[PATCH v2] powerpc/xmon: Also setup debugger hooks when single-stepping

[PATCH v2] powerpc/xmon: Also setup debugger hooks when single-stepping

[Michal Suchanek]

When single-stepping kernel code from xmon without a debug hook enabled
the kernel crashes. This can happen when kernel starts with xmon on
crash disabled but xmon is entered using sysrq.

Call force_enable_xmon when single-stepping in xmon to install the xmon
debug hooks.

Fixes: e1368d0c9edb ("powerpc/xmon: Setup debugger hooks when first
break-point is set")

Signed-off-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/xmon/xmon.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

v2: calling force_enable_xmon in do_step is sufficient

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index a0842f1ff72c..252df9741d20 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -778,6 +778,16 @@ static int xmon_fault_handler(struct pt_regs *regs)
 	return 0;
 }
 
+/* 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 struct bpt *at_breakpoint(unsigned long pc)
 {
 	int i;
@@ -1094,6 +1104,7 @@ static int do_step(struct pt_regs *regs)
 	unsigned int instr;
 	int stepped;
 
+	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) {
@@ -1268,16 +1279,6 @@ 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"
-- 
2.13.6

Re: [PATCH v2] powerpc/xmon: Also setup debugger hooks when single-stepping

[Vaibhav Jain]

Michal Suchanek <msuchanek@suse.de> writes:

> When single-stepping kernel code from xmon without a debug hook enabled
> the kernel crashes. This can happen when kernel starts with xmon on
> crash disabled but xmon is entered using sysrq.
>
> Call force_enable_xmon when single-stepping in xmon to install the xmon
> debug hooks.
>
> Fixes: e1368d0c9edb ("powerpc/xmon: Setup debugger hooks when first
> break-point is set")
>
> Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> ---
LGTM,

Reviewed-by: Vaibhav Jain <vaibhav@linux.ibm.com>

-- 
Vaibhav Jain <vaibhav@linux.ibm.com>
Linux Technology Center, IBM India Pvt. Ltd.

Re: [v2] powerpc/xmon: Also setup debugger hooks when single-stepping

[Michael Ellerman]

On Wed, 2018-05-23 at 18:00:54 UTC, Michal Suchanek wrote:
> When single-stepping kernel code from xmon without a debug hook enabled
> the kernel crashes. This can happen when kernel starts with xmon on
> crash disabled but xmon is entered using sysrq.
> 
> Call force_enable_xmon when single-stepping in xmon to install the xmon
> debug hooks.
> 
> Fixes: e1368d0c9edb ("powerpc/xmon: Setup debugger hooks when first
> break-point is set")
> 
> Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> Reviewed-by: Vaibhav Jain <vaibhav@linux.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/7daf59300999693b85233762b847f1

cheers