On Mon, May 25, 2020 at 11:18:32AM +0200, Peter Zijlstra wrote: > On Mon, May 25, 2020 at 10:36:05AM +0200, Peter Zijlstra wrote: > > Hi! > > > > Since you seem to care about kgdb, I figured you might want to fix this > > before I mark it broken on x86 (we've been considering doing that for a > > while). > > > > AFAICT the whole debugreg usage of kgdb-x86_64 is completely hosed; it > > doesn't respsect the normal exclusion zones as per arch_build_bp_info(). > > > > That is, breakpoints must never be in: > > > > - in the cpu_entry_area > > - in .entry.text > > - in .noinstr.text > > - in anything else marked NOKPROBE > > > > by not respecting these constraints it is trivial to completely and > > utterly hose the machine. The entry rework that is current underway will > > explicitly not deal with #DB triggering in any of those places. > > This also very much includes single stepping those bits. Which KGDB > obviously also does not respects.
For breakpoints there's already a pre-poke validation hook that architectures can override if they want to. I can modify the default implementation to include checking the nokprobe list. Stepping is a bit more complex. There are hooks for some of the underlying work but not pre-step validation hook. I'll see if we can add one. Daniel.
