[ubsan] Add preinit initializer for ubsan

Summary:
Now that ubsan does function interception (for signals), we
need to ensure that ubsan is initialized before any library
constructors are called. Otherwise, if a constructor calls
sigaction, ubsan will intercept in an unitialized state, which
will cause a crash.

This patch is a partial revert of r317757, which removed
preinit arrays for ubsan.

Reviewers: vitalybuka, eugenis, pcc

Subscribers: kubamracek, mgorny, llvm-commits, #sanitizers

Differential Revision: https://reviews.llvm.org/D42389

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@323249 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 48 insertions, 2 deletions

diff --git a/lib/ubsan/CMakeLists.txt b/lib/ubsan/CMakeLists.txt
index ea4f6e895..911bd3ebc 100644
--- a/lib/ubsan/CMakeLists.txt
+++ b/lib/ubsan/CMakeLists.txt
@@ -151,6 +151,7 @@ else()
     add_compiler_rt_runtime(clang_rt.ubsan_standalone
       STATIC
       ARCHS ${UBSAN_SUPPORTED_ARCH}
+      SOURCES ubsan_init_standalone_preinit.cc
       OBJECT_LIBS RTSanitizerCommon
               RTSanitizerCommonLibc
               RTUbsan
diff --git a/lib/ubsan/ubsan_flags.cc b/lib/ubsan/ubsan_flags.cc
index c4fb278c8..7b6784b82 100644
--- a/lib/ubsan/ubsan_flags.cc
+++ b/lib/ubsan/ubsan_flags.cc
@@ -26,6 +26,15 @@ const char *MaybeCallUbsanDefaultOptions() {
   return (&__ubsan_default_options) ? __ubsan_default_options() : "";
 }
 
+static const char *GetFlag(const char *flag) {
+  // We cannot call getenv() from inside a preinit array initializer
+  if (SANITIZER_CAN_USE_PREINIT_ARRAY) {
+    return GetEnv(flag);
+  } else {
+    return getenv(flag);
+  }
+}
+
 Flags ubsan_flags;
 
 void Flags::SetDefaults() {
@@ -47,7 +56,7 @@ void InitializeFlags() {
     CommonFlags cf;
     cf.CopyFrom(*common_flags());
     cf.print_summary = false;
-    cf.external_symbolizer_path = getenv("UBSAN_SYMBOLIZER_PATH");
+    cf.external_symbolizer_path = GetFlag("UBSAN_SYMBOLIZER_PATH");
     OverrideCommonFlags(cf);
   }
 
@@ -61,7 +70,7 @@ void InitializeFlags() {
   // Override from user-specified string.
   parser.ParseString(MaybeCallUbsanDefaultOptions());
   // Override from environment variable.
-  parser.ParseString(getenv("UBSAN_OPTIONS"));
+  parser.ParseString(GetFlag("UBSAN_OPTIONS"));
   InitializeCommonFlags();
   if (Verbosity()) ReportUnrecognizedFlags();
 
diff --git a/lib/ubsan/ubsan_init_standalone_preinit.cc b/lib/ubsan/ubsan_init_standalone_preinit.cc
new file mode 100644
index 000000000..5e75c17ae
--- /dev/null
+++ b/lib/ubsan/ubsan_init_standalone_preinit.cc
@@ -0,0 +1,36 @@
+//===-- ubsan_init_standalone_preinit.cc ---------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Initialization of standalone UBSan runtime.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ubsan_platform.h"
+#if !CAN_SANITIZE_UB
+#error "UBSan is not supported on this platform!"
+#endif
+
+#include "sanitizer_common/sanitizer_internal_defs.h"
+#include "ubsan_init.h"
+#include "ubsan_signals_standalone.h"
+
+#if SANITIZER_CAN_USE_PREINIT_ARRAY
+
+namespace __ubsan {
+
+static void PreInitAsStandalone() {
+  InitAsStandalone();
+  InitializeDeadlySignals();
+}
+
+} // namespace __ubsan
+
+__attribute__((section(".preinit_array"), used)) void (*__local_ubsan_preinit)(
+    void) = __ubsan::PreInitAsStandalone;
+#endif // SANITIZER_CAN_USE_PREINIT_ARRAY