allow get_dr_mcontext() to be called from dr_init() and from event callbacks

[derekbruening]

From [email protected] on April 10, 2009 17:59:46

some clients want the initial app context at init time.
I seem to recall discussing where to allow clients to call
get_dr_mcontext() and we ended up only allowing at clean calls (and now at
syscall events) but not sure now why.

Original issue: http://code.google.com/p/dynamorio/issues/detail?id=117

[derekbruening]

From [email protected] on April 14, 2009 13:41:13

in r140 :

• I wanted to allow it at dr_init() and thread init events but we don't
  have the mcontext available then: the bootstrap code calls init and
  afterward sets up the mconext. so for now only adding bb and trace
  events as valid call sites.

Status: Verified

[derekbruening]

From [email protected] on April 14, 2009 14:03:50

(reviewed by Bharath)

[derekbruening]

From [email protected] on July 02, 2010 08:24:02

in r368 I augmented the feature:
allow get_dr_mcontext() to be called from thread init event, but
only for non-primary threads (would require re-factoring the start/stop API
to provide mcontext at process or primary thread init)

[derekbruening]

From [email protected] on April 26, 2013 09:01:45

issue #1152 covers providing mcontext at primary thread init