Update hurd/hurdselect.c to be more portable.

Summary of changes:
- Use BAD_TYPECHECK to perform type checking in a cleaner way.
  BAD_TYPECHECK is moved into sysdeps/mach/rpc.h to avoid duplication.
- Remove assertions for mach_msg_type_t since those won't work for
  x86_64.
- Update message structs to use mach_msg_type_t directly.
- Use designated initializers.
Message-Id: <ZFa+roan3ioo0ONM@jupiter.tail36e24.ts.net>

hurd/hurdselect.c

@@ -22,6 +22,7 @@
 #include <hurd.h>
 #include <hurd/fd.h>
 #include <hurd/io_request.h>
+#include <mach_rpc.h>
 #include <stdlib.h>
 #include <string.h>
 #include <assert.h>
@@ -69,14 +70,6 @@ _hurd_select (int nfds,
   sigset_t oset;
   struct hurd_sigstate *ss = NULL;
 
-  union typeword		/* Use this to avoid unkosher casts.  */
-    {
-      mach_msg_type_t type;
-      uint32_t word;
-    };
-  assert (sizeof (union typeword) == sizeof (mach_msg_type_t));
-  assert (sizeof (uint32_t) == sizeof (mach_msg_type_t));
-
   if (nfds < 0 || (pollfds == NULL && nfds > FD_SETSIZE))
     {
       errno = EINVAL;
@@ -404,15 +397,15 @@ _hurd_select (int nfds,
 	  struct
 	    {
 	      mach_msg_header_t head;
-	      union typeword err_type;
+	      mach_msg_type_t err_type;
 	      error_t err;
 	    } error;
 	  struct
 	    {
 	      mach_msg_header_t head;
-	      union typeword err_type;
+	      mach_msg_type_t err_type;
 	      error_t err;
-	      union typeword result_type;
+	      mach_msg_type_t result_type;
 	      int result;
 	    } success;
 #endif
@@ -443,9 +436,14 @@ _hurd_select (int nfds,
 
 	  /* We got a message.  Decode it.  */
 #ifdef MACH_MSG_TYPE_BIT
-	  const union typeword inttype =
+	  static const mach_msg_type_t inttype = {
-	  { type:
+	    .msgt_name = MACH_MSG_TYPE_INTEGER_T,
-	    { MACH_MSG_TYPE_INTEGER_T, sizeof (integer_t) * 8, 1, 1, 0, 0 }
+	    .msgt_size = sizeof (integer_t) * 8,
+	    .msgt_number = 1,
+	    .msgt_inline = TRUE,
+	    .msgt_longform = FALSE,
+	    .msgt_deallocate = FALSE,
+	    .msgt_unused = 0
 	  };
 #endif
 
@@ -462,7 +460,7 @@ _hurd_select (int nfds,
 	      && msg.head.msgh_size >= sizeof msg.error
 	      && !(msg.head.msgh_bits & MACH_MSGH_BITS_COMPLEX)
 #ifdef MACH_MSG_TYPE_BIT
-	      && msg.error.err_type.word == inttype.word
+	      && !BAD_TYPECHECK (&msg.error.err_type, &inttype)
 #endif
 	      )
 	    {
@@ -480,7 +478,7 @@ _hurd_select (int nfds,
 		 occurred.  */
 	      if (msg.error.err
 #ifdef MACH_MSG_TYPE_BIT
-		  || msg.success.result_type.word != inttype.word
+		  || BAD_TYPECHECK (&msg.success.result_type, &inttype)
 #endif
 		  || msg.head.msgh_size != sizeof msg.success)
 		{

hurd/intr-msg.c

@@ -17,6 +17,7 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <mach.h>
+#include <mach_rpc.h>
 #include <mach/mig_errors.h>
 #include <mach/mig_support.h>
 #include <hurd/signal.h>
@@ -28,11 +29,6 @@
 # define mig_reply_header_t	mig_reply_error_t
 #endif
 
-/* Macro used by MIG to cleanly check the type.  */
-#define BAD_TYPECHECK(type, check) __glibc_unlikely (({	\
-  union { mach_msg_type_t t; uint32_t w; } _t, _c;	\
-  _t.t = *(type); _c.t = *(check);_t.w != _c.w; }))
-
 error_t
 _hurd_intr_rpc_mach_msg (mach_msg_header_t *msg,
 			 mach_msg_option_t option,

sysdeps/mach/hurd/ioctl.c

@@ -28,6 +28,7 @@
 #include <stdint.h>
 #include <hurd/ioctl.h>
 #include <mach/mig_support.h>
+#include <mach_rpc.h>
 #include <sysdep-cancel.h>
 
 #include <hurd/ioctls.defs>
@@ -35,11 +36,6 @@
 #define msg_align(x) ALIGN_UP (x, __alignof__ (uintptr_t))
 #define typesize(type)	(1 << (type))
 
-/* Macro used by MIG to cleanly check the type.  */
-#define BAD_TYPECHECK(type, check) __glibc_unlikely (({	\
-  union { mach_msg_type_t t; uint32_t w; } _t, _c;	\
-  _t.t = *(type); _c.t = *(check);_t.w != _c.w; }))
-
 /* Perform the I/O control operation specified by REQUEST on FD.
    The actual type and use of ARG and the return value depend on REQUEST.  */
 int

sysdeps/mach/mach_rpc.h

@@ -0,0 +1,30 @@
+/* Macros for handling Mach RPC messages.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <mach/message.h>
+
+/* Macro used by MIG to cleanly check the type.  */
+#define BAD_TYPECHECK(type, check) __glibc_unlikely (({	\
+  union { mach_msg_type_t t; uint32_t w; } _t, _c;	\
+  _t.t = *(type); _c.t = *(check);_t.w != _c.w; }))
+
+/* TODO: add this assertion for x86_64.  */
+#ifndef __x86_64__
+_Static_assert (sizeof (uint32_t) == sizeof (mach_msg_type_t),
+                "mach_msg_type_t needs to be the same size as uint32_t");
+#endif