powerpc/xmon: Don't allow breakpoints on suffixes

Do not allow placing xmon breakpoints on the suffix of a prefix
instruction.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
[mpe: Don't split printf strings across lines]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200506034050.24806-27-jniethe5@gmail.com

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index ac8ccf3..d1a79f9 100644 (file)
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -889,8 +889,8 @@ static struct bpt *new_breakpoint(unsigned long a)
 static void insert_bpts(void)
 {
        int i;
-       struct ppc_inst instr;
-       struct bpt *bp;
+       struct ppc_inst instr, instr2;
+       struct bpt *bp, *bp2;
 
        bp = bpts;
        for (i = 0; i < NBPTS; ++i, ++bp) {
@@ -908,6 +908,29 @@ static void insert_bpts(void)
                        bp->enabled = 0;
                        continue;
                }
+               /*
+                * Check the address is not a suffix by looking for a prefix in
+                * front of it.
+                */
+               if (mread_instr(bp->address - 4, &instr2) == 8) {
+                       printf("Breakpoint at %lx is on the second word of a prefixed instruction, disabling it\n",
+                              bp->address);
+                       bp->enabled = 0;
+                       continue;
+               }
+               /*
+                * We might still be a suffix - if the prefix has already been
+                * replaced by a breakpoint we won't catch it with the above
+                * test.
+                */
+               bp2 = at_breakpoint(bp->address - 4);
+               if (bp2 && ppc_inst_prefixed(ppc_inst_read(bp2->instr))) {
+                       printf("Breakpoint at %lx is on the second word of a prefixed instruction, disabling it\n",
+                              bp->address);
+                       bp->enabled = 0;
+                       continue;
+               }
+
                patch_instruction(bp->instr, instr);
                patch_instruction((void *)bp->instr + ppc_inst_len(instr),
                                  ppc_inst(bpinstr));