Dev (#949)

* use atomic read-modify-write increment for LLVM CLASSIC

* Change other LLVM modes to atomic increments

* sync (#886)

* Create FUNDING.yml

* Update FUNDING.yml

* moved custom_mutator examples

* unicorn speedtest makefile cleanup

* fixed example location

* fix qdbi

* update util readme

* work in progress: not working correctly yet

* Frida persistent (#880)

* Added x64 support for persistent mode (function call only), in-memory teest cases and complog

* Review changes, fix NeverZero and code to parse the .text section of the main executable. Excluded ranges TBC

* Various minor fixes and finished support for AFL_INST_LIBS

* Review changes

Co-authored-by: Your Name <you@example.com>

* nits

* fix frida mode

* Integer overflow/underflow fixes in libdislocator (#889)

* libdislocator: fixing integer overflow in 'max_mem' variable and setting 'max_mem' type to 'size_t'

* libdislocator: fixing potential integer underflow in 'total_mem' variable due to its different values in different threads

* Bumped warnings up to the max and fixed remaining issues (#890)

Co-authored-by: Your Name <you@example.com>

* nits

* frida mode - support non-pie

* nits

* nit

* update grammar mutator

* Fixes for aarch64, OSX and other minor issues (#891)

Co-authored-by: Your Name <you@example.com>

* nits

* nits

* fix PCGUARD, build aflpp_driver with fPIC

* Added representative fuzzbench test and test for libxml (#893)

* Added representative fuzzbench test and test for libxml

* Added support for building FRIDA from source with FRIDA_SOURCE=1

Co-authored-by: Your Name <you@example.com>

* nits

* update changelog

* typos

* still not working

* fixed potential double free in custom trim (#881)

* error handling, freeing mem

* frida: complog -> cmplog

* fix statsd writing

* let aflpp_qemu_driver_hook.so build fail gracefully

* fix stdin trimming

* Support for AFL_ENTRYPOINT (#898)

Co-authored-by: Your Name <you@example.com>

* remove the input file .cur_input at the end of the fuzzing, if AFL_TMPDIR is used

* reverse push (#901)

* Create FUNDING.yml

* Update FUNDING.yml

* disable QEMU static pie

Co-authored-by: Andrea Fioraldi <andreafioraldi@gmail.com>

* clarify that no modifications are required.

* add new test for frida_mode (please review)

* typos

* fix persistent mode (64-bit)

* set ARCH for linux intel 32-bit for frida-gum-devkit

* prepare for 32-bit support (later)

* not on qemu 3 anymore

* unicorn mips fixes

* instrumentation further move to C++11 (#900)

* unicorn fixes

* first working NeverZero implementation

* more unicorn fixes

* Fix memory errors when trim causes testcase growth (#881) (#903)

* Revert "fixed potential double free in custom trim (#881)"

This reverts commit e9d2f72382cab75832721d859c3e731da071435d.

* Revert "fix custom trim for increasing data"

This reverts commit 86a8ef168dda766d2f25f15c15c4d3ecf21d0667.

* Fix memory errors when trim causes testcase growth

Modify trim_case_custom to avoid writing into in_buf because
some custom mutators can cause the testcase to grow rather than
shrink.

Instead of modifying in_buf directly, we write the update out
to the disk when trimming is complete, and then the caller is
responsible for refreshing the in-memory buffer from the file.

This is still a bit sketchy because it does need to modify q->len in
order to notify the upper layers that something changed, and it could
end up telling upper layer code that the q->len is *bigger* than
the buffer (q->testcase_buf) that contains it, which is asking
for trouble down the line somewhere...

* Fix an unlikely situation

Put back some `unlikely()` calls that were in
the e9d2f72382cab75832721d859c3e731da071435d commit that was
reverted.

* add some comments

* typo

* Exit on time (#904)

* Variable AFL_EXIT_ON_TIME description has been added.
Variables AFL_EXIT_ON_TIME and afl_exit_on_time has been added.
afl->exit_on_time variable initialization has been added.
The asignment of a value to the afl->afl_env.afl_exit_on_time variable from
environment variables has been added.
Code to exit on timeout if new path not found has been added.

* Type of afl_exit_on_time variable has been changed.
Variable exit_on_time has been added to the afl_state_t structure.

