powerpc/xmon: Setup debugger hooks when first break-point is set

Presently sysrq key for xmon('x') is registered during kernel init
irrespective of the value of kernel param 'xmon'. Thus xmon is enabled
even if 'xmon=off' is passed on the kernel command line. However this
doesn't enable the kernel debugger hooks needed for instruction or
data breakpoints. Thus when a break-point is hit with xmon=off a
kernel oops of the form below is reported:

  Oops: Exception in kernel mode, sig: 5 [#1]
  < snip >
  Trace/breakpoint trap

To fix this the patch checks and enables debugger hooks when an
instruction or data break-point is set via xmon console.

Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Reviewed-by: Balbir Singh <bsingharora@gmail.com>
[mpe: Just printf directly, no need for static const char[]]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 82e1a3e..ee4b607 100644 (file)
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -1273,6 +1273,16 @@ static long check_bp_loc(unsigned long addr)
        return 1;
 }
 
+/* Force enable xmon if not already enabled */
+static inline void force_enable_xmon(void)
+{
+       /* Enable xmon hooks if needed */
+       if (!xmon_on) {
+               printf("xmon: Enabling debugger hooks\n");
+               xmon_on = 1;
+       }
+}
+
 static char *breakpoint_help_string =
     "Breakpoint command usage:\n"
     "b                show breakpoints\n"
@@ -1315,6 +1325,8 @@ bpt_cmds(void)
                        dabr.address &= ~HW_BRK_TYPE_DABR;
                        dabr.enabled = mode | BP_DABR;
                }
+
+               force_enable_xmon();
                break;
 
        case 'i':       /* bi - hardware instr breakpoint */
@@ -1335,6 +1347,7 @@ bpt_cmds(void)
                if (bp != NULL) {
                        bp->enabled |= BP_CIABR;
                        iabr = bp;
+                       force_enable_xmon();
                }
                break;
 #endif
@@ -1399,8 +1412,10 @@ bpt_cmds(void)
                if (!check_bp_loc(a))
                        break;
                bp = new_breakpoint(a);
-               if (bp != NULL)
+               if (bp != NULL) {
                        bp->enabled |= BP_TRAP;
+                       force_enable_xmon();
+               }
                break;
        }
 }