futex.2: Casting utime to uint32_t

The kernel uses the following cast:

  if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
      cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
    val2 = (u32) (unsigned long) utime;

This ensures that always the least significant four bytes of the
pointer are used, both on ILP32 and LP64 systems.

On a big endian system a simple cast from 64 bit pointer to 32 bit
integer would return the most significant four bytes.

We have to make the reader of the man-page aware of the usage
of the least significant bytes.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/futex.2

@@ -136,11 +136,13 @@ argument is a pointer to a
 .IR timespec
 structure that specifies a timeout for the operation.
 However,  notwithstanding the prototype shown above, for some operations,
-this argument is instead a four-byte integer whose meaning
+the least significant four bytes are used as an integer whose meaning
 is determined by the operation.
 For these operations, the kernel casts the
 .I timeout
-value to
+value first to
+.IR "unsigned long",
+then to
 .IR uint32_t ,
 and in the remainder of this page, this argument is referred to as
 .I val2