[Blackfin] arch: This allows XIP to work with FD-PIC.

Previously, init failed to do anything meaningful;
it turns out that the reason is that FD-PIC has a readonly data
section which can be located in the XIP filesystem, and various address checks
in the kernel reject such addresses for syscall arguments.  Hence, init's
  execve ("/bin/sh", ...)
failed with error code EFAULT.

There's room for improvement here: in case people want to have filesystems
on flash rather than in main memory, _access_ok should be modified to
allow this.

This bug fix is also dedicated to Michael Hennerich.

Signed-off-by: Bernd Schmidt <bernds_cb1@t-online.de>
Signed-off-by: Bryan Wu <cooloney@kernel.org>

arch/blackfin/kernel/process.c

@@ -324,6 +324,12 @@ int _access_ok(unsigned long addr, unsigned long size)
 		return 1;
 	if (addr >= memory_mtd_end && (addr + size) <= physical_mem_end)
 		return 1;
+
+#ifdef CONFIG_ROMFS_MTD_FS
+	/* For XIP, allow user space to use pointers within the ROMFS.  */
+	if (addr >= memory_mtd_start && (addr + size) <= memory_mtd_end)
+		return 1;
+#endif
 #else
 	if (addr >= memory_start && (addr + size) <= physical_mem_end)
 		return 1;