[nsan] Add nsan_preinit.cpp and make it static library only

[MaskRay]

#94322 defines .preinit_array to initialize nsan early.
DT_PREINIT_ARRAY can only be used with the main executable. GNU ld would
complain when a DSO has .preinit_array. Therefore,
nsan_preinit.cpp cannot be linked into libclang_rt.nsan.so (#98415).

Working with @alexander-shaposhnikov, we noticed that Nsan-x86_64-Test --gtest_output=json without .preinit_array will sigsegv. This is
because googletest with the JSON output calls localtime_r , which
calls free(0) and fails when REAL(free) remains uninitialized
(nullptr). This is benign with the default output because malloc/free
are all paired and REAL(free)(ptr) is not called.

To fix the unittest failure, __nsan_init needs to be called early
(.preinit_array).
asan/tests/CMakeLists.txt:ASAN_UNITTEST_INSTRUMENTED_LINK_FLAGS ues
-fsanitize=address to ensure asan_preinit.cpp.o is linked into the
unittest executable. Port the approach and remove
NSAN_TEST_RUNTIME_OBJECTS.

Fix #98523

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Fangrui Song (MaskRay)

Changes

#94322 defines .preinit_array to initialize nsan early.
DT_PREINIT_ARRAY can only be used with the main executable. GNU ld would
complain when a DSO has .preinit_array. Therefore,
nsan_preinit.cpp cannot be linked into libclang_rt.nsan.so.

Working with @alexander-shaposhnikov, we noticed that Nsan-x86_64-Test --gtest_output=json without .preinit_array will sigsegv.
This is because googletest calls timing functions, which call free (intercepted).
__nsan_init needs to be called early (.preinit_array) to make the
free interceptor work.

The robust way to ensure nsan_preinit.cpp.o is used is to link the
unittest executable with -fsanitize=numerical and remove
NSAN_TEST_RUNTIME_OBJECTS.

---

Full diff: https://github.com/llvm/llvm-project/pull/98564.diff

5 Files Affected:

• (modified) compiler-rt/lib/nsan/CMakeLists.txt (+10-1)
• (modified) compiler-rt/lib/nsan/nsan.cpp (-5)
• (modified) compiler-rt/lib/nsan/nsan.h (+2)
• (added) compiler-rt/lib/nsan/nsan_preinit.cpp (+21)
• (modified) compiler-rt/lib/nsan/tests/CMakeLists.txt (+3-18)

diff --git a/compiler-rt/lib/nsan/CMakeLists.txt b/compiler-rt/lib/nsan/CMakeLists.txt
index d67c3ac434d3a..1e138d4560c89 100644
--- a/compiler-rt/lib/nsan/CMakeLists.txt
+++ b/compiler-rt/lib/nsan/CMakeLists.txt
@@ -11,6 +11,9 @@ set(NSAN_SOURCES
   nsan_suppressions.cpp
 )
 
+set(NSAN_PREINIT_SOURCES
+  nsan_preinit.cpp)
+
 set(NSAN_HEADERS
   nsan.h
   nsan_flags.h
@@ -61,6 +64,12 @@ if(NOT APPLE)
       ADDITIONAL_HEADERS ${NSAN_HEADERS}
       CFLAGS ${NSAN_CFLAGS})
 
+  add_compiler_rt_object_libraries(RTNsan_preinit
+    ARCHS ${NSAN_SUPPORTED_ARCH}
+    SOURCES ${NSAN_PREINIT_SOURCES}
+    ADDITIONAL_HEADERS ${NSAN_HEADERS}
+    CFLAGS ${NSAN_CFLAGS})
+
   file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/dummy.cpp "")
   add_compiler_rt_object_libraries(RTNsan_dynamic_version_script_dummy
     ARCHS ${NSAN_SUPPORTED_ARCH}
@@ -72,7 +81,7 @@ add_compiler_rt_runtime(
   clang_rt.nsan
   STATIC
   ARCHS ${NSAN_SUPPORTED_ARCH}
-  OBJECT_LIBS RTNsan
+  OBJECT_LIBS RTNsan_preinit RTNsan
               ${NSAN_COMMON_RUNTIME_OBJECT_LIBS}
   CFLAGS ${NSAN_CFLAGS}
   PARENT_TARGET nsan)
diff --git a/compiler-rt/lib/nsan/nsan.cpp b/compiler-rt/lib/nsan/nsan.cpp
index f7b2ce2048290..7a5f013579dfb 100644
--- a/compiler-rt/lib/nsan/nsan.cpp
+++ b/compiler-rt/lib/nsan/nsan.cpp
@@ -801,8 +801,3 @@ extern "C" SANITIZER_INTERFACE_ATTRIBUTE void __nsan_init() {
   nsan_init_is_running = false;
   nsan_initialized = true;
 }
-
-#if SANITIZER_CAN_USE_PREINIT_ARRAY
-__attribute__((section(".preinit_array"),
-               used)) static void (*nsan_init_ptr)() = __nsan_init;
-#endif
diff --git a/compiler-rt/lib/nsan/nsan.h b/compiler-rt/lib/nsan/nsan.h
index 0fb998b049854..8277e3d778047 100644
--- a/compiler-rt/lib/nsan/nsan.h
+++ b/compiler-rt/lib/nsan/nsan.h
@@ -32,6 +32,8 @@ using __sanitizer::uptr;
 // Private nsan interface. Used e.g. by interceptors.
 extern "C" {
 
