[PATCH] ppc32: Simplified load string emulation error checking

The error checking for emulation of load string instructions was overly
generous and would cause certain valid forms of the instructions to be
treated as illegal.  We drop the range checking since the architecture
allows this to be boundedly undefined.  Tests on CPUs that support these
instructions appear not do cause illegal instruction traps on range errors
and just allow the execution to occur.

Thanks to Kim Phillips for debugging this and figuring out what real HW was
doing.
Signed-off-by: NKumar Gala <kumar.gala@freescale.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

arch/ppc/kernel/traps.c

@@ -408,12 +408,7 @@ static int emulate_string_inst(struct pt_regs *regs, u32 instword)
 
 	/* Early out if we are an invalid form of lswx */
 	if ((instword & INST_STRING_MASK) == INST_LSWX)
-		if ((rA >= rT) || (NB_RB >= rT) || (rT == rA) || (rT == NB_RB))
-			return -EINVAL;
-
-	/* Early out if we are an invalid form of lswi */
-	if ((instword & INST_STRING_MASK) == INST_LSWI)
-		if ((rA >= rT) || (rT == rA))
+		if ((rT == rA) || (rT == NB_RB))
 			return -EINVAL;
 
 	EA = (rA == 0) ? 0 : regs->gpr[rA];