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] # # No change to .config # --- Daniel.