+void __nsan_init();
+
 // This marks the shadow type of the given block of application memory as
 // unknown.
 // printf-free (see comment in nsan_interceptors.cc).
diff --git a/compiler-rt/lib/nsan/nsan_preinit.cpp b/compiler-rt/lib/nsan/nsan_preinit.cpp
new file mode 100644
index 0000000000000..5d869bbdf9668
--- /dev/null
+++ b/compiler-rt/lib/nsan/nsan_preinit.cpp
@@ -0,0 +1,21 @@
+//===- nsan_preinit.cpp ---------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Call __nsan_init early using ELF DT_PREINIT_ARRAY.
+//
+//===----------------------------------------------------------------------===//
+
+#include "nsan/nsan.h"
+#include "sanitizer_common/sanitizer_internal_defs.h"
+
+#if SANITIZER_CAN_USE_PREINIT_ARRAY
+
+__attribute__((section(".preinit_array"), used)) static auto nsan_preinit =
+    __nsan_init;
+
+#endif
diff --git a/compiler-rt/lib/nsan/tests/CMakeLists.txt b/compiler-rt/lib/nsan/tests/CMakeLists.txt
index e472fc5c06f90..ecb1aa9c56cf2 100644
--- a/compiler-rt/lib/nsan/tests/CMakeLists.txt
+++ b/compiler-rt/lib/nsan/tests/CMakeLists.txt
@@ -15,6 +15,8 @@ set(NSAN_UNITTEST_LINK_FLAGS
   ${COMPILER_RT_UNITTEST_LINK_FLAGS}
   ${COMPILER_RT_UNWINDER_LINK_LIBS}
   ${SANITIZER_TEST_CXX_LIBRARIES})
+set(NSAN_UNITTEST_INSTRUMENTED_LINK_FLAGS ${NSAN_UNITTEST_LINK_FLAGS})
+list(APPEND NSAN_UNITTEST_INSTRUMENTED_LINK_FLAGS -fsanitize=numerical)
 
 file(GLOB NSAN_HEADERS ../*.h)
 set(NSAN_UNITTESTS
@@ -27,30 +29,13 @@ if(COMPILER_RT_DEFAULT_TARGET_ARCH IN_LIST NSAN_SUPPORTED_ARCH)
   # NSan unit tests are only run on the host machine.
   set(arch ${COMPILER_RT_DEFAULT_TARGET_ARCH})
 
-  set(NSAN_TEST_RUNTIME RTNsanTest.${arch})
-
-  set(NSAN_TEST_RUNTIME_OBJECTS
-    $<TARGET_OBJECTS:RTNsan.${arch}>
-    $<TARGET_OBJECTS:RTInterception.${arch}>
-    $<TARGET_OBJECTS:RTSanitizerCommon.${arch}>
-    $<TARGET_OBJECTS:RTSanitizerCommonLibc.${arch}>
-    $<TARGET_OBJECTS:RTSanitizerCommonSymbolizer.${arch}>)
-
-  add_library(${NSAN_TEST_RUNTIME} STATIC
-    ${NSAN_TEST_RUNTIME_OBJECTS})
-
-  set_target_properties(${NSAN_TEST_RUNTIME} PROPERTIES
-    ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
-    FOLDER "Compiler-RT Runtime tests")
-
   set(NsanTestObjects)
   generate_compiler_rt_tests(NsanTestObjects
     NsanUnitTests "Nsan-${arch}-Test" ${arch}
     SOURCES ${NSAN_UNITTESTS} ${COMPILER_RT_GTEST_SOURCE}
-    RUNTIME ${NSAN_TEST_RUNTIME}
     DEPS ${NSAN_UNIT_TEST_HEADERS}
     CFLAGS ${NSAN_UNITTEST_CFLAGS}
-    LINK_FLAGS ${NSAN_UNITTEST_LINK_FLAGS})
+    LINK_FLAGS ${NSAN_UNITTEST_INSTRUMENTED_LINK_FLAGS})
   set_target_properties(NsanUnitTests PROPERTIES
     RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
 endif()

[alexander-shaposhnikov]

Thanks! I guess this PR resolves #98523 and the issues reported on #98415 .