// An extremely minimalist syscalls.c for newlib
// Based on riscv newlib libgloss/riscv/sys_*.c
// Written by Clifford Wolf.

#include <errno.h>
#include <sys/stat.h>
#include <unistd.h>

#define UNIMPL_FUNC(_f) ".globl " #_f "\n.type " #_f ", @function\n" #_f ":\n"

asm(".text\n"
    ".align 2\n" UNIMPL_FUNC(_open) UNIMPL_FUNC(_openat) UNIMPL_FUNC(_lseek)
        UNIMPL_FUNC(_stat) UNIMPL_FUNC(_lstat) UNIMPL_FUNC(_fstatat)
            UNIMPL_FUNC(_isatty) UNIMPL_FUNC(_access) UNIMPL_FUNC(_faccessat)
                UNIMPL_FUNC(_link) UNIMPL_FUNC(_unlink) UNIMPL_FUNC(_execve)
                    UNIMPL_FUNC(_getpid) UNIMPL_FUNC(_fork) UNIMPL_FUNC(_kill)
                        UNIMPL_FUNC(_wait) UNIMPL_FUNC(_times) UNIMPL_FUNC(
                            _gettimeofday) UNIMPL_FUNC(_ftime)
                            UNIMPL_FUNC(_utime) UNIMPL_FUNC(_chown)
                                UNIMPL_FUNC(_chmod) UNIMPL_FUNC(_chdir)
                                    UNIMPL_FUNC(_getcwd) UNIMPL_FUNC(
                                        _sysconf) "j unimplemented_syscall\n");

void unimplemented_syscall() {
  const char *p = "Unimplemented system call called!\n";
  while (*p) *(volatile int *)0x10000000 = *(p++);
  asm volatile("ebreak");
  __builtin_unreachable();
}

ssize_t _read(int file, void *ptr, size_t len) {
  // always EOF
  return 0;
}

ssize_t _write(int file, const void *ptr, size_t len) {
  const void *eptr = ptr + len;
  while (ptr != eptr) *(volatile int *)0x10000000 = *(char *)(ptr++);
  return len;
}

int _close(int file) {
  // close is called before _exit()
  return 0;
}

int _fstat(int file, struct stat *st) {
  // fstat is called during libc startup
  errno = ENOENT;
  return -1;
}

void *_sbrk(ptrdiff_t incr) {
  extern unsigned char _end[];  // Defined by linker
  static unsigned long heap_end;

  if (heap_end == 0) heap_end = (long)_end;

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

void _exit(int exit_status) {
  asm volatile("li a0, 0x20000000");
  asm volatile("li a1, 123456789");
  asm volatile("sw a1,0(a0)");

  asm volatile("ebreak");
  __builtin_unreachable();
}