check leaks at pre-exec, or at exit if exec failed?

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on September 14, 2011 13:20:27_

xref https://bugs.kde.org/show_bug.cgi?id=282018 xref issue #592 Timur: if exec happens then Valgrind doesn't perform the heap scan of the pre-exec memory

today neither drmem nor memcheck does a leak scan prior to an exec. for
most users of exec, they just did a fork, so it makes sense: but I could
have an app that does a bunch of stuff, then does an exec, and maybe the
code prior to the exec is also used as a library somewhere else, so I want
to know about leaks in it. you could also imagine an app that continues on
after a failed exec and does some other stuff. rare though, and perhaps
rare cases should use annotations (I will add a skip-exit-leak-scan annotation to the list in issue #573 ) while the default should focus on the
common case.

though w/o marking other thread stacks as unaddr ( issue #592 ), the only risk of doing the scan is from pointers that were in thread registers.

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=593_