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Subject[PATCH v2] xmon: Setup xmon debugger hooks when first break-point is set
Date
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>
---
Change-log:

v2 -> Moved the code that was force enabling xmon to a separate inline
function (Balbir)

The change related to clearing all breakpoints when xmon is
disabled via debugfs will be respinned as a separate
patch. (Mpe)
---
arch/powerpc/xmon/xmon.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 82e1a3ee6e0f..e9c7ec8f15f8 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -1273,6 +1273,18 @@ static long check_bp_loc(unsigned long addr)
return 1;
}

+/* Force enable xmon if not already enabled */
+static inline void force_enable_xmon(void)
+{
+ static const char warnxmon[] = "xmon: Enabling debugger hooks\n";
+
+ /* Enable xmon hooks if needed */
+ if (!xmon_on) {
+ printf(warnxmon);
+ xmon_on = 1;
+ }
+}
+
static char *breakpoint_help_string =
"Breakpoint command usage:\n"
"b show breakpoints\n"
@@ -1315,6 +1327,8 @@ 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 +1349,7 @@ bpt_cmds(void)
if (bp != NULL) {
bp->enabled |= BP_CIABR;
iabr = bp;
+ force_enable_xmon();
}
break;
#endif
@@ -1399,8 +1414,10 @@ 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;
}
}
--
2.14.3
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