user: What would the C source look like for the assembly code provided here:

```asm
<_fillin_sync>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x40,%rsp
  mov    %rdi,-0x38(%rbp)
  mov    %esi,-0x3c(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x8(%rbp)
  xor    %eax,%eax
  mov    -0x3c(%rbp),%eax
  shl    $0x3,%eax
  add    $0xc,%eax
  mov    %eax,-0x2c(%rbp)
  movq   $0x0,-0x20(%rbp)
  movq   $0x0,-0x18(%rbp)
  lea    -0x20(%rbp),%rax
  mov    $0x0,%esi
  mov    %rax,%rdi
  call   <gettimeofday@plt>
  mov    -0x20(%rbp),%eax
  imul   $0x3e8,%eax,%edx
  mov    -0x1c(%rbp),%eax
  add    %edx,%eax
  cltq
  mov    %rax,-0x28(%rbp)
  mov    -0x38(%rbp),%rax
  movb   $0xff,(%rax)
  mov    -0x38(%rbp),%rax
  add    $0x1,%rax
  movb   $0xff,(%rax)
  mov    -0x38(%rbp),%rax
  add    $0x2,%rax
  movb   $0x43,(%rax)
  mov    -0x38(%rbp),%rax
  add    $0x3,%rax
  movb   $0x4b,(%rax)
  mov    -0x38(%rbp),%rax
  add    $0x4,%rax
  movb   $0x5d,(%rax)
  mov    -0x38(%rbp),%rax
  add    $0x5,%rax
  movb   $0x72,(%rax)
  mov    -0x38(%rbp),%rax
  add    $0x6,%rax
  movb   $0xfb,(%rax)
  mov    -0x38(%rbp),%rax
  add    $0x7,%rax
  movb   $0x43,(%rax)
  mov    -0x38(%rbp),%rax
  add    $0x8,%rax
  mov    -0x3c(%rbp),%edx
  mov    %dl,(%rax)
  mov    -0x38(%rbp),%rax
  add    $0x9,%rax
  movb   $0x0,(%rax)
  mov    -0x38(%rbp),%rax
  add    $0xa,%rax
  movb   $0x0,(%rax)
  mov    -0x38(%rbp),%rax
  add    $0xb,%rax
  movb   $0x0,(%rax)
  mov    -0x28(%rbp),%rax
  shr    $0x38,%rax
  mov    %rax,%rcx
  mov    -0x2c(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x38(%rbp),%rax
  add    %rdx,%rax
  mov    %ecx,%edx
  mov    %dl,(%rax)
  mov    -0x28(%rbp),%rax
  shr    $0x30,%rax
  mov    %rax,%rdx
  mov    -0x2c(%rbp),%eax
  cltq
  lea    0x1(%rax),%rcx
  mov    -0x38(%rbp),%rax
  add    %rcx,%rax
  mov    %dl,(%rax)
  mov    -0x28(%rbp),%rax
  shr    $0x28,%rax
  mov    %rax,%rdx
  mov    -0x2c(%rbp),%eax
  cltq
  lea    0x2(%rax),%rcx
  mov    -0x38(%rbp),%rax
  add    %rcx,%rax
  mov    %dl,(%rax)
  mov    -0x28(%rbp),%rax
  shr    $0x20,%rax
  mov    %rax,%rdx
  mov    -0x2c(%rbp),%eax
  cltq
  lea    0x3(%rax),%rcx
  mov    -0x38(%rbp),%rax
  add    %rcx,%rax
  mov    %dl,(%rax)
  mov    -0x28(%rbp),%rax
  shr    $0x18,%rax
  mov    %rax,%rdx
  mov    -0x2c(%rbp),%eax
  cltq
  lea    0x4(%rax),%rcx
  mov    -0x38(%rbp),%rax
  add    %rcx,%rax
  mov    %dl,(%rax)
  mov    -0x28(%rbp),%rax
  shr    $0x10,%rax
  mov    %rax,%rdx
  mov    -0x2c(%rbp),%eax
  cltq
  lea    0x5(%rax),%rcx
  mov    -0x38(%rbp),%rax
  add    %rcx,%rax
  mov    %dl,(%rax)
  mov    -0x28(%rbp),%rax
  shr    $0x8,%rax
  mov    %rax,%rdx
  mov    -0x2c(%rbp),%eax
  cltq
  lea    0x6(%rax),%rcx
  mov    -0x38(%rbp),%rax
  add    %rcx,%rax
  mov    %dl,(%rax)
  mov    -0x2c(%rbp),%eax
  cltq
  lea    0x7(%rax),%rdx
  mov    -0x38(%rbp),%rax
  add    %rdx,%rax
  mov    -0x28(%rbp),%rdx
  mov    %dl,(%rax)
  mov    $0x0,%eax
  mov    -0x8(%rbp),%rdx
  sub    %fs:0x28,%rdx
  je     L2
  call   <__stack_chk_fail@plt>
L2:
  leave
  ret
```

assistant: ```c
int _fillin_sync(unsigned char *buf, int count) {
  int offset = 12 + (8 * count);
  struct timeval tv = {0, 0};
  unsigned long long ts;
  gettimeofday(&tv, NULL);
  ts = tv.tv_sec * 1000 + tv.tv_usec;
  buf[0] = 0xff;
  buf[1] = 0xff;
  buf[2] = 'C';
  buf[3] = 'K';
  buf[4] = 0xff & (0x5d72fb43 >> 24);
  buf[5] = 0xff & (0x5d72fb43 >> 16);
  buf[6] = 0xff & (0x5d72fb43 >> 8);
  buf[7] = 0xff & 0x5d72fb43;
  buf[8] = count;
  buf[9] = 0;
  buf[10] = 0;
  buf[11] = 0;
  buf[offset + 0] = (ts >> 56) & 0xff;
  buf[offset + 1] = (ts >> 48) & 0xff;
  buf[offset + 2] = (ts >> 40) & 0xff;
  buf[offset + 3] = (ts >> 32) & 0xff;
  buf[offset + 4] = (ts >> 24) & 0xff;
  buf[offset + 5] = (ts >> 16) & 0xff;
  buf[offset + 6] = (ts >> 8) & 0xff;
  buf[offset + 7] = ts & 0xff;
  return 0;
}
```