[dfsan] Add "DataFlow" option to LLVM_USE_SANITIZER

Summary:
This patch add the dataflow option to LLVM_USE_SANITIZER and documents
it.

Tested via check-cxx (wip to fix the errors).

Reviewers: morehouse, #libc!

Subscribers: mgorny, cfe-commits, libcxx-commits

Tags: #clang, #libc

Differential Revision: https://reviews.llvm.org/D78390

Author: Zola Bridges

clang/docs/DataFlowSanitizer.rst

@@ -20,6 +20,31 @@ specific class of bugs on its own.  Instead, it provides a generic
 dynamic data flow analysis framework to be used by clients to help
 detect application-specific issues within their own code.
 
+How to build libc++ with DFSan
+==============================
+
+DFSan requires either all of your code to be instrumented or for uninstrumented
+functions to be listed as``uninstrumented`` in the `ABI list`_.
+
+If you'd like to have instrumented libc++ functions, then you need to build it
+with DFSan instrumentation from source. Here is an example of how to build
+libc++ and the libc++ ABI with data flow sanitizer instrumentation.
+
+.. code-block:: console
+  cd libcxx-build
+
+  # An example using ninja
+  cmake -GNinja path/to/llvm-project/llvm \
+    -DCMAKE_C_COMPILER=clang \
+    -DCMAKE_CXX_COMPILER=clang++ \
+    -DLLVM_USE_SANITIZER="DataFlow" \
+    -DLLVM_ENABLE_LIBCXX=ON \
+    -DLLVM_ENABLE_PROJECTS="libcxx;libcxxabi"
+
+  ninja cxx cxxabi
+
+Note: Ensure you are building with a sufficiently new version of Clang.
+
 Usage
 =====
 
@@ -33,6 +58,8 @@ The APIs are defined in the header file ``sanitizer/dfsan_interface.h``.
 For further information about each function, please refer to the header
 file.
 
+.. _ABI list:
+
 ABI List
 --------
 

libcxx/CMakeLists.txt

@@ -682,6 +682,8 @@ function(get_sanitizer_flags OUT_VAR  USE_SANITIZER)
       append_flags(SANITIZER_FLAGS "-fsanitize=address,undefined -fno-sanitize=vptr,function -fno-sanitize-recover=all")
     elseif (USE_SANITIZER STREQUAL "Thread")
       append_flags(SANITIZER_FLAGS -fsanitize=thread)
+    elseif (USE_SANITIZER STREQUAL "DataFlow")
+      append_flags(SANITIZER_FLAGS -fsanitize=dataflow)
     else()
       message(WARNING "Unsupported value of LLVM_USE_SANITIZER: ${USE_SANITIZER}")
     endif()

libcxx/utils/libcxx/test/config.py

@@ -907,6 +907,8 @@ def add_ubsan():
                 self.cxx.flags += ['-fsanitize=thread']
                 self.config.available_features.add('tsan')
                 self.config.available_features.add('sanitizer-new-delete')
+            elif san == 'DataFlow':
+                self.cxx.flags += ['-fsanitize=dataflow']
             else:
                 self.lit_config.fatal('unsupported value for '
                                       'use_sanitizer: {0}'.format(san))

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -728,6 +728,8 @@ if(LLVM_USE_SANITIZER)
     elseif (LLVM_USE_SANITIZER STREQUAL "Thread")
       append_common_sanitizer_flags()
       append("-fsanitize=thread" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+    elseif (LLVM_USE_SANITIZER STREQUAL "DataFlow")
+      append("-fsanitize=dataflow" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
     elseif (LLVM_USE_SANITIZER STREQUAL "Address;Undefined" OR
             LLVM_USE_SANITIZER STREQUAL "Undefined;Address")
       append_common_sanitizer_flags()

llvm/docs/CMake.rst

@@ -422,7 +422,7 @@ LLVM-specific variables
 **LLVM_USE_SANITIZER**:STRING
   Define the sanitizer used to build LLVM binaries and tests. Possible values
   are ``Address``, ``Memory``, ``MemoryWithOrigins``, ``Undefined``, ``Thread``,
-  and ``Address;Undefined``. Defaults to empty string.
+  ``DataFlow``, and ``Address;Undefined``. Defaults to empty string.
 
 **LLVM_ENABLE_LTO**:STRING
   Add ``-flto`` or ``-flto=`` flags to the compile and link command