powerpc/xmon: Use a function for reading instructions

Currently in xmon, mread() is used for reading instructions. In
preparation for prefixed instructions, create and use a new function,
mread_instr(), especially for reading instructions.
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Alistair Popple <alistair@popple.id.au>
Link: https://lore.kernel.org/r/20200506034050.24806-19-jniethe5@gmail.com

arch/powerpc/xmon/xmon.c

@@ -122,6 +122,7 @@ static unsigned bpinstr = 0x7fe00008;	/* trap */
 static int cmds(struct pt_regs *);
 static int mread(unsigned long, void *, int);
 static int mwrite(unsigned long, void *, int);
+static int mread_instr(unsigned long, struct ppc_inst *);
 static int handle_fault(struct pt_regs *);
 static void byterev(unsigned char *, int);
 static void memex(void);
@@ -896,7 +897,7 @@ static void insert_bpts(void)
 	for (i = 0; i < NBPTS; ++i, ++bp) {
 		if ((bp->enabled & (BP_TRAP|BP_CIABR)) == 0)
 			continue;
-		if (mread(bp->address, &instr, 4) != 4) {
+		if (!mread_instr(bp->address, &instr)) {
 			printf("Couldn't read instruction at %lx, "
 			       "disabling breakpoint there\n", bp->address);
 			bp->enabled = 0;
@@ -946,7 +947,7 @@ static void remove_bpts(void)
 	for (i = 0; i < NBPTS; ++i, ++bp) {
 		if ((bp->enabled & (BP_TRAP|BP_CIABR)) != BP_TRAP)
 			continue;
-		if (mread(bp->address, &instr, 4) == 4
+		if (mread_instr(bp->address, &instr)
 		    && ppc_inst_equal(instr, ppc_inst(bpinstr))
 		    && patch_instruction(
 			(struct ppc_inst *)bp->address, ppc_inst_read(bp->instr)) != 0)
@@ -1162,7 +1163,7 @@ static int do_step(struct pt_regs *regs)
 	force_enable_xmon();
 	/* check we are in 64-bit kernel mode, translation enabled */
 	if ((regs->msr & (MSR_64BIT|MSR_PR|MSR_IR)) == (MSR_64BIT|MSR_IR)) {
-		if (mread(regs->nip, &instr, 4) == 4) {
+		if (mread_instr(regs->nip, &instr)) {
 			stepped = emulate_step(regs, instr);
 			if (stepped < 0) {
 				printf("Couldn't single-step %s instruction\n",
@@ -1329,7 +1330,7 @@ static long check_bp_loc(unsigned long addr)
 		printf("Breakpoints may only be placed at kernel addresses\n");
 		return 0;
 	}
-	if (!mread(addr, &instr, sizeof(instr))) {
+	if (!mread_instr(addr, &instr)) {
 		printf("Can't read instruction at address %lx\n", addr);
 		return 0;
 	}
@@ -2122,6 +2123,25 @@ mwrite(unsigned long adrs, void *buf, int size)
 	return n;
 }
 
+static int
+mread_instr(unsigned long adrs, struct ppc_inst *instr)
+{
+	volatile int n;
+
+	n = 0;
+	if (setjmp(bus_error_jmp) == 0) {
+		catch_memory_errors = 1;
+		sync();
+		*instr = ppc_inst_read((struct ppc_inst *)adrs);
+		sync();
+		/* wait a little while to see if we get a machine check */
+		__delay(200);
+		n = ppc_inst_len(*instr);
+	}
+	catch_memory_errors = 0;
+	return n;
+}
+
 static int fault_type;
 static int fault_except;
 static char *fault_chars[] = { "--", "**", "##" };