Richard Braun, le Mon 02 Apr 2012 12:03:34 +0200, a écrit : > On Sun, Apr 01, 2012 at 05:45:19PM +0200, Samuel Thibault wrote: > > I don't really see why there should be a "size of a pointer" property > > anyway: AIUI, vm_offset_t and vm_size_t are there for that. I rather > > see natural_t and integer_t as a "nice integer" type, i.e. something > > that can hold big enough values (e.g. >32bit), but not too big either > > (there is usually no point in having 64bit values), and thus the int > > type is "just fine". It is currently essentially used in RPCs to provide > > statistics, and for the RPC mechanism itself. > > Kernel port names are addresses of their target IPC port object.
Inside the kernel, yes. In the userland processes, no. That's the difference that xnu makes between mach_port_t (kernelland) and mach_port_name_t (userland) (sorry I forgot to mention that in my previous mail). > As > a simple solution, the kernel allocator could be tuned to return only > low addresses, so that natural_t could remain 32-bits (since userspace > is 32-bits), and keep the optmization inside the kernel. We can also rather simply fix the code that converts from names to pointers into using different sizes, like xnu does. > > - The actual RPC mechanism however needs some decisions, notably the > > mach_port_t type. For now it is a vm_offset_t type, and the kernel > > ipc mechanism will assume pointer alignment. Of course, 32bit userland > > will use a 32bit type and 32bit alignment there, so conversion will > > be needed. I've however noticed that there, xnu also simply used the > > natural_t type for port numbers, which is thus the same for 32 and 64bit > > builds, and saves a lot of headaches. I guess we don't really really > > need >2^32 ports anyway, so wouldn't it make sense to use a 32bit type > > too for a 64bit port? > > I guess it's the preferable way. I'm not sure Xnu "chose" anything > there, as port names were early intended to be natural_t (because of > the optimization described above). They decided to split mach_port_t into mach_port_t and mach_port_name_t, and cope with the size difference. Samuel