* Command `export AFL_EXIT_WHEN_DONE=1` has been added.

* Millisecond to second conversion has been added.
Call get_cur_time() has been added.

* Revert to using the saved current time value.

* Useless check has been removed.

* fix new path to custom-mutators

* ensure crashes/README.txt exists

* fix

* Changes to bump FRIDA version and to clone FRIDA repo in to build directory rather than use a submodule as the FRIDA build scripts don't like it (#906)

Co-authored-by: Your Name <you@example.com>

* Fix numeric overflow in cmplog implementation (#907)

Co-authored-by: Your Name <you@example.com>

* testcase fixes for unicorn

* remove merge conflict artifacts

* fix afl-plot

* Changes to remove binaries from frida_mode (#913)

Co-authored-by: Your Name <you@example.com>

* Frida cmplog fail fast (#914)

* Changes to remove binaries from frida_mode

* Changes to make cmplog fail fast

Co-authored-by: Your Name <you@example.com>

* afl-plot: relative time

* arch linux and mac os support for afl-system-config

* typo

* code-format

* update documentation

* github workflow for qemu

* OSX-specific improvements (#912)

* Fix afl-cc to work correctly by default on OSX using xcode

- CLANG_ENV_VAR must be set for afl-as to work
- Use clang mode by default if no specific compiler selected

* Add OSX-specific documentation for configuring shared memory

* Fixes to memory operands for complog (#916)

Co-authored-by: Your Name <you@example.com>

* fix a few cur_time uses

* added bounds check to pivot_inputs (fixes #921)

* additional safety checks for restarts

* restrict afl-showmap in_file size

* fix seed crash disable

* add warning for afl-showmap partial read

* no core dumps

* AFL_PRINT_FILENAMES added

* more documentation for AFL_EXIT_ON_TIME

* Flushing for AFL_PRINT_FILENAMES

* FASAN Support (#918)

* FASAN Support

* Fix handling of Address Sanitizer DSO

* Changes to identification of Address Sanitizer DSO

Co-authored-by: Your Name <you@example.com>

* Support for x86 (#920)

Co-authored-by: Your Name <you@example.com>

* Update frida_mode readme (#925)

* libqasan: use syscalls for read and write

* update readme

* Minor integration tweaks (#926)

Co-authored-by: Your Name <you@example.com>

* merge

* fix afl-fuzz.c frida preload

* cleaned up AFL_PRINT_FILENAMES env

* Changes to have persistent mode exit at the end of the loop (#928)

Co-authored-by: Your Name <you@example.com>

* fix llvm-dict2file

* push to stable (#931) (#932)

* sync (#886)

* Create FUNDING.yml

* Update FUNDING.yml

* moved custom_mutator examples

* unicorn speedtest makefile cleanup

* fixed example location

* fix qdbi

* update util readme

* Frida persistent (#880)

* Added x64 support for persistent mode (function call only), in-memory teest cases and complog

* Review changes, fix NeverZero and code to parse the .text section of the main executable. Excluded ranges TBC

* Various minor fixes and finished support for AFL_INST_LIBS

* Review changes

Co-authored-by: Your Name <you@example.com>

* nits

* fix frida mode

* Integer overflow/underflow fixes in libdislocator (#889)

* libdislocator: fixing integer overflow in 'max_mem' variable and setting 'max_mem' type to 'size_t'

* libdislocator: fixing potential integer underflow in 'total_mem' variable due to its different values in different threads

* Bumped warnings up to the max and fixed remaining issues (#890)

Co-authored-by: Your Name <you@example.com>

* nits

* frida mode - support non-pie

* nits

* nit

* update grammar mutator

* Fixes for aarch64, OSX and other minor issues (#891)

Co-authored-by: Your Name <you@example.com>

* nits

* nits

* fix PCGUARD, build aflpp_driver with fPIC

* Added representative fuzzbench test and test for libxml (#893)

* Added representative fuzzbench test and test for libxml

* Added support for building FRIDA from source with FRIDA_SOURCE=1

Co-authored-by: Your Name <you@example.com>

* nits

* update changelog

* typos

* fixed potential double free in custom trim (#881)

* error handling, freeing mem

* frida: complog -> cmplog

* fix statsd writing

* let aflpp_qemu_driver_hook.so build fail gracefully

* fix stdin trimming

* Support for AFL_ENTRYPOINT (#898)

Co-authored-by: Your Name <you@example.com>

* remove the input file .cur_input at the end of the fuzzing, if AFL_TMPDIR is used

* reverse push (#901)

* Create FUNDING.yml

* Update FUNDING.yml

* disable QEMU static pie

Co-authored-by: Andrea Fioraldi <andreafioraldi@gmail.com>

* clarify that no modifications are required.

