@@ -673,6 +673,11 @@ void kgdb_arch_late(void)
}
}
+bool kgdb_arch_can_debug_early(void)
+{
+ return true;
+}
+
/**
* kgdb_arch_exit - Perform any architecture specific uninitalization.
*
@@ -226,6 +226,28 @@ extern int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt);
*/
extern void kgdb_arch_late(void);
+/**
+ * kgdb_arch_can_debug_early - Check if OK to break before dbg_late_init()
+ *
+ * If an architecture can definitely handle entering the debugger when
+ * early_param's are parsed then it can override this function to return
+ * true. Otherwise if "kgdbwait" is passed on the kernel command line it
+ * won't actually be processed until dbg_late_init() just after the call
+ * to kgdb_arch_late() is made.
+ *
+ * NOTE: Even if this returns false we will still try to register kgdb to
+ * handle breakpoints and crashes when early_params's are parsed, we just
+ * won't act on the "kgdbwait" parameter until dbg_late_init(). If you
+ * get a crash and try to drop into kgdb somewhere between these two
+ * places you might or might not end up being able to use kgdb depending
+ * on exactly how far along the architecture has initted.
+ *
+ * ALSO: dbg_late_init() is actually still fairly early in the system
+ * boot process.
+ *
+ * Return: true if platform can handle kgdb early.
+ */
+extern bool kgdb_arch_can_debug_early(void);
/**
* struct kgdb_arch - Describe architecture specific values.
@@ -950,16 +950,32 @@ void kgdb_panic(const char *msg)
kgdb_breakpoint();
}
+static void kgdb_initial_breakpoint(void)
+{
+ kgdb_break_asap = 0;
+
+ pr_crit("Waiting for connection from remote gdb...\n");
+ kgdb_breakpoint();
+}
+
void __weak kgdb_arch_late(void)
{
}
+bool __weak kgdb_arch_can_debug_early(void)
+{
+ return false;
+}
+
void __init dbg_late_init(void)
{
dbg_is_early = false;
if (kgdb_io_module_registered)
kgdb_arch_late();
kdb_init(KDB_INIT_FULL);
+
+ if (kgdb_io_module_registered && kgdb_break_asap)
+ kgdb_initial_breakpoint();
}
static int
@@ -1055,14 +1071,6 @@ void kgdb_schedule_breakpoint(void)
}
EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
-static void kgdb_initial_breakpoint(void)
-{
- kgdb_break_asap = 0;
-
- pr_crit("Waiting for connection from remote gdb...\n");
- kgdb_breakpoint();
-}
-
/**
* kgdb_register_io_module - register KGDB IO module
* @new_dbg_io_ops: the io ops vector
@@ -1099,7 +1107,8 @@ int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
/* Arm KGDB now. */
kgdb_register_callbacks();
- if (kgdb_break_asap)
+ if (kgdb_break_asap &&
+ (!dbg_is_early || kgdb_arch_can_debug_early()))
kgdb_initial_breakpoint();
return 0;
@@ -1169,7 +1178,7 @@ static int __init opt_kgdb_wait(char *str)
kgdb_break_asap = 1;
kdb_init(KDB_INIT_EARLY);
- if (kgdb_io_module_registered)
+ if (kgdb_io_module_registered && kgdb_arch_can_debug_early())
kgdb_initial_breakpoint();
return 0;
Using kgdb requires at least some level of architecture-level initialization. If nothing else, it relies on the architecture to pass breakpoints / crashes onto kgdb. On some architectures this all works super early, specifically it starts working at some point in time before Linux parses early_params's. On other architectures it doesn't. A survey of a few platforms: a) x86: Presumably it all works early since "ekgdboc" is documented to work here. b) arm64: Catching crashes works; with a simple patch breakpoints can also be made to work. c) arm: Nothing in kgdb works until paging_init() -> devicemaps_init() -> early_trap_init() Let's be conservative and, by default, process "kgdbwait" (which tells the kernel to drop into the debugger ASAP at boot) a bit later at dbg_late_init() time. If an architecture has tested it and wants to re-enable super early debugging, they can implement the weak function kgdb_arch_can_debug_early() to return true. We'll do this for x86 to start. It should be noted that dbg_late_init() is still called quite early in the system. Note that this patch doesn't affect when kgdb runs its init. If kgdb is set to initialize early it will still initialize when parsing early_params's. This patch _only_ inhibits the initial breakpoint from "kgdbwait". This means: * Without any extra patches arm64 platforms will at least catch crashes after kgdb inits. * arm platforms will catch crashes (and could handle a hardcoded kgdb_breakpoint()) any time after early_trap_init() runs, even before dbg_late_init(). Signed-off-by: Douglas Anderson <dianders@chromium.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> --- Changes in v2: None arch/x86/kernel/kgdb.c | 5 +++++ include/linux/kgdb.h | 22 ++++++++++++++++++++++ kernel/debug/debug_core.c | 29 +++++++++++++++++++---------- 3 files changed, 46 insertions(+), 10 deletions(-)