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Commit 5dd11d5d authored by Jason Wessel's avatar Jason Wessel
Browse files

mips,kgdb: kdb low level trap catch and stack trace 



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 to be 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: default avatarJason Wessel <jason.wessel@windriver.com>
Acked-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent ba797b28

arch/mips/include/asm/kgdb.h

+2 −0
Original line number Diff line number Diff line
@@ -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__ */

arch/mips/kernel/kgdb.c

+21 −1
Original line number Diff line number Diff line
@@ -203,7 +203,7 @@ 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))
@@ -217,6 +217,26 @@ 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,

};

arch/mips/kernel/traps.c

+13 −0
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ 
#include <linux/kgdb.h>

#include <linux/kdebug.h>

#include <linux/notifier.h>

#include <linux/kdb.h>



#include <asm/bootinfo.h>

#include <asm/branch.h>
@@ -185,6 +186,11 @@ 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 +366,8 @@ void __noreturn die(const char * str, 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);
@@ -704,6 +712,11 @@ 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;

lib/Kconfig.kgdb

+1 −1
Original line number Diff line number Diff line
@@ -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

       depends on X86 || MIPS

       default n

       help

         This will add an extra call back to kgdb for the breakpoint