From 0e736276e6421162da0070e98d17d25b9a679de0 Mon Sep 17 00:00:00 2001
From: Andrea Fioraldi <andreafioraldi@gmail.com>
Date: Thu, 4 Mar 2021 11:00:54 +0100
Subject: [PATCH] restore correct CTX behaviour in llvm mode

---
 instrumentation/afl-llvm-pass.so.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/instrumentation/afl-llvm-pass.so.cc b/instrumentation/afl-llvm-pass.so.cc
index 16fd9c94..87267e35 100644
--- a/instrumentation/afl-llvm-pass.so.cc
+++ b/instrumentation/afl-llvm-pass.so.cc
@@ -354,7 +354,8 @@ bool AFLCoverage::runOnModule(Module &M) {
         // if yes we store a context ID for this function in the global var
         if (has_calls) {
 
-          ConstantInt *NewCtx = ConstantInt::get(Int32Ty, AFL_R(map_size));
+          Value *NewCtx = IRB.CreateXor(
+              PrevCtx, ConstantInt::get(Int32Ty, AFL_R(map_size)));
           StoreInst *  StoreCtx = IRB.CreateStore(NewCtx, AFLContext);
           StoreCtx->setMetadata(M.getMDKindID("nosanitize"),
                                 MDNode::get(C, None));