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kgdb: Delay "kgdbwait" to dbg_late_init() by default

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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 select the
ARCH_HAS_EARLY_DEBUG KConfig option.  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_param'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>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20200507130644.v4.4.I3113aea1b08d8ce36dc3720209392ae8b815201b@changeid
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
This commit is contained in:
Douglas Anderson
2020-05-07 13:08:42 -07:00
committed by Daniel Thompson
parent 68e55f61c1
commit b1a57bbfcc
3 changed files with 34 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

25
kernel/debug/debug_core.c
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@@ -948,6 +948,14 @@ 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)
{
}
@@ -958,6 +966,9 @@ void __init dbg_late_init(void)
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
@@ -1053,14 +1064,6 @@ 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
@@ -1097,7 +1100,8 @@ 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 || IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG)))
kgdb_initial_breakpoint();
return 0;
@@ -1167,7 +1171,8 @@ 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 &&
IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG))
kgdb_initial_breakpoint();
return 0;