[libc++] Add build and CI support for pointer field protection

[pcc]

Add support for building the libc++ runtime with pointer field
protection with a new CMake variable, LIBCXX_PFP. Add a new case to
libcxx/utils/ci/run-buildbot named bootstrapping-build-pfp that runs
the libc++ and libc++abi tests.

This implements the LLVM side of the CI support proposed in:
https://discourse.llvm.org/t/rfc-libc-and-pointer-field-protection/87713

[llvmbot]

@llvm/pr-subscribers-libcxxabi

@llvm/pr-subscribers-libcxx

Author: Peter Collingbourne (pcc)

Changes

Add support for building the libc++ runtime with pointer field
protection with a new CMake variable, LIBCXX_PFP. Add a new case to
libcxx/utils/ci/run-buildbot named bootstrapping-build-pfp that runs
the libc++ and libc++abi tests.

This implements the LLVM side of the CI support proposed in:
https://discourse.llvm.org/t/rfc-libc-and-pointer-field-protection/87713

---

Full diff: https://github.com/llvm/llvm-project/pull/152414.diff

5 Files Affected:

• (modified) libcxx/CMakeLists.txt (+15)
• (modified) libcxx/test/CMakeLists.txt (+1)
• (modified) libcxx/utils/ci/run-buildbot (+36)
• (modified) libcxx/utils/libcxx/test/params.py (+16)
• (modified) libcxxabi/test/CMakeLists.txt (+2)

diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 85514cc7547a9..05f342d7002b3 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -66,6 +66,14 @@ if (NOT "${LIBCXX_HARDENING_MODE}" IN_LIST LIBCXX_SUPPORTED_HARDENING_MODES)
   message(FATAL_ERROR
     "Unsupported hardening mode: '${LIBCXX_HARDENING_MODE}'. Supported values are ${LIBCXX_SUPPORTED_HARDENING_MODES}.")
 endif()
+set(LIBCXX_SUPPORTED_PFP none untagged tagged)
+set(LIBCXX_PFP none CACHE STRING
+  "Specify whether to build with pointer field protection.
+   Supported values are ${LIBCXX_SUPPORTED_PFP}.")
+if (NOT "${LIBCXX_PFP}" IN_LIST LIBCXX_SUPPORTED_PFP)
+  message(FATAL_ERROR
+    "Unsupported PFP mode: '${LIBCXX_PFP}'. Supported values are ${LIBCXX_SUPPORTED_PFP}.")
+endif()
 set(LIBCXX_ASSERTION_HANDLER_FILE
   "vendor/llvm/default_assertion_handler.in"
   CACHE STRING
@@ -564,6 +572,12 @@ function(cxx_add_rtti_flags target)
   endif()
 endfunction()
 
+function(cxx_add_pfp_flags target)
+  if (NOT LIBCXX_PFP STREQUAL none)
+    target_add_compile_flags_if_supported(${target} PUBLIC -fexperimental-pointer-field-protection=${LIBCXX_PFP})
+  endif()
+endfunction()
+
 # Modules flags ===============================================================
 # FIXME The libc++ sources are fundamentally non-modular. They need special
 # versions of the headers in order to provide C++03 and legacy ABI definitions.
@@ -820,6 +834,7 @@ function(cxx_add_common_build_flags target)
   cxx_add_windows_flags(${target})
   cxx_add_exception_flags(${target})
   cxx_add_rtti_flags(${target})
+  cxx_add_pfp_flags(${target})
   cxx_add_module_flags(${target})
   cxx_link_system_libraries(${target})
   target_link_libraries(${target} PRIVATE cxx-sanitizer-flags)
diff --git a/libcxx/test/CMakeLists.txt b/libcxx/test/CMakeLists.txt
index f4e577aed57de..340f3d3c44101 100644
--- a/libcxx/test/CMakeLists.txt
+++ b/libcxx/test/CMakeLists.txt
@@ -79,6 +79,7 @@ if (NOT LIBCXX_ENABLE_RTTI)
 endif()
 
 serialize_lit_string_param(SERIALIZED_LIT_PARAMS hardening_mode "${LIBCXX_HARDENING_MODE}")
+serialize_lit_string_param(SERIALIZED_LIT_PARAMS pfp "${LIBCXX_PFP}")
 
 if (CMAKE_CXX_COMPILER_TARGET)
   serialize_lit_string_param(SERIALIZED_LIT_PARAMS target_triple "${CMAKE_CXX_COMPILER_TARGET}")
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
index 57ecf1e49dbf2..9965ebe78b497 100755
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -411,6 +411,42 @@ bootstrapping-build)
 
