On Thu, Apr 30, 2020 at 09:35:30AM -0700, Doug Anderson wrote: > Hi, > > On Thu, Apr 30, 2020 at 8:49 AM Daniel Thompson > <daniel.thompson@xxxxxxxxxx> wrote: > > > > On Tue, Apr 28, 2020 at 02:13:44PM -0700, Douglas Anderson wrote: > > > 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@xxxxxxxxxxxx> > > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > > > Cc: Borislav Petkov <bp@xxxxxxxxx> > > > Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > > > It looks like this patch is triggering some warnings from the existing > > defconfigs (both x86 and arm64). It looks like this: > > > > --- > > wychelm$ make defconfig > > GEN Makefile > > *** Default configuration is based on 'x86_64_defconfig' > > > > WARNING: unmet direct dependencies detected for ARCH_HAS_EARLY_DEBUG > > Depends on [n]: KGDB [=n] > > Selected by [y]: > > - X86 [=y] > > > > WARNING: unmet direct dependencies detected for ARCH_HAS_EARLY_DEBUG > > Depends on [n]: KGDB [=n] > > Selected by [y]: > > - X86 [=y] > > Ah, thanks! I hadn't noticed those. I think it'd be easy to just > change the relevant patches to just "select ARCH_HAS_EARLY_DEBUG if > KGDB". If you agree that's a good fix and are willing, I'd be happy > if you just added it to the relevant patches when applying. If not, I > can post a v4. Happy with the approach to fix this. Given the follow on discussion from the end of last week I suspect there probably needs to be a v4 anyway so perhaps the last question is applying a fix up is moot at this point? Daniel.
