microblaze_mmu_v2: entry.S, entry.h

Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/include/asm/entry.h

 /*
  * Definitions used by low-level trap handlers
  *
- * Copyright (C) 2008 Michal Simek
- * Copyright (C) 2007 - 2008 PetaLogix
+ * Copyright (C) 2008-2009 Michal Simek <monstr@monstr.eu>
+ * Copyright (C) 2007-2009 PetaLogix
  * Copyright (C) 2007 John Williams <john.williams@petalogix.com>
  *
  * This file is subject to the terms and conditions of the GNU General
@@ -31,7 +31,40 @@ DECLARE_PER_CPU(unsigned int, R11_SAVE); /* Temp variable for entry */
 DECLARE_PER_CPU(unsigned int, CURRENT_SAVE); /* Saved current pointer */
 # endif /* __ASSEMBLY__ */
 
+#ifndef CONFIG_MMU
+
 /* noMMU hasn't any space for args */
 # define STATE_SAVE_ARG_SPACE	(0)
 
+#else /* CONFIG_MMU */
+
+/* If true, system calls save and restore all registers (except result
+ * registers, of course).  If false, then `call clobbered' registers
+ * will not be preserved, on the theory that system calls are basically
+ * function calls anyway, and the caller should be able to deal with it.
+ * This is a security risk, of course, as `internal' values may leak out
+ * after a system call, but that certainly doesn't matter very much for
+ * a processor with no MMU protection!  For a protected-mode kernel, it
+ * would be faster to just zero those registers before returning.
+ *
+ * I can not rely on the glibc implementation. If you turn it off make
+ * sure that r11/r12 is saved in user-space. --KAA
+ *
+ * These are special variables using by the kernel trap/interrupt code
+ * to save registers in, at a time when there are no spare registers we
+ * can use to do so, and we can't depend on the value of the stack
+ * pointer.  This means that they must be within a signed 16-bit
+ * displacement of 0x00000000.
+ */
+
+/* A `state save frame' is a struct pt_regs preceded by some extra space
+ * suitable for a function call stack frame. */
+
+/* Amount of room on the stack reserved for arguments and to satisfy the
+ * C calling conventions, in addition to the space used by the struct
+ * pt_regs that actually holds saved values. */
+#define STATE_SAVE_ARG_SPACE	(6*4) /* Up to six arguments */
+
+#endif /* CONFIG_MMU */
+
 #endif /* _ASM_MICROBLAZE_ENTRY_H */