     ccache -s
 ;;
+bootstrapping-build-pfp)
+    clean
+
+    triple="$(${CXX} --print-target-triple)"
+
+    step "Generating CMake"
+    ${CMAKE} \
+          -S "${MONOREPO_ROOT}/llvm" \
+          -B "${BUILD_DIR}" \
+          -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
+          -DCMAKE_BUILD_TYPE=Release \
+          -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
+          -DLLVM_ENABLE_PROJECTS="clang;lld" \
+          -DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx;libcxxabi;libunwind" \
+          -DLLVM_RUNTIME_TARGETS="$triple" \
+          -DLLVM_HOST_TRIPLE="$triple" \
+          -DLLVM_TARGETS_TO_BUILD="host" \
+          -DRUNTIMES_BUILD_ALLOW_DARWIN=ON \
+          -DLLVM_ENABLE_ASSERTIONS=ON \
+          "-DRUNTIMES_${triple}_LIBCXXABI_ENABLE_SHARED=OFF" \
+          "-DRUNTIMES_${triple}_LIBCXX_USE_COMPILER_RT=ON" \
+          "-DRUNTIMES_${triple}_LIBCXX_PFP=tagged" \
+          "-DRUNTIMES_${triple}_LIBCXX_ENABLE_SHARED=OFF" \
+          "-DRUNTIMES_${triple}_LIBCXX_TEST_CONFIG=llvm-libc++-static.cfg.in" \
+          "-DRUNTIMES_${triple}_LIBUNWIND_ENABLE_SHARED=OFF" \
+          -DLLVM_LIT_ARGS="-sv --xunit-xml-output test-results.xml --timeout=1500 --time-tests"
+
+    # FIXME: Currently this also runs the sanitizer tests due to compiler-rt
+    # being in LLVM_ENABLE_RUNTIMES for the emulated PAC runtime. Ideally this
+    # would only run the libc++ and libc++abi tests.
+    step "Running the libc++ and libc++abi tests"
+    ${NINJA} -vC "${BUILD_DIR}" check-runtimes
+
+    # FIXME: Debugging support for PFP is incomplete so don't run the LLDB tests
+    # as above for now.
+;;
 generic-static)
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-static.cmake"
diff --git a/libcxx/utils/libcxx/test/params.py b/libcxx/utils/libcxx/test/params.py
index 81c613421a465..67201c719d1ab 100644
--- a/libcxx/utils/libcxx/test/params.py
+++ b/libcxx/utils/libcxx/test/params.py
@@ -340,6 +340,22 @@ def getSuitableClangTidy(cfg):
             ]
         )
     ),
+    Parameter(
+        name="pfp",
+        choices=["none", "untagged", "tagged"],
+        type=str,
+        default="none",
+        help="Whether to build with pointer field protection.",
+        actions=lambda pfp: [] if pfp == "none" else [
+            AddCompileFlag(f"-fexperimental-pointer-field-protection={pfp}"),
+            # Requires support for new relocations which are only implemented in lld for now.
+            AddLinkFlag("-fuse-ld=lld"),
+            # Requires emulated PAC support in compiler-rt.
+            AddCompileFlag("--rtlib=compiler-rt"),
+            AddLinkFlag("--rtlib=compiler-rt"),
+            AddLinkFlag("--unwindlib=libunwind"),
+        ],
+    ),
     Parameter(
         name="enable_experimental",
         choices=[True, False],
diff --git a/libcxxabi/test/CMakeLists.txt b/libcxxabi/test/CMakeLists.txt
index 9eabfb08240b6..447b0fc43b813 100644
--- a/libcxxabi/test/CMakeLists.txt
+++ b/libcxxabi/test/CMakeLists.txt
@@ -80,6 +80,8 @@ if (LLVM_USE_SANITIZER)
   serialize_lit_string_param(SERIALIZED_LIT_PARAMS use_sanitizer "${LLVM_USE_SANITIZER}")
 endif()
 
+serialize_lit_string_param(SERIALIZED_LIT_PARAMS pfp "${LIBCXX_PFP}")
+
 if (CMAKE_CXX_COMPILER_TARGET)
   serialize_lit_string_param(SERIALIZED_LIT_PARAMS target_triple "${CMAKE_CXX_COMPILER_TARGET}")
 else()