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 <[email protected]> Signed-off-by: Jason Wessel <[email protected]> --- arch/x86/include/asm/kgdb.h | 3 +++ arch/x86/kernel/kgdb.c | 22 +++++++++++++++++++++- arch/x86/kernel/traps.c | 6 ++++++ include/linux/kgdb.h | 1 + kernel/debug/debug_core.c | 2 +- lib/Kconfig.kgdb | 9 +++++++++ 6 files changed, 41 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/kgdb.h b/arch/x86/include/asm/kgdb.h index e6c6c80..006da36 100644 --- a/arch/x86/include/asm/kgdb.h +++ b/arch/x86/include/asm/kgdb.h @@ -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 */ diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c index ce35f72..f4bf7a5 100644 --- a/arch/x86/kernel/kgdb.c +++ b/arch/x86/kernel/kgdb.c @@ -490,7 +490,7 @@ 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 */ @@ -498,6 +498,26 @@ 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) { diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 3339917..6ae2122 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -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> @@ -460,6 +461,11 @@ 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) diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h index 97ff1c5..f46d466 100644 --- a/include/linux/kgdb.h +++ b/include/linux/kgdb.h @@ -58,6 +58,7 @@ 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; diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c index 6a70e46..06e73e0 100644 --- a/kernel/debug/debug_core.c +++ b/kernel/debug/debug_core.c @@ -65,7 +65,7 @@ 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; diff --git a/lib/Kconfig.kgdb b/lib/Kconfig.kgdb index 0fb633c..2172c69 100644 --- a/lib/Kconfig.kgdb +++ b/lib/Kconfig.kgdb @@ -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 -- 1.6.4.rc1 ------------------------------------------------------------------------------ This SF.Net email is sponsored by the Verizon Developer Community Take advantage of Verizon's best-in-class app development support A streamlined, 14 day to market process makes app distribution fast and easy Join now and get one step closer to millions of Verizon customers http://p.sf.net/sfu/verizon-dev2dev _______________________________________________ Kgdb-bugreport mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/kgdb-bugreport
