Re: [PATCH V3 2/6] arm64: kgdb_step_brk_fn: ignore other's exception

From: Pratyush Anand
Date: Wed Nov 02 2016 - 06:16:25 EST

On Wednesday 02 November 2016 03:30 PM, Sandeepa Prabhu wrote:

On Wed, Nov 2, 2016 at 2:40 PM, Pratyush Anand <panand@xxxxxxxxxx
<mailto:panand@xxxxxxxxxx>> wrote:

ARM64 step exception does not have any syndrome information. So, it is
responsibility of exception handler to take care that they handle it
only if exception was raised for them.

Since kgdb_step_brk_fn() always returns 0, therefore we might have
when we will have other step handler registered as well.

This patch fixes kgdb_step_brk_fn() to return error in case of step
was not meant for kgdb.

Signed-off-by: Pratyush Anand <panand@xxxxxxxxxx
arch/arm64/kernel/kgdb.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
index e017a9493b92..d217c9e95b06 100644
--- a/arch/arm64/kernel/kgdb.c
+++ b/arch/arm64/kernel/kgdb.c
@@ -247,6 +247,9 @@ NOKPROBE_SYMBOL(kgdb_compiled_brk_fn);

static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr)
+ if (!kgdb_single_step)
+ return DBG_HOOK_ERROR;

âThis is needed. So, single stepping in kprobes working all these days
because kprobes handler was registered earlier to kgdb handler!â

Actually kprobe_single_step_handler() is not called through call_step_hook(), so it is always safe.

We had discussed here ( that why we can not register kprobe_single_step_handler() via register_set_hook()
and only invoke call_step_hook().