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Subject[PATCH 10/13] RFC ONLY - mips,kgdb: kdb low level trap catch and stack trace
Date
This is a RFC patch.  The work to possibly merge kdb and kgdb is being
evaluated and this patch is considered only a proof of concept or
prototype.

The only way the debugger can handle a trap in inside rcu_lock,
notify_die, or atomic_notifier_call_chain without a recursive fault is
to have a low level "first opportunity handler" do_trap_or_bp() handler.

Generally this will be something the vast majority of folks will not
need, but for those who need it, it is added as a kernel .config
option called KGDB_LOW_LEVEL_TRAP.

Also added was a die notification for oops such that kdb can catch an
oops for analysis.

There appeared no obvious way to pass the struct pt_regs from the
original exception back to the stack back tracer, so a special case was
added to show_stack() for when kdb is active because you generally
desire to generally look at the back trace of the original exception.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
---
arch/mips/include/asm/kgdb.h | 2 ++
arch/mips/kernel/kgdb.c | 22 +++++++++++++++++++++-
arch/mips/kernel/traps.c | 14 ++++++++++++++
lib/Kconfig.kgdb | 2 +-
4 files changed, 38 insertions(+), 2 deletions(-)
diff --git a/arch/mips/include/asm/kgdb.h b/arch/mips/include/asm/kgdb.h
index 48223b0..19002d6 100644
--- a/arch/mips/include/asm/kgdb.h
+++ b/arch/mips/include/asm/kgdb.h
@@ -38,6 +38,8 @@ extern int kgdb_early_setup;
extern void *saved_vectors[32];
extern void handle_exception(struct pt_regs *regs);
extern void breakinst(void);
+extern int kgdb_ll_trap(int cmd, const char *str,
+ struct pt_regs *regs, long err, int trap, int sig);

#endif /* __KERNEL__ */

diff --git a/arch/mips/kernel/kgdb.c b/arch/mips/kernel/kgdb.c
index 54f2d40..a4e546a 100644
--- a/arch/mips/kernel/kgdb.c
+++ b/arch/mips/kernel/kgdb.c
@@ -202,7 +202,7 @@ static int kgdb_mips_notify(struct notifier_block *self, unsigned long cmd,
if (atomic_read(&kgdb_active) != -1)
kgdb_nmicallback(smp_processor_id(), regs);

- if (kgdb_handle_exception(trap, compute_signal(trap), 0, regs))
+ if (kgdb_handle_exception(trap, compute_signal(trap), cmd, regs))
return NOTIFY_DONE;

if (atomic_read(&kgdb_setting_breakpoint))
@@ -216,6 +216,26 @@ static int kgdb_mips_notify(struct notifier_block *self, unsigned long cmd,
return NOTIFY_STOP;
}

+#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
+int kgdb_ll_trap(int cmd, const char *str,
+ struct pt_regs *regs, long err, int trap, int sig)
+{
+ struct die_args args = {
+ .regs = regs,
+ .str = str,
+ .err = err,
+ .trapnr = trap,
+ .signr = sig,
+
+ };
+
+ if (!kgdb_io_module_registered)
+ return NOTIFY_DONE;
+
+ return kgdb_mips_notify(NULL, cmd, &args);
+}
+#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */
+
static struct notifier_block kgdb_notifier = {
.notifier_call = kgdb_mips_notify,
};
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index e83da17..fbf427e 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -24,6 +24,8 @@
#include <linux/interrupt.h>
#include <linux/ptrace.h>
#include <linux/kgdb.h>
+#include <linux/kdb.h>
+#include <linux/kdbprivate.h>
#include <linux/kdebug.h>

#include <asm/bootinfo.h>
@@ -186,6 +188,11 @@ void show_stack(struct task_struct *task, unsigned long *sp)
regs.regs[29] = task->thread.reg29;
regs.regs[31] = 0;
regs.cp0_epc = task->thread.reg31;
+#ifdef CONFIG_KGDB_KDB
+ } else if (atomic_read(&kgdb_active) != -1 &&
+ kdb_current_regs) {
+ memcpy(&regs, kdb_current_regs, sizeof(regs));
+#endif /* CONFIG_KGDB_KDB */
} else {
prepare_frametrace(&regs);
}
@@ -360,6 +367,8 @@ void __noreturn die(const char * str, const struct pt_regs * regs)
unsigned long dvpret = dvpe();
#endif /* CONFIG_MIPS_MT_SMTC */

+ notify_die(DIE_OOPS, str, (struct pt_regs *)regs, SIGSEGV, 0, 0);
+
console_verbose();
spin_lock_irq(&die_lock);
bust_spinlocks(1);
@@ -701,6 +710,11 @@ static void do_trap_or_bp(struct pt_regs *regs, unsigned int code,
siginfo_t info;
char b[40];

+#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
+ if (kgdb_ll_trap(DIE_TRAP, str, regs, code, 0, 0) == NOTIFY_STOP)
+ return;
+#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */
+
if (notify_die(DIE_TRAP, str, regs, code, 0, 0) == NOTIFY_STOP)
return;

diff --git a/lib/Kconfig.kgdb b/lib/Kconfig.kgdb
index a2f63be..b5d3637 100644
--- a/lib/Kconfig.kgdb
+++ b/lib/Kconfig.kgdb
@@ -59,7 +59,7 @@ config KGDB_TESTS_BOOT_STRING

config KGDB_LOW_LEVEL_TRAP
bool "KGDB: Allow debugging with traps in notifiers"
- depends on X86 || PPC
+ depends on X86 || PPC || MIPS
default n
help
This will add an extra call back to kgdb for the breakpoint
--
1.6.3.rc0.1.gf800


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