/* Copyright (c) 2017  SiFive Inc. All rights reserved.

   This copyrighted material is made available to anyone wishing to use,
   modify, copy, or redistribute it subject to the terms and conditions
   of the BSD License.   This program is distributed in the hope that
   it will be useful, but WITHOUT ANY WARRANTY expressed or implied,
   including the implied warranties of MERCHANTABILITY or FITNESS FOR
   A PARTICULAR PURPOSE.  A copy of this license is available at
   http://www.opensource.org/licenses.

  ========================================================================
   syscalls.c : Newlib operating system interface
  ========================================================================
   This is the maven implementation of the narrow newlib operating
   system interface. It is based on the minimum stubs in the newlib
   documentation, the error stubs in libnosys, and the previous scale
   implementation. Please do not include any additional system calls or
   other functions in this file. Additional header and source files
   should be in the machine subdirectory.

   Here is a list of the functions which make up the operating system
   interface. The file management instructions execute syscall assembly
   instructions so that a proxy kernel (or the simulator) can marshal up
   the request to the host machine. The process management functions are
   mainly just stubs since for now maven only supports a single process.

    - File management functions
       + open   : (v) open file
       + lseek  : (v) set position in file
       + read   : (v) read from file
       + write  : (v) write to file
       + fstat  : (z) status of an open file
       + stat   : (z) status of a file by name
       + close  : (z) close a file
       + link   : (z) rename a file
       + unlink : (z) remote file's directory entry

    - Process management functions
       + execve : (z) transfer control to new proc
       + fork   : (z) create a new process
       + getpid : (v) get process id
       + kill   : (z) send signal to child process
       + wait   : (z) wait for a child process

    - Misc functions
       + isatty : (v) query whether output stream is a terminal
       + times  : (z) timing information for current process
       + sbrk   : (v) increase program data space
       + _exit  : (-) exit program without cleaning up files

   There are two types of system calls. Those which return a value when
   everything is okay (marked with (v) in above list) and those which
   return a zero when everything is okay (marked with (z) in above
   list). On an error (ie. when the error flag is 1) the return value is
   always an errno which should correspond to the numbers in
   newlib/libc/include/sys/errno.h

   See the newlib documentation for more information
   http://sourceware.org/newlib/libc.html#Syscalls
*/

#include <machine/syscall.h>
#include <sys/stat.h>
#include <sys/times.h>
#include <sys/time.h>
#include <sys/timeb.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <utime.h>

#define syscall_errno(n, a, b, c, d) \
        __internal_syscall(n, (long)(a), (long)(b), (long)(c), (long)(d))

long
__syscall_error(long a0)
{
  errno = -a0;
  return -1;
}

/* Open a file.  */
int
_open(const char *name, int flags, int mode)
{
  return syscall_errno (SYS_open, name, flags, mode, 0);
}

/* Open file relative to given directory.  */
int
_openat(int dirfd, const char *name, int flags, int mode)
{
  return syscall_errno (SYS_openat, dirfd, name, flags, mode);
}

/* Set position in a file.  */
off_t
_lseek(int file, off_t ptr, int dir)
{
  return syscall_errno (SYS_lseek, file, ptr, dir, 0);
}

/* Read from a file.  */
ssize_t
_read(int file, void *ptr, size_t len)
{
  return syscall_errno (SYS_read, file, ptr, len, 0);
}

/* Write to a file.  */
ssize_t
_write(int file, const void *ptr, size_t len)
{
  return syscall_errno (SYS_write, file, ptr, len, 0);
}

struct kernel_stat
{
  unsigned long long st_dev;
  unsigned long long st_ino;
  unsigned int st_mode;
  unsigned int st_nlink;
  unsigned int st_uid;
  unsigned int st_gid;
  unsigned long long st_rdev;
  unsigned long long __pad1;
  long long st_size;
  int st_blksize;
  int __pad2;
  long long st_blocks;
  struct timespec st_atim;
  struct timespec st_mtim;
  struct timespec st_ctim;
  int __glibc_reserved[2];
};

/* Convert linux's stat64 sturct to newlib's stat.  */
static void
conv_stat (struct stat *st, struct kernel_stat *kst)
{
  st->st_dev = kst->st_dev;
  st->st_ino = kst->st_ino;
  st->st_mode = kst->st_mode;
  st->st_nlink = kst->st_nlink;
  st->st_uid = kst->st_uid;
  st->st_gid = kst->st_gid;
  st->st_rdev = kst->st_rdev;
  st->st_size = kst->st_size;
  st->st_blocks = kst->st_blocks;
  st->st_blksize = kst->st_blksize;
  st->st_atime = kst->st_atim.tv_sec;
  st->st_mtime = kst->st_mtim.tv_sec;
  st->st_ctime = kst->st_ctim.tv_sec;
}

/* Status of an open file. The sys/stat.h header file required is
   distributed in the include subdirectory for this C library.  */
int
_fstat(int file, struct stat *st)
{
  struct kernel_stat kst;
  int rv = syscall_errno (SYS_fstat, file, &kst, 0, 0);
  conv_stat (st, &kst);
  return rv;
}

/* Status of a file (by name).  */
int
_stat(const char *file, struct stat *st)
{
  struct kernel_stat kst;
  int rv = syscall_errno (SYS_stat, file, &kst, 0, 0);
  conv_stat (st, &kst);
  return rv;
}