* add new test for frida_mode (please review)

* typos

* fix persistent mode (64-bit)

* set ARCH for linux intel 32-bit for frida-gum-devkit

* prepare for 32-bit support (later)

* not on qemu 3 anymore

* unicorn mips fixes

* instrumentation further move to C++11 (#900)

* unicorn fixes

* more unicorn fixes

* Fix memory errors when trim causes testcase growth (#881) (#903)

* Revert "fixed potential double free in custom trim (#881)"

This reverts commit e9d2f72382cab75832721d859c3e731da071435d.

* Revert "fix custom trim for increasing data"

This reverts commit 86a8ef168dda766d2f25f15c15c4d3ecf21d0667.

* Fix memory errors when trim causes testcase growth

Modify trim_case_custom to avoid writing into in_buf because
some custom mutators can cause the testcase to grow rather than
shrink.

Instead of modifying in_buf directly, we write the update out
to the disk when trimming is complete, and then the caller is
responsible for refreshing the in-memory buffer from the file.

This is still a bit sketchy because it does need to modify q->len in
order to notify the upper layers that something changed, and it could
end up telling upper layer code that the q->len is *bigger* than
the buffer (q->testcase_buf) that contains it, which is asking
for trouble down the line somewhere...

* Fix an unlikely situation

Put back some `unlikely()` calls that were in
the e9d2f72382cab75832721d859c3e731da071435d commit that was
reverted.

* typo

* Exit on time (#904)

* Variable AFL_EXIT_ON_TIME description has been added.
Variables AFL_EXIT_ON_TIME and afl_exit_on_time has been added.
afl->exit_on_time variable initialization has been added.
The asignment of a value to the afl->afl_env.afl_exit_on_time variable from
environment variables has been added.
Code to exit on timeout if new path not found has been added.

* Type of afl_exit_on_time variable has been changed.
Variable exit_on_time has been added to the afl_state_t structure.

* Command `export AFL_EXIT_WHEN_DONE=1` has been added.

* Millisecond to second conversion has been added.
Call get_cur_time() has been added.

* Revert to using the saved current time value.

* Useless check has been removed.

* fix new path to custom-mutators

* ensure crashes/README.txt exists

* fix

* Changes to bump FRIDA version and to clone FRIDA repo in to build directory rather than use a submodule as the FRIDA build scripts don't like it (#906)

Co-authored-by: Your Name <you@example.com>

* Fix numeric overflow in cmplog implementation (#907)

Co-authored-by: Your Name <you@example.com>

* testcase fixes for unicorn

* remove merge conflict artifacts

* fix afl-plot

* Changes to remove binaries from frida_mode (#913)

Co-authored-by: Your Name <you@example.com>

* Frida cmplog fail fast (#914)

* Changes to remove binaries from frida_mode

* Changes to make cmplog fail fast

Co-authored-by: Your Name <you@example.com>

* afl-plot: relative time

* arch linux and mac os support for afl-system-config

* typo

* code-format

* update documentation

* github workflow for qemu

* OSX-specific improvements (#912)

* Fix afl-cc to work correctly by default on OSX using xcode

- CLANG_ENV_VAR must be set for afl-as to work
- Use clang mode by default if no specific compiler selected

* Add OSX-specific documentation for configuring shared memory

* Fixes to memory operands for complog (#916)

Co-authored-by: Your Name <you@example.com>

* fix a few cur_time uses

* added bounds check to pivot_inputs (fixes #921)

* additional safety checks for restarts

* restrict afl-showmap in_file size

* fix seed crash disable

* add warning for afl-showmap partial read

* no core dumps

* AFL_PRINT_FILENAMES added

* more documentation for AFL_EXIT_ON_TIME

* Flushing for AFL_PRINT_FILENAMES

* FASAN Support (#918)

