+    "call main\n"               // main() returns the status code, we'll exit with it.
+    "movzb %al, %rdi\n"         // retrieve exit code from 8 lower bits
+    "mov $60, %rax\n"           // NR_exit == 60
+    "syscall\n"                 // really exit
+    "hlt\n"                     // ensure it does not return
+    "");
+
+/* fcntl / open */
+#define O_RDONLY            0
+#define O_WRONLY            1
+#define O_RDWR              2
+#define O_CREAT          0x40
+#define O_EXCL           0x80
+#define O_NOCTTY        0x100
+#define O_TRUNC         0x200
+#define O_APPEND        0x400
+#define O_NONBLOCK      0x800
+#define O_DIRECTORY   0x10000
+
+/* The struct returned by the stat() syscall, equivalent to stat64(). The
+ * syscall returns 116 bytes and stops in the middle of __unused.
+ */
+struct sys_stat_struct {
+	unsigned long st_dev;
+	unsigned long st_ino;
+	unsigned long st_nlink;
+	unsigned int  st_mode;
+	unsigned int  st_uid;
+
+	unsigned int  st_gid;
+	unsigned int  __pad0;
+	unsigned long st_rdev;
+	long          st_size;
+	long          st_blksize;
+
+	long          st_blocks;
+	unsigned long st_atime;
+	unsigned long st_atime_nsec;
+	unsigned long st_mtime;
+
+	unsigned long st_mtime_nsec;
+	unsigned long st_ctime;
+	unsigned long st_ctime_nsec;
+	long          __unused[3];
+};
+
+#elif defined(__i386__) || defined(__i486__) || defined(__i586__) || defined(__i686__)
+/* Syscalls for i386 :
+ *   - mostly similar to x86_64
+ *   - registers are 32-bit
+ *   - syscall number is passed in eax
+ *   - arguments are in ebx, ecx, edx, esi, edi, ebp respectively
+ *   - all registers are preserved (except eax of course)
+ *   - the system call is performed by calling int $0x80
+ *   - syscall return comes in eax
+ *   - the arguments are cast to long and assigned into the target registers
+ *     which are then simply passed as registers to the asm code, so that we
+ *     don't have to experience issues with register constraints.
+ *   - the syscall number is always specified last in order to allow to force
+ *     some registers before (gcc refuses a %-register at the last position).
+ *
+ * Also, i386 supports the old_select syscall if newselect is not available
+ */
+#define __ARCH_WANT_SYS_OLD_SELECT
+
+#define my_syscall0(num)                                                      \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num asm("eax") = (num);                                \
+									      \
+	asm volatile (                                                        \
+		"int $0x80\n"                                                 \
+		: "=a" (_ret)                                                 \
+		: "0"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall1(num, arg1)                                                \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num asm("eax") = (num);                                \
+	register long _arg1 asm("ebx") = (long)(arg1);                        \
+									      \
+	asm volatile (                                                        \
+		"int $0x80\n"                                                 \
+		: "=a" (_ret)                                                 \
+		: "r"(_arg1),                                                 \
+		  "0"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall2(num, arg1, arg2)                                          \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num asm("eax") = (num);                                \
+	register long _arg1 asm("ebx") = (long)(arg1);                        \
+	register long _arg2 asm("ecx") = (long)(arg2);                        \
+									      \
+	asm volatile (                                                        \
+		"int $0x80\n"                                                 \
+		: "=a" (_ret)                                                 \
+		: "r"(_arg1), "r"(_arg2),                                     \
+		  "0"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall3(num, arg1, arg2, arg3)                                    \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num asm("eax") = (num);                                \
+	register long _arg1 asm("ebx") = (long)(arg1);                        \
+	register long _arg2 asm("ecx") = (long)(arg2);                        \
+	register long _arg3 asm("edx") = (long)(arg3);                        \
+									      \
+	asm volatile (                                                        \
+		"int $0x80\n"                                                 \
+		: "=a" (_ret)                                                 \
+		: "r"(_arg1), "r"(_arg2), "r"(_arg3),                         \
+		  "0"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall4(num, arg1, arg2, arg3, arg4)                              \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num asm("eax") = (num);                                \
+	register long _arg1 asm("ebx") = (long)(arg1);                        \
+	register long _arg2 asm("ecx") = (long)(arg2);                        \
+	register long _arg3 asm("edx") = (long)(arg3);                        \
+	register long _arg4 asm("esi") = (long)(arg4);                        \
+									      \
+	asm volatile (                                                        \
+		"int $0x80\n"                                                 \
+		: "=a" (_ret)                                                 \
+		: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4),             \
+		  "0"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall5(num, arg1, arg2, arg3, arg4, arg5)                        \
+({                                                                            \
+	long _ret;                                                            \
+	register long _num asm("eax") = (num);                                \
+	register long _arg1 asm("ebx") = (long)(arg1);                        \
