On Wed, May 13, 2020 at 04:06:37PM -0700, Douglas Anderson wrote:
> A new kgdb feature will soon land (kgdb_earlycon) that lets us run
> kgdb much earlier. In order for everything to work properly it's
> important that the break hook is setup by the time we process
> "kgdbwait".
>
> Right now the break hook is setup in debug_traps_init() and that's
> called from arch_initcall(). That's a bit too late since
> kgdb_earlycon really needs things to be setup by the time the system
> calls dbg_late_init().
>
> We could fix this by adding call_break_hook() into early_brk64() and
> that works fine. However, it's a little ugly. Instead, let's just
> add a call to debug_traps_init() straight from trap_init(). There's
> already a documented dependency between trap_init() and
> debug_traps_init() and this makes the dependency more obvious rather
> than just relying on a comment.
>
> NOTE: this solution isn't early enough to let us select the
> "ARCH_HAS_EARLY_DEBUG" KConfig option that is introduced by the
> kgdb_earlycon patch series. That would only be set if we could do
> breakpoints when early params are parsed. This patch only enables
> "late early" breakpoints, AKA breakpoints when dbg_late_init() is
> called. It's expected that this should be fine for most people.
>
> It should also be noted that if you crash you can still end up in kgdb
> earlier than debug_traps_init(). Since you don't need breakpoints to
> debug a crash that's fine.
>
> Suggested-by: Will Deacon <w...@kernel.org>
> Signed-off-by: Douglas Anderson <diand...@chromium.org>
> Cc: Catalin Marinas <catalin.mari...@arm.com>
> Cc: Will Deacon <w...@kernel.org>
> ---
> This replaces the patch ("arm64: Add call_break_hook() to
> early_brk64() for early kgdb") in my recent kgdb series [1]. If I end
> up re-posting that series again I'll include this patch as a
> replacement, but I'm sending it separately to avoid spamming a pile of
> people another time with a 12-patch series.
>
> Note that, because it doesn't select the "ARCH_HAS_EARLY_DEBUG"
> KConfig option it could be landed standalone. However, it's still
> probably better to land together with that patch series.
>
> If the kgdb_earlycon patch series lands without this patch then
> kgdbwait + kgdb_earlycon won't work well on arm64, but there would be
> no other bad side effects.
>
> If this patch lands without the kgdb_earlycon patch series then there
> will be no known problems.
>
> [1]
> https://lore.kernel.org/r/20200507130644.v4.5.I22067ad43e77ddfd4b64c2d49030628480f9e8d9@changeid
>
> arch/arm64/include/asm/debug-monitors.h | 2 ++
> arch/arm64/kernel/debug-monitors.c | 4 +---
> arch/arm64/kernel/traps.c | 2 +-
> 3 files changed, 4 insertions(+), 4 deletions(-)
[...]
Acked-by: Will Deacon <w...@kernel.org>
I would prefer to take this via arm64, if possible, since we have quite lot
going in for 5.8, although I don't think this conflicts at the moment.
Daniel -- what do you want to do?
Will