* FASAN Support

* Fix handling of Address Sanitizer DSO

* Changes to identification of Address Sanitizer DSO

Co-authored-by: Your Name <you@example.com>

* Support for x86 (#920)

Co-authored-by: Your Name <you@example.com>

* Update frida_mode readme (#925)

* libqasan: use syscalls for read and write

* update readme

* Minor integration tweaks (#926)

Co-authored-by: Your Name <you@example.com>

* merge

* fix afl-fuzz.c frida preload

* cleaned up AFL_PRINT_FILENAMES env

* Changes to have persistent mode exit at the end of the loop (#928)

Co-authored-by: Your Name <you@example.com>

* fix llvm-dict2file

Co-authored-by: Dominik Maier <domenukk@gmail.com>
Co-authored-by: WorksButNotTested <62701594+WorksButNotTested@users.noreply.github.com>
Co-authored-by: Your Name <you@example.com>
Co-authored-by: Dmitry Zheregelya <zheregelya.d@gmail.com>
Co-authored-by: hexcoder <hexcoder-@users.noreply.github.com>
Co-authored-by: hexcoder- <heiko@hexco.de>
Co-authored-by: Andrea Fioraldi <andreafioraldi@gmail.com>
Co-authored-by: David CARLIER <devnexen@gmail.com>
Co-authored-by: realmadsci <71108352+realmadsci@users.noreply.github.com>
Co-authored-by: Roman M. Iudichev <SecNotice@ya.ru>
Co-authored-by: Dustin Spicuzza <dustin@virtualroadside.com>

Co-authored-by: Dominik Maier <domenukk@gmail.com>
Co-authored-by: WorksButNotTested <62701594+WorksButNotTested@users.noreply.github.com>
Co-authored-by: Your Name <you@example.com>
Co-authored-by: Dmitry Zheregelya <zheregelya.d@gmail.com>
Co-authored-by: hexcoder <hexcoder-@users.noreply.github.com>
Co-authored-by: hexcoder- <heiko@hexco.de>
Co-authored-by: Andrea Fioraldi <andreafioraldi@gmail.com>
Co-authored-by: David CARLIER <devnexen@gmail.com>
Co-authored-by: realmadsci <71108352+realmadsci@users.noreply.github.com>
Co-authored-by: Roman M. Iudichev <SecNotice@ya.ru>
Co-authored-by: Dustin Spicuzza <dustin@virtualroadside.com>

* improve error msg

* Added documentation for wine LoadLibrary workaround (#933)

* Fix cmake target compilation command example (#934)

- Fix typo DCMAKE_C_COMPILERC -> DCMAKE_C_COMPILER.
- Add `cd build` after `mkdir build`.

* showmap passes queue items in alphabetical order

* added tmp files to gitignore

* lenient dict parsing, no map size enum for binary fuzzing

* added info about showmap queue directions

* update binary-only doc

* turn off map size detection if skip_bin_check is set

* Typo

* update docs

* update afl-system-config

* Set kill signal before using it in afl-showmap (#935)

* fix afl-cc help output

* add libafl to binary-only doc

* update docs

* less executions on variable paths

* AFL_SKIP_CRASHES is obsolete since 3.0

* add AFL_TRY_AFFINITY

* Typo

* Typo

* Typo/wording

* tweaks

* typos

* fix afl-whatsup help output

* fix afl-plot output

* fix for MacOS

* fix cmpcov doc for qemu

* fix tmpfile removal

* update dockerfile

* Frida (#940)

* Added re2 test

* Added libpcap test

* Fix validation of setting of ADDR_NO_RANDOMIZE

* Added support for printing original and instrumented code

Co-authored-by: Your Name <you@example.com>

* Support for AFL_FRIDA_PERSISTENT_RET (#941)

Co-authored-by: Your Name <you@example.com>

* Changes to add missing exclusion of ranges (#943)

Co-authored-by: Your Name <you@example.com>

* add --afl-noopt to afl-cc

* docs: fix link to README in QuickStartGuide (#946)

* Support writing Stalker stats (#945)

* Support writing Stalker stats

* Fixed string handling in print functions

Co-authored-by: Your Name <you@example.com>

* afl-cmin help fix, aflpp_driver - + @@ support

* fix for afl-showmap

* support new env var AFL_LLVM_THREADSAFE_INST to enable atomic counters.
add new test case for that.

