powerpc: handle unaligned ldbrx/stdbrx

Normally when we haven't implemented an alignment handler for a load or store instruction the process will be terminated.

The alignment handler uses the DSISR (or a pseudo one) to locate the right handler. Unfortunately ldbrx and stdbrx overlap lfs and stfs so we incorrectly think ldbrx is an lfs and stdbrx is an stfs.

This bug is particularly nasty - instead of terminating the process we apply an incorrect fixup and continue on.

With more and more overlapping instructions we should stop creating a pseudo DSISR and index using the instruction directly, but for now add a special case to catch ldbrx/stdbrx.

---

Index: b/arch/powerpc/kernel/align.c
===================================================================
@@ -764,6 +764,16 @@ int fix_alignment(struct pt_regs *regs)
 	nb = aligninfo[instr].len;
 	flags = aligninfo[instr].flags;
 
+	/* ldbrx/stdbrx overlap lfs/stfs in the DSISR unfortunately */
+	if (IS_XFORM(instruction) && ((instruction >> 1) & 0x3ff) == 532) {
+		nb = 8;
+		flags = LD+SW;
+	} else if (IS_XFORM(instruction) &&
+		   ((instruction >> 1) & 0x3ff) == 660) {
+		nb = 8;
+		flags = ST+SW;
+	}
+
 	/* Byteswap little endian loads and stores */
 	swiz = 0;
 	if (regs->msr & MSR_LE) {

Hi Anton,

Cheers,
Stephen Rothwell                    [email protected]