Created attachment 189552 [details] [review]
Patch to fix double/guint64 alignment issue in gdbusmessage.c

GDBusMessage does not serialize/deserialize double values correctly on platforms with strict alignment constraints (in my particular case, ARM926EJ-S). For example:

GDBus-debug:Message:
  >>>> SENT D-Bus message (56 bytes)
  Type:    method-return
  Flags:   no-reply-expected
  Version: 0
  Serial:  34
  Headers:
    reply-serial -> uint32 2
    destination -> ':1.4'
    signature -> signature 'd'
  Body: (23.49853515625,)
  UNIX File Descriptors:
    (none)
  0000: 6c 02 01 01  08 00 00 00  22 00 00 00  1d 00 00 00    l.......".......
  0010: 08 01 67 00  01 64 00 00  05 01 75 00  02 00 00 00    ..g..d....u.....
  0020: 06 01 73 00  04 00 00 00  3a 31 2e 34  00 00 00 00    ..s.....:1.4....
  0030: 00 00 00 00  04 69 42 40      

Note that the body of the message is supposed to contain a double with a value of 23.49853515625 but is presented in the message's payload as '00 00 00 00 04 69 42 40' which equates to 36.8204.

See patch for offending code and solution. In summary, do not cast and de-reference a pointer from one type to another type with potentially different alignment constraints.