* add documentation for AFL_LLVM_THREADSAFE_INST

* add support for AFL_LLVM_THREADSAFE_INST to other LLVM passes

* add missing include for _exit()

* threadsafe doc fixes, code format

* Wording: "never zero" -> NeverZero

* fix afl_custom_post_process with multiple custom mutators

* fix docs

* debug ck_write

* fixed potential diff by 0

* fixes

* fix classic threadsafe counters

Co-authored-by: van Hauser <vh@thc.org>
Co-authored-by: Dominik Maier <domenukk@gmail.com>
Co-authored-by: WorksButNotTested <62701594+WorksButNotTested@users.noreply.github.com>
Co-authored-by: Your Name <you@example.com>
Co-authored-by: Dmitry Zheregelya <zheregelya.d@gmail.com>
Co-authored-by: Andrea Fioraldi <andreafioraldi@gmail.com>
Co-authored-by: David CARLIER <devnexen@gmail.com>
Co-authored-by: realmadsci <71108352+realmadsci@users.noreply.github.com>
Co-authored-by: Roman M. Iudichev <SecNotice@ya.ru>
Co-authored-by: Dustin Spicuzza <dustin@virtualroadside.com>
Co-authored-by: 0x4d5a-ctf <51098072+0x4d5a-ctf@users.noreply.github.com>
Co-authored-by: Tommy Chiang <oToToT@users.noreply.github.com>
Co-authored-by: buherator <buherator@silentsignal.hu>
Co-authored-by: Dag Heyman Kajevic <dag.heyman@gmail.com>

1 files changed, 206 insertions, 28 deletions

diff --git a/instrumentation/afl-llvm-pass.so.cc b/instrumentation/afl-llvm-pass.so.cc
index 0f773aba..a8f1baff 100644
--- a/instrumentation/afl-llvm-pass.so.cc
+++ b/instrumentation/afl-llvm-pass.so.cc
@@ -81,11 +81,12 @@ class AFLCoverage : public ModulePass {
   bool runOnModule(Module &M) override;
 
  protected:
-  uint32_t ngram_size = 0;
-  uint32_t ctx_k = 0;
-  uint32_t map_size = MAP_SIZE;
-  uint32_t function_minimum_size = 1;
-  char *   ctx_str = NULL, *caller_str = NULL, *skip_nozero = NULL;
+  uint32_t    ngram_size = 0;
+  uint32_t    ctx_k = 0;
+  uint32_t    map_size = MAP_SIZE;
+  uint32_t    function_minimum_size = 1;
+  const char *ctx_str = NULL, *caller_str = NULL, *skip_nozero = NULL;
+  const char *use_threadsafe_counters = nullptr;
 
 };
 
@@ -182,6 +183,38 @@ bool AFLCoverage::runOnModule(Module &M) {
   char *neverZero_counters_str = getenv("AFL_LLVM_NOT_ZERO");
 #endif
   skip_nozero = getenv("AFL_LLVM_SKIP_NEVERZERO");
+  use_threadsafe_counters = getenv("AFL_LLVM_THREADSAFE_INST");
+
+  if ((isatty(2) && !getenv("AFL_QUIET")) || !!getenv("AFL_DEBUG")) {
+
+    if (use_threadsafe_counters) {
+
+      // disabled unless there is support for other modules as well
+      // (increases documentation complexity)
+      /*      if (!getenv("AFL_LLVM_NOT_ZERO")) { */
+
+      skip_nozero = "1";
+      SAYF(cCYA "afl-llvm-pass" VERSION cRST " using thread safe counters\n");
+
+      /*
+
+            } else {
+
+              SAYF(cCYA "afl-llvm-pass" VERSION cRST
+                        " using thread safe not-zero-counters\n");
+
+            }
+
+      */
+
+    } else {
+
+      SAYF(cCYA "afl-llvm-pass" VERSION cRST
+                " using non-thread safe instrumentation\n");
+
+    }
+
+  }
 
   unsigned PrevLocSize = 0;
   unsigned PrevCallerSize = 0;
@@ -388,7 +421,6 @@ bool AFLCoverage::runOnModule(Module &M) {
 #endif
 
