mach, hurd: Cast through uintptr_t

When casting between a pointer and an integer of a different size, GCC
emits a warning (which is escalated to a build failure by -Werror).
Indeed, if what you start with is a pointer, which you then cast to a
shorter integer and then back again, you're going to cut off some bits
of the pointer.

But if you start with an integer (such as mach_port_t), then cast it to
a longer pointer (void *), and then back to a shorter integer, you are
fine. To keep GCC happy, cast through an intermediary uintptr_t, which
is always the same size as a pointer.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
Message-Id: <20230212111044.610942-4-bugaevc@gmail.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/hurd/vpprintf.c b/hurd/vpprintf.c
index fe73494684..010f04ca2c 100644
--- a/hurd/vpprintf.c
+++ b/hurd/vpprintf.c
@@ -25,8 +25,9 @@
 static ssize_t
 do_write (void *cookie,	const char *buf, size_t n)
 {
+  io_t io = (io_t) (uintptr_t) cookie;
   vm_size_t amount = n;
-  error_t error = __io_write ((io_t) cookie, buf, n, -1, &amount);
+  error_t error = __io_write (io, buf, n, -1, &amount);
   if (error)
     return __hurd_fail (error);
   return n;
@@ -51,7 +52,8 @@ vpprintf (io_t port, const char *format, va_list arg)
 #endif
 
   _IO_cookie_init (&temp_f.cfile, _IO_NO_READS,
-		   (void *) port, (cookie_io_functions_t) { write: do_write });
+                   (void *) (uintptr_t) port,
+                   (cookie_io_functions_t) { write: do_write });
 
   done = __vfprintf_internal (&temp_f.cfile.__fp.file, format, arg, 0);