/* Status of a link (by name).  */
int
_lstat(const char *file, struct stat *st)
{
  struct kernel_stat kst;
  int rv = syscall_errno (SYS_lstat, file, &kst, 0, 0);
  conv_stat (st, &kst);
  return rv;
}

/* Status of a file (by name) in a given directory.  */
int
_fstatat(int dirfd, const char *file, struct stat *st, int flags)
{
  struct kernel_stat kst;
  int rv = syscall_errno (SYS_fstatat, dirfd, file, &kst, flags);
  conv_stat (st, &kst);
  return rv;
}

/* Permissions of a file (by name).  */
int
_access(const char *file, int mode)
{
  return syscall_errno (SYS_access, file, mode, 0, 0);
}

/* Permissions of a file (by name) in a given directory.  */
int
_faccessat(int dirfd, const char *file, int mode, int flags)
{
  return syscall_errno (SYS_faccessat, dirfd, file, mode, flags);
}

/* Close a file.  */
int
_close(int file)
{
  return syscall_errno (SYS_close, file, 0, 0, 0);
}

/* Establish a new name for an existing file.  */
int
_link(const char *old_name, const char *new_name)
{
  return syscall_errno (SYS_link, old_name, new_name, 0, 0);
}

/* Remove a file's directory entry.  */
int
_unlink(const char *name)
{
  return syscall_errno (SYS_unlink, name, 0, 0, 0);
}

/* Transfer control to a new process. Minimal implementation for a
   system without processes from newlib documentation.  */
int
_execve(const char *name, char *const argv[], char *const env[])
{
  errno = ENOMEM;
  return -1;
}

/* Create a new process. Minimal implementation for a system without
   processes from newlib documentation.  */

int
_fork()
{
  errno = EAGAIN;
  return -1;
}

/* Get process id. This is sometimes used to generate strings unlikely
   to conflict with other processes. Minimal implementation for a
   system without processes just returns 1.  */

int
_getpid()
{
  return 1;
}

/* Send a signal. Minimal implementation for a system without processes
   just causes an error.  */

int
_kill(int pid, int sig)
{
  errno = EINVAL;
  return -1;
}

/* Wait for a child process. Minimal implementation for a system without
   processes just causes an error.  */

int
_wait(int *status)
{
  errno = ECHILD;
  return -1;
}

/* Query whether output stream is a terminal. For consistency with the
   other minimal implementations, which only support output to stdout,
   this minimal implementation is suggested by the newlib docs.  */

int
_isatty(int file)
{
  struct stat s;
  int ret = _fstat (file, &s);
  return ret == -1 ? -1 : !!(s.st_mode & S_IFCHR);
}

/* Get the current time.  Only relatively correct.  */

int
_gettimeofday(struct timeval *tp, void *tz)
{
  return syscall_errno (SYS_gettimeofday, tp, 0, 0, 0);
}

/* Timing information for current process. From
   newlib/libc/include/sys/times.h the tms struct fields are as follows:

   - clock_t tms_utime  : user clock ticks
   - clock_t tms_stime  : system clock ticks
   - clock_t tms_cutime : children's user clock ticks
   - clock_t tms_cstime : children's system clock ticks

   Since maven does not currently support processes we set both of the
   children's times to zero. Eventually we might want to separately
   account for user vs system time, but for now we just return the total
   number of cycles since starting the program.  */
clock_t
_times(struct tms *buf)
{
  // when called for the first time, initialize t0
  static struct timeval t0;
  if(t0.tv_sec == 0)
    _gettimeofday (&t0,0);

  struct timeval t;
  _gettimeofday (&t, 0);

  long long utime = (t.tv_sec - t0.tv_sec) * 1000000 + (t.tv_usec - t0.tv_usec);
  buf->tms_utime = utime * CLOCKS_PER_SEC / 1000000;
  buf->tms_stime = buf->tms_cstime = buf->tms_cutime = 0;

  return -1;
}

/* Get the current time.  Only relatively correct.  */
int
_ftime(struct timeb *tp)
{
  tp->time = tp->millitm = 0;
  return 0;
}

/* Stub.  */
int
_utime(const char *path, const struct utimbuf *times)
{
  return -1;
}

/* Stub.  */
int
_chown(const char *path, uid_t owner, gid_t group)
{
  return -1;
}

/* Stub.  */
int
_chmod(const char *path, mode_t mode)
{
  return -1;
}

/* Stub.  */
int
_chdir(const char *path)
{
  return -1;
}

/* Stub.  */
char *
_getcwd(char *buf, size_t size)
{
  return NULL;
}

/* Get configurable system variables.  */

long
_sysconf(int name)
{
  switch (name)
    {
    case _SC_CLK_TCK:
      return CLOCKS_PER_SEC;
    }

  return -1;
}

/* Increase program data space. As malloc and related functions depend
   on this, it is useful to have a working implementation. The following
   is suggested by the newlib docs and suffices for a standalone
   system.  */
void *
_sbrk(ptrdiff_t incr)
{
  static unsigned long heap_end;

  if (heap_end == 0)
    {
      long brk = syscall_errno (SYS_brk, 0, 0, 0, 0);
      if (brk == -1)
	return (void *)-1;
      heap_end = brk;
    }

  if (syscall_errno (SYS_brk, heap_end + incr, 0, 0, 0) != heap_end + incr)
    return (void *)-1;

  heap_end += incr;
  return (void *)(heap_end - incr);
}

/* Exit a program without cleaning up files.  */

void
_exit(int exit_status)
{
  syscall_errno (SYS_exit, exit_status, 0, 0, 0);
  while (1);
}