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

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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 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: Jason Wessel <jason.wessel@windriver.com>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Jason Wessel 2010-05-20 21:04:26 -05:00
parent ba797b2813
commit 5dd11d5d47
4 changed files with 37 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/mips/include/asm/kgdb.h
View File

@ -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__ */

22
arch/mips/kernel/kgdb.c
View File

@ -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,
};

13
arch/mips/kernel/traps.c
View File

@ -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;

2
lib/Kconfig.kgdb
View File

@ -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