+	register long _arg2 asm("ecx") = (long)(arg2);                        \
+	register long _arg3 asm("edx") = (long)(arg3);                        \
+	register long _arg4 asm("esi") = (long)(arg4);                        \
+	register long _arg5 asm("edi") = (long)(arg5);                        \
+									      \
+	asm volatile (                                                        \
+		"int $0x80\n"                                                 \
+		: "=a" (_ret)                                                 \
+		: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
+		  "0"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+/* startup code */
+asm(".section .text\n"
+    ".global _start\n"
+    "_start:\n"
+    "pop %eax\n"                // argc   (first arg, %eax)
+    "mov %esp, %ebx\n"          // argv[] (second arg, %ebx)
+    "lea 4(%ebx,%eax,4),%ecx\n" // then a NULL then envp (third arg, %ecx)
+    "and $-16, %esp\n"          // x86 ABI : esp must be 16-byte aligned when
+    "push %ecx\n"               // push all registers on the stack so that we
+    "push %ebx\n"               // support both regparm and plain stack modes
+    "push %eax\n"
+    "call main\n"               // main() returns the status code in %eax
+    "movzbl %al, %ebx\n"        // retrieve exit code from lower 8 bits
+    "movl   $1, %eax\n"         // NR_exit == 1
+    "int    $0x80\n"            // exit now
+    "hlt\n"                     // ensure it does not
+    "");
+
+/* fcntl / open */
+#define O_RDONLY            0
+#define O_WRONLY            1
+#define O_RDWR              2
+#define O_CREAT          0x40
+#define O_EXCL           0x80
+#define O_NOCTTY        0x100
+#define O_TRUNC         0x200
+#define O_APPEND        0x400
+#define O_NONBLOCK      0x800
+#define O_DIRECTORY   0x10000
+
+/* The struct returned by the stat() syscall, 32-bit only, the syscall returns
+ * exactly 56 bytes (stops before the unused array).
+ */
+struct sys_stat_struct {
+	unsigned long  st_dev;
+	unsigned long  st_ino;
+	unsigned short st_mode;
+	unsigned short st_nlink;
+	unsigned short st_uid;
+	unsigned short st_gid;
+
+	unsigned long  st_rdev;
+	unsigned long  st_size;
+	unsigned long  st_blksize;
+	unsigned long  st_blocks;
+
+	unsigned long  st_atime;
+	unsigned long  st_atime_nsec;
+	unsigned long  st_mtime;
+	unsigned long  st_mtime_nsec;
+
+	unsigned long  st_ctime;
+	unsigned long  st_ctime_nsec;
+	unsigned long  __unused[2];
+};
+
+#elif defined(__ARM_EABI__)
+/* Syscalls for ARM in ARM or Thumb modes :
+ *   - registers are 32-bit
+ *   - stack is 8-byte aligned
+ *     ( http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka4127.html)
+ *   - syscall number is passed in r7
+ *   - arguments are in r0, r1, r2, r3, r4, r5
+ *   - the system call is performed by calling svc #0
+ *   - syscall return comes in r0.
+ *   - only lr is clobbered.
+ *   - the arguments are cast to long and assigned into the target registers
+ *     which are then simply passed as registers to the asm code, so that we
+ *     don't have to experience issues with register constraints.
+ *   - the syscall number is always specified last in order to allow to force
+ *     some registers before (gcc refuses a %-register at the last position).
+ *
+ * Also, ARM supports the old_select syscall if newselect is not available
+ */
+#define __ARCH_WANT_SYS_OLD_SELECT
+
+#define my_syscall0(num)                                                      \
+({                                                                            \
+	register long _num asm("r7") = (num);                                 \
+	register long _arg1 asm("r0");                                        \
+									      \
+	asm volatile (                                                        \
+		"svc #0\n"                                                    \
+		: "=r"(_arg1)                                                 \
+		: "r"(_num)                                                   \
+		: "memory", "cc", "lr"                                        \
+	);                                                                    \
+	_arg1;                                                                \
+})
+
+#define my_syscall1(num, arg1)                                                \
+({                                                                            \
+	register long _num asm("r7") = (num);                                 \
+	register long _arg1 asm("r0") = (long)(arg1);                         \
+									      \
+	asm volatile (                                                        \
+		"svc #0\n"                                                    \
+		: "=r"(_arg1)                                                 \
+		: "r"(_arg1),                                                 \
+		  "r"(_num)                                                   \
+		: "memory", "cc", "lr"                                        \
+	);                                                                    \
+	_arg1;                                                                \
+})
+
+#define my_syscall2(num, arg1, arg2)                                          \
+({                                                                            \
+	register long _num asm("r7") = (num);                                 \
+	register long _arg1 asm("r0") = (long)(arg1);                         \
+	register long _arg2 asm("r1") = (long)(arg2);                         \
+									      \
+	asm volatile (                                                        \
+		"svc #0\n"                                                    \
+		: "=r"(_arg1)                                                 \
+		: "r"(_arg1), "r"(_arg2),                                     \
+		  "r"(_num)                                                   \
+		: "memory", "cc", "lr"                                        \
+	);