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/lib/Core/ExternalDispatcher.h b/lib/Core/ExternalDispatcher.h
index c64dc7d8..7c3a1d79 100644
--- a/lib/Core/ExternalDispatcher.h
+++ b/lib/Core/ExternalDispatcher.h
@@ -40,6 +40,9 @@ public:
   bool executeCall(llvm::Function *function, llvm::Instruction *i,
                    uint64_t *args);
   void *resolveSymbol(const std::string &name);
+
+  int getLastErrno();
+  void setLastErrno(int newErrno);
 };
 }