K 10
svn:author
V 6
andrew
K 8
svn:date
V 27
2019-10-30T14:05:50.402772Z
K 7
svn:log
V 390
Allow exceptions to be masked when in userspace

We may want to mask exceptions when in userspace. This was previously
impossible as threads are created with all exceptions unmasked and
signals expected userspace to mask any. Fix these by copying the
mask state on thread creation and allow exceptions to be masked on
signal return, as long as they don't change.

Sponsored by:	DARPA, AFRL

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