Possible bug in getdents64()?

[Alejandro Colomar <colomar.6.4.3@gmail.com>]

The manual page for getdents64() says the prototype should be the following:

        int getdents64(unsigned int fd, struct linux_dirent64 *dirp,
                     unsigned int count);


Note the type of 'count': 'unsigned int'
(usually a 32-bit unsigned integer).
And the Linux kernel seems to use those types (fs/readdir.c:351):

SYSCALL_DEFINE3(getdents64, unsigned int, fd,
		struct linux_dirent64 __user *, dirent,
		unsigned int, count)
{
...
}

But glibc uses 'size_t' (usually a 64-bit unsigned integer)
for the parameter 'count' (sysdeps/unix/linux/getdents64.c:25):


/* The kernel struct linux_dirent64 matches the 'struct dirent64' type.  */
ssize_t
__getdents64 (int fd, void *buf, size_t nbytes)
{
   /* The system call takes an unsigned int argument, and some length
      checks in the kernel use an int type.  */
   if (nbytes > INT_MAX)
     nbytes = INT_MAX;
   return INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
}
libc_hidden_def (__getdents64)
weak_alias (__getdents64, getdents64)



Isn't it undefined behavior to pass a variable of a different (larger) 
type to a variadic function than what it expects?

Is that behavior defined in this implementation?

Wouldn't a cast to 'unsigned int' be needed?


Thanks,

Alex