Align mach_msg_type_t and mach_msg_type_long_t with the same alignment as uintptr_t.

With this change, any 64 bit code using the IPC subsystem without relying on
MiG will work without any changes. We have a few examples of this inside gnumach but
also in the Hurd servers. For example, in hurd/console/display.c

  typedef struct
  {
    mach_msg_header_t Head;
    mach_msg_type_t ticknoType;
    natural_t tickno;
    mach_msg_type_t changeType;
    file_changed_type_t change;
    mach_msg_type_t startType;
    loff_t start;
    mach_msg_type_t endType;
    loff_t end;
  } Request;

This will now work correctly in 64 bits, without requiring any explicit padding.

As a follow up, we can simplify mach_msg_type_long_t so that we
only need an 8 byte structure where the second field will include the
number of elements for the long form. This is already included in
mach_msg_type_t as unused_msgtl_number.
Message-Id: <ZAbhOfOzsb8qPFs6@jupiter.tail36e24.ts.net>

1 files changed, 7 insertions, 7 deletions

diff --git a/include/mach/message.h b/include/mach/message.h
index 22a17b03..0eab9d41 100644
--- a/include/mach/message.h
+++ b/include/mach/message.h
@@ -132,9 +132,6 @@ typedef	unsigned int mach_msg_size_t;
 typedef natural_t mach_msg_seqno_t;
 typedef integer_t mach_msg_id_t;
 
-/* Force 4-byte alignment to simplify how the kernel parses the messages */
-#pragma pack(push, 4)
-
 /* full header structure, may have different size in user/kernel spaces */
 typedef	struct mach_msg_header {
     mach_msg_bits_t	msgh_bits;
@@ -232,16 +229,19 @@ typedef struct  {
 			msgt_longform : 1,
 			msgt_deallocate : 1,
 			msgt_unused : 1;
-} mach_msg_type_t;
+#ifdef __x86_64__
+    /* TODO: We want to eventually use this in favor of mach_msg_type_long_t
+     * as it makes the mach_msg protocol require only mach_msg_type_t. */
+    mach_msg_type_number_t   unused_msgtl_number;
+#endif
+} __attribute__ ((aligned (__alignof__ (uintptr_t)))) mach_msg_type_t;
 
 typedef	struct	{
     mach_msg_type_t	msgtl_header;
     unsigned short	msgtl_name;
     unsigned short	msgtl_size;
     natural_t		msgtl_number;
-} mach_msg_type_long_t;
-
-#pragma pack(pop)
+} __attribute__ ((aligned (__alignof__ (uintptr_t)))) mach_msg_type_long_t;
 
 /*
  *	Known values for the msgt_name field.