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, 3 insertions, 0 deletions

diff --git a/include/klee/klee.h b/include/klee/klee.h
index 644c498e..8b9cd2e2 100644
--- a/include/klee/klee.h
+++ b/include/klee/klee.h
@@ -157,6 +157,9 @@ extern "C" {
 
   /* Merge all paths of the state that went through klee_open_merge */
   void klee_close_merge();
+
+  /* Get errno value of the current state */
+  int klee_get_errno(void);
 #ifdef __cplusplus
 }
 #endif