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Commit f503b5ae authored by Jason Wessel's avatar Jason Wessel
Browse files

x86,kgdb: Add low level debug hook 



The only way the debugger can handle a trap in inside rcu_lock,
notify_die, or atomic_notifier_call_chain without a triple fault is
to have a low level "first opportunity handler" in the int3 exception
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.

CC: Ingo Molnar <mingo@elte.hu>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: H. Peter Anvin <hpa@zytor.com>
CC: x86@kernel.org
Signed-off-by: default avatarJason Wessel <jason.wessel@windriver.com>
parent 98ec1878

arch/x86/include/asm/kgdb.h

+3 −0
Original line number Diff line number Diff line
@@ -76,4 +76,7 @@ static inline void arch_kgdb_breakpoint(void) 
#define BREAK_INSTR_SIZE	1

#define CACHE_FLUSH_IS_SAFE	1



extern int kgdb_ll_trap(int cmd, const char *str,

			struct pt_regs *regs, long err, int trap, int sig);



#endif /* _ASM_X86_KGDB_H */

arch/x86/kernel/kgdb.c

+21 −1
Original line number Diff line number Diff line
@@ -538,7 +538,7 @@ static int __kgdb_notify(struct die_args *args, unsigned long cmd) 
			return NOTIFY_DONE;

	}



	if (kgdb_handle_exception(args->trapnr, args->signr, args->err, regs))

	if (kgdb_handle_exception(args->trapnr, args->signr, cmd, regs))

		return NOTIFY_DONE;



	/* Must touch watchdog before return to normal operation */
@@ -546,6 +546,26 @@ static int __kgdb_notify(struct die_args *args, 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_notify(&args, cmd);

}

#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */



static int

kgdb_notify(struct notifier_block *self, unsigned long cmd, void *ptr)

{

arch/x86/kernel/traps.c

+6 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include <linux/kprobes.h>

#include <linux/uaccess.h>

#include <linux/kdebug.h>

#include <linux/kgdb.h>

#include <linux/kernel.h>

#include <linux/module.h>

#include <linux/ptrace.h>
@@ -451,6 +452,11 @@ void restart_nmi(void) 
/* May run on IST stack. */

dotraplinkage void __kprobes do_int3(struct pt_regs *regs, long error_code)

{

#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP

	if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, 3, SIGTRAP)

			== NOTIFY_STOP)

		return;

#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */

#ifdef CONFIG_KPROBES

	if (notify_die(DIE_INT3, "int3", regs, error_code, 3, SIGTRAP)

			== NOTIFY_STOP)

include/linux/kgdb.h

+1 −0
Original line number Diff line number Diff line
@@ -60,6 +60,7 @@ struct uart_port; 
void kgdb_breakpoint(void);



extern int kgdb_connected;

extern int kgdb_io_module_registered;



extern atomic_t			kgdb_setting_breakpoint;

extern atomic_t			kgdb_cpu_doing_single_step;

kernel/debug/debug_core.c

+1 −1
Original line number Diff line number Diff line
@@ -66,7 +66,7 @@ int kgdb_connected; 
EXPORT_SYMBOL_GPL(kgdb_connected);



/* All the KGDB handlers are installed */

static int			kgdb_io_module_registered;

int			kgdb_io_module_registered;



/* Guard for recursive entry */

static int			exception_level;