Fix handling of errno if external functions are invoked

If an external function in KLEE is invoked, it might update errno.
Previously, the errno specific variable in a state was only updated
if it was part of the executed instructions.
That opened up a timeframe that increased the likelihood of errno being
overwritten by another method call.

This patch fixes two issues:
* the errno of the KLEE process state is updated before the external
function call allowing to detect changes to it later on
* after the external call, the memory object of errno is directly
updated
with its new value, reducing the likelihood to be overwritten by
another
call

Additional features:
* Add support for `errno()` for Darwin as well.
* Simplified errno handling in POSIX layer

1 files changed, 2 insertions, 0 deletions

diff --git a/tools/klee/main.cpp b/tools/klee/main.cpp
index ec951609..44bc5407 100644
--- a/tools/klee/main.cpp
+++ b/tools/klee/main.cpp
@@ -698,6 +698,8 @@ static const char *modelledExternals[] = {
   "_assert",
   "__assert_fail",
   "__assert_rtn",
+  "__errno_location",
+  "__error",
   "calloc",
   "_exit",
   "exit",