   // other constants we need
-  ConstantInt *Zero = ConstantInt::get(Int8Ty, 0);
   ConstantInt *One = ConstantInt::get(Int8Ty, 1);
 
   Value *   PrevCtx = NULL;     // CTX sensitive coverage
@@ -410,6 +442,7 @@ bool AFLCoverage::runOnModule(Module &M) {
 
     if (F.size() < function_minimum_size) continue;
 
+    std::list<Value *> todo;
     for (auto &BB : F) {
 
       BasicBlock::iterator IP = BB.getFirstInsertionPt();
@@ -628,37 +661,68 @@ bool AFLCoverage::runOnModule(Module &M) {
 
       /* Update bitmap */
 
-      LoadInst *Counter = IRB.CreateLoad(MapPtrIdx);
-      Counter->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None));
+      if (use_threadsafe_counters) {                              /* Atomic */
+                                     /*
+                                     #if LLVM_VERSION_MAJOR < 9
+                                             if (neverZero_counters_str !=
+                                                 NULL) {  // with llvm 9 we make this the default as the bug
+                                     in llvm
+                                                          // is then fixed
+                                     #else
+                                             if (!skip_nozero) {
+                             
+                                     #endif
+                                               // register MapPtrIdx in a todo list
+                                               todo.push_back(MapPtrIdx);
+                             
+                                             } else {
+
+                                     */
+        IRB.CreateAtomicRMW(llvm::AtomicRMWInst::BinOp::Add, MapPtrIdx, One,
+                            llvm::AtomicOrdering::Monotonic);
+        /*
+
+                }
+
+        */
 
-      Value *Incr = IRB.CreateAdd(Counter, One);
+      } else {
+
+        LoadInst *Counter = IRB.CreateLoad(MapPtrIdx);
+        Counter->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None));
+
+        Value *Incr = IRB.CreateAdd(Counter, One);
 
 #if LLVM_VERSION_MAJOR < 9
-      if (neverZero_counters_str !=
-          NULL) {  // with llvm 9 we make this the default as the bug in llvm is
-                   // then fixed
+        if (neverZero_counters_str !=
+            NULL) {  // with llvm 9 we make this the default as the bug in llvm
+                     // is then fixed
 #else
-      if (!skip_nozero) {
+        if (!skip_nozero) {
 
 #endif
-        /* hexcoder: Realize a counter that skips zero during overflow.
-         * Once this counter reaches its maximum value, it next increments to 1
-         *
-         * Instead of
-         * Counter + 1 -> Counter
-         * we inject now this
-         * Counter + 1 -> {Counter, OverflowFlag}
-         * Counter + OverflowFlag -> Counter
-         */
+          /* hexcoder: Realize a counter that skips zero during overflow.
+           * Once this counter reaches its maximum value, it next increments to
+           * 1
+           *
+           * Instead of
+           * Counter + 1 -> Counter
+           * we inject now this
+           * Counter + 1 -> {Counter, OverflowFlag}
+           * Counter + OverflowFlag -> Counter
+           */
+
+          ConstantInt *Zero = ConstantInt::get(Int8Ty, 0);
+          auto         cf = IRB.CreateICmpEQ(Incr, Zero);
+          auto         carry = IRB.CreateZExt(cf, Int8Ty);
+          Incr = IRB.CreateAdd(Incr, carry);
 
-        auto cf = IRB.CreateICmpEQ(Incr, Zero);
-        auto carry = IRB.CreateZExt(cf, Int8Ty);
-        Incr = IRB.CreateAdd(Incr, carry);
+        }
 
-      }
+        IRB.CreateStore(Incr, MapPtrIdx)
+            ->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None));
 
-      IRB.CreateStore(Incr, MapPtrIdx)
-          ->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None));
+      }                                                  /* non atomic case */
 
       /* Update prev_loc history vector (by placing cur_loc at the head of the
          vector and shuffle the other elements back by one) */
@@ -715,6 +779,120 @@ bool AFLCoverage::runOnModule(Module &M) {
 
