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    Subject[PATCH 19/25] mips,kgdb: kdb low level trap catch and stack trace
    Date
    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>
    ---
    arch/mips/include/asm/kgdb.h | 2 ++
    arch/mips/kernel/kgdb.c | 22 +++++++++++++++++++++-
    arch/mips/kernel/traps.c | 13 +++++++++++++
    lib/Kconfig.kgdb | 2 +-
    4 files changed, 37 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 6ed4c83..9b78ff6 100644
    --- a/arch/mips/kernel/kgdb.c
    +++ b/arch/mips/kernel/kgdb.c
    @@ -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,
    };
    diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
    index d612c6d..950bde8 100644
    --- a/arch/mips/kernel/traps.c
    +++ b/arch/mips/kernel/traps.c
    @@ -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;

    diff --git a/lib/Kconfig.kgdb b/lib/Kconfig.kgdb
    index c56ccb4..43cb93f 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
    + depends on X86 || MIPS
    default n
    help
    This will add an extra call back to kgdb for the breakpoint
    --
    1.6.3.3


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