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SubjectRe: x86/entry vs kgdb
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.

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