     }
 
+#if 0
+    if (use_threadsafe_counters) {                       /*Atomic NeverZero */
+      // handle the list of registered blocks to instrument
+      for (auto val : todo) {
+
+        /* hexcoder: Realize a thread-safe counter that skips zero during
+         * overflow. Once this counter reaches its maximum value, it next
+         * increments to 1
+         *
+         * Instead of
+         * Counter + 1 -> Counter
+         * we inject now this
+         * Counter + 1 -> {Counter, OverflowFlag}
+         * Counter + OverflowFlag -> Counter
+         */
+
+        /* equivalent c code looks like this
+         * Thanks to
+         https://preshing.com/20150402/you-can-do-any-kind-of-atomic-read-modify-write-operation/
+
+            int old = atomic_load_explicit(&Counter, memory_order_relaxed);
+            int new;
+            do {
+
+                 if (old == 255) {
+
+                   new = 1;
+
+                 } else {
+
+                   new = old + 1;
+
+                 }
+
+            } while (!atomic_compare_exchange_weak_explicit(&Counter, &old, new,
+
+         memory_order_relaxed, memory_order_relaxed));
+
+         */
+
+        Value *              MapPtrIdx = val;
+        Instruction *        MapPtrIdxInst = cast<Instruction>(val);
+        BasicBlock::iterator it0(&(*MapPtrIdxInst));
+        ++it0;
+        IRBuilder<> IRB(&(*it0));
+
+        // load the old counter value atomically
+        LoadInst *Counter = IRB.CreateLoad(MapPtrIdx);
+        Counter->setAlignment(llvm::Align());
+        Counter->setAtomic(llvm::AtomicOrdering::Monotonic);
+        Counter->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None));
+
+        BasicBlock *BB = IRB.GetInsertBlock();
+        // insert a basic block with the corpus of a do while loop
+        // the calculation may need to repeat, if atomic compare_exchange is not
+        // successful
+
+        BasicBlock::iterator it(*Counter);
+        it++;  // split after load counter
+        BasicBlock *end_bb = BB->splitBasicBlock(it);
+        end_bb->setName("injected");
+
+        // insert the block before the second half of the split
+        BasicBlock *do_while_bb =
+            BasicBlock::Create(C, "injected", end_bb->getParent(), end_bb);
+
+        // set terminator of BB from target end_bb to target do_while_bb
+        auto term = BB->getTerminator();
+        BranchInst::Create(do_while_bb, BB);
+        term->eraseFromParent();
+
+        // continue to fill instructions into the do_while loop
+        IRB.SetInsertPoint(do_while_bb, do_while_bb->getFirstInsertionPt());
+
+        PHINode *PN = IRB.CreatePHI(Int8Ty, 2);
+
+        // compare with maximum value 0xff
+        auto *Cmp = IRB.CreateICmpEQ(Counter, ConstantInt::get(Int8Ty, -1));
+
+        // increment the counter
+        Value *Incr = IRB.CreateAdd(Counter, One);
+
+        // select the counter value or 1
+        auto *Select = IRB.CreateSelect(Cmp, One, Incr);
+
+        // try to save back the new counter value
+        auto *CmpXchg = IRB.CreateAtomicCmpXchg(
+            MapPtrIdx, PN, Select, llvm::AtomicOrdering::Monotonic,
+            llvm::AtomicOrdering::Monotonic);
+        CmpXchg->setAlignment(llvm::Align());
+        CmpXchg->setWeak(true);
+        CmpXchg->setMetadata(M.getMDKindID("nosanitize"), MDNode::get(C, None));
+
+        // get the result of trying to update the Counter
+        Value *Success =
+            IRB.CreateExtractValue(CmpXchg, ArrayRef<unsigned>({1}));
+        // get the (possibly updated) value of Counter
+        Value *OldVal =
+            IRB.CreateExtractValue(CmpXchg, ArrayRef<unsigned>({0}));
+
+        // initially we use Counter
+        PN->addIncoming(Counter, BB);
+        // on retry, we use the updated value
+        PN->addIncoming(OldVal, do_while_bb);
+
+        // if the cmpXchg was not successful, retry
+        IRB.CreateCondBr(Success, end_bb, do_while_bb);
+
+      }
+
+    }
+
+#endif
+
   }
 
   /*