[ubuntu-mono] [Bug 122496] Re: mono always crashes on ppc

Alessandro Decina alessandro at nnva.org
Fri Jul 13 17:50:41 BST 2007

The ndesk segfault is due to an inconsistency in how structs are passed
in pinvoke. On ppc structs are always passed by-address. This is how
GIOChannel is wrapped in ndesk-glib:

	struct IOChannel
		const string GLIB = "libglib-2.0-0.dll";

                public IntPtr Handle;

			static extern IntPtr g_io_channel_unix_new (int fd);
		public IOChannel (int fd)
			Handle = g_io_channel_unix_new (fd);

Then g_io_add_watch is defined as a pinvoke method:

			protected static extern uint g_io_add_watch (IOChannel channel, IOCondition condition, IOFunc func, IntPtr user_data);

The g_io_add_watch wrapper takes a IOChannel structure as its first argument. The real g_io_add_watch takes a GIOChannel * argument as first argument.
On x86 this works because IOChannel is passed by value, so the GIOChannel * pointer in the real g_io_add_watch gets the value of IOChannel::Handle which points to the right location.
On ppc IOChannel is passed by address, so the GIOChannel * pointer in the real g_io_add_watch gets *a pointer* to IOChannel::Handle.

setting PPC_PASS_STRUCTS_BY_VALUE to 1 in mono/mini/mini-ppc.h and
recompiling fixes the bug here. Anyway i don't know  why it is set to 0
by default and if changing it has any drawbacks.

mono always crashes on ppc
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