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x86,kgdb: Add low level debug hook

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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: Jason Wessel <jason.wessel@windriver.com>
This commit is contained in:
Jason Wessel 2010-05-20 21:04:25 -05:00
parent 98ec1878ca
commit f503b5ae53
6 changed files with 41 additions and 2 deletions
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3
arch/x86/include/asm/kgdb.h
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@ -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 */

22
arch/x86/kernel/kgdb.c
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@ -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)
{

6
arch/x86/kernel/traps.c
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@ -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)

1
include/linux/kgdb.h
View File

@ -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;

2
kernel/debug/debug_core.c
View File

@ -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;

9
lib/Kconfig.kgdb
View File

@ -57,6 +57,15 @@ config KGDB_TESTS_BOOT_STRING
information about other strings you could use beyond the
default of V1F100.
config KGDB_LOW_LEVEL_TRAP
bool "KGDB: Allow debugging with traps in notifiers"
depends on X86
default n
help
This will add an extra call back to kgdb for the breakpoint
exception handler on which will will allow kgdb to step
through a notify handler.
config KGDB_KDB
bool "KGDB_KDB: include kdb frontend for kgdb"
default n