[PATCH 1/3] kgdb,ppc: do not set kgdb_single_step on ppc

[PATCH 1/3] kgdb,ppc: do not set kgdb_single_step on ppc

[Tiejun Chen]

The kgdb_single_step flag has the possibility to indefinitely
hang the system on an SMP system.

The x86 arch have the same problem, and that problem was fixed by
commit 8097551d9ab9b9e3630(kgdb,x86: do not set kgdb_single_step
on x86). This patch does the same behaviors as x86's patch.

Signed-off-by: Dongdong Deng <dongdong.deng@windriver.com>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
---
 arch/powerpc/kernel/kgdb.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
index 782bd0a..bbabc5a 100644
--- a/arch/powerpc/kernel/kgdb.c
+++ b/arch/powerpc/kernel/kgdb.c
@@ -410,7 +410,6 @@ int kgdb_arch_handle_exception(int vector, int signo, int err_code,
 #else
 			linux_regs->msr |= MSR_SE;
 #endif
-			kgdb_single_step = 1;
 			atomic_set(&kgdb_cpu_doing_single_step,
 				   raw_smp_processor_id());
 		}
-- 
1.5.6

[PATCH 2/3] powerpc: Bail out of KGDB when we've been triggered

[Tiejun Chen]

We need to skip a breakpoint exception when it occurs after
a breakpoint has already been removed.

Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
---
 arch/powerpc/kernel/kgdb.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
index bbabc5a..e84252b 100644
--- a/arch/powerpc/kernel/kgdb.c
+++ b/arch/powerpc/kernel/kgdb.c
@@ -101,6 +101,24 @@ static int computeSignal(unsigned int tt)
 	return SIGHUP;		/* default for things we don't know about */
 }
 
+/**
+ *
+ *	kgdb_skipexception - Bail out of KGDB when we've been triggered.
+ *	@exception: Exception vector number
+ *	@regs: Current &struct pt_regs.
+ *
+ *	On some architectures we need to skip a breakpoint exception when
+ *	it occurs after a breakpoint has been removed.
+ *
+ */
+int kgdb_skipexception(int exception, struct pt_regs *regs)
+{
+	if (kgdb_isremovedbreak(regs->nip))
+		return 1;
+
+	return 0;
+}
+
 static int kgdb_call_nmi_hook(struct pt_regs *regs)
 {
 	kgdb_nmicallback(raw_smp_processor_id(), regs);
-- 
1.5.6

Re: [PATCH 2/3] powerpc: Bail out of KGDB when we've been triggered

[Tabi Timur-B04825]

On Wed, Aug 22, 2012 at 5:43 AM, Tiejun Chen <tiejun.chen@windriver.com> wrote:

> +int kgdb_skipexception(int exception, struct pt_regs *regs)
> +{
> +       if (kgdb_isremovedbreak(regs->nip))
> +               return 1;
> +
> +       return 0;
> +}

int kgdb_skipexception(int exception, struct pt_regs *regs)
{
        return !!kgdb_isremovedbreak(regs->nip));
}

If the caller only cares about zero vs. non-zero, you can drop the !!.

-- 
Timur Tabi
Linux kernel developer at Freescale

Re: [PATCH 2/3] powerpc: Bail out of KGDB when we've been triggered

[tiejun.chen]

On 08/22/2012 11:07 PM, Tabi Timur-B04825 wrote:
> On Wed, Aug 22, 2012 at 5:43 AM, Tiejun Chen <tiejun.chen@windriver.com> wrote:
> 
>> +int kgdb_skipexception(int exception, struct pt_regs *regs)
>> +{
>> +       if (kgdb_isremovedbreak(regs->nip))
>> +               return 1;
>> +
>> +       return 0;
>> +}
> 
> int kgdb_skipexception(int exception, struct pt_regs *regs)
> {
>         return !!kgdb_isremovedbreak(regs->nip));
> }
> 
> If the caller only cares about zero vs. non-zero, you can drop the !!.

Yes, so 'return kgdb_isremovedbreak(regs->nip);' is already fine and simple.

I'll update this as v2 so thanks your comment.

Tiejun

[PATCH 3/3] powerpc/kgdb: restore current_thread_info properly

[Tiejun Chen]

For powerpc BooKE and e200, singlestep is handled on the critical/dbg
exception stack. This causes current_thread_info() to fail for kgdb
internal, so previously We work around this issue by copying
the thread_info from the kernel stack before calling kgdb_handle_exception,
and copying it back afterwards.

But actually we don't do this previously. We should backp current_thread_info
then restore that when exit.

CC: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
---
 arch/powerpc/kernel/kgdb.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
index e84252b..7dcdbe7 100644
--- a/arch/powerpc/kernel/kgdb.c
+++ b/arch/powerpc/kernel/kgdb.c
@@ -25,6 +25,7 @@
 #include <asm/processor.h>
 #include <asm/machdep.h>
 #include <asm/debug.h>
+#include <linux/slab.h>
 
 /*
  * This table contains the mapping between PowerPC hardware trap types, and
@@ -156,6 +157,8 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
 static int kgdb_singlestep(struct pt_regs *regs)
 {
 	struct thread_info *thread_info, *exception_thread_info;
+	struct thread_info *backup_current_thread_info = \
+		(struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
 
 	if (user_mode(regs))
 		return 0;
@@ -173,13 +176,17 @@ static int kgdb_singlestep(struct pt_regs *regs)
 	thread_info = (struct thread_info *)(regs->gpr[1] & ~(THREAD_SIZE-1));
 	exception_thread_info = current_thread_info();
 
-	if (thread_info != exception_thread_info)
+	if (thread_info != exception_thread_info) {
+		/* Save the original current_thread_info. */
+		memcpy(backup_current_thread_info, exception_thread_info, sizeof *thread_info);
 		memcpy(exception_thread_info, thread_info, sizeof *thread_info);
+	}
 
 	kgdb_handle_exception(0, SIGTRAP, 0, regs);
 
 	if (thread_info != exception_thread_info)
-		memcpy(thread_info, exception_thread_info, sizeof *thread_info);
+		/* Restore current_thread_info lastly. */
+		memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info);
 
 	return 1;
 }
-- 
1.5.6