[PATCH 1/4] xkb: LockMods can lock another group on key release #865

[wettstein509 at solnet.ch]

> * where are the bytes guaranteed to be zero? Not questioning, I just want to
>   double-check and it's outside the patch contexts

I looked into xkbcomp source.  Before the actions structs are written to
according to the specification in the .xkb file, they are indeed zeroed.
For specifications in xkb_symbols (symbols.c), this is done by a call to
uTypedRecalloc in function ResizeKeyGroup.  For specifications in
xkb_compatibility (compat.c), it is done by an explicit loop in function
InitCompatInfo.

> So really, the only danger we have here is potentially breaking clients that
> expect XkbModAction to be 6 bytes, because of whatever reason. The safest
> approach would be to add a new struct here (XkbModAction2) and use that
> everywhere to avoid this issue. Daniel, any opinion?

Good point, I never thought about this.  I did a quick check in the X
code that comes with NetBSD and it did not turn up any problem, but that
does not mean much, of course.

I would have thought even less about the stuff that Daniel brought up.
I am quite impressed that such a simple change can be so difficult if it
is done right.

Regards,

Andreas