Index: compiler-rt/trunk/lib/asan/asan_flags.cc
===================================================================
--- compiler-rt/trunk/lib/asan/asan_flags.cc
+++ compiler-rt/trunk/lib/asan/asan_flags.cc
@@ -120,12 +120,12 @@
 #endif
 
   // Override from command line.
-  asan_parser.ParseString(GetEnv("ASAN_OPTIONS"));
+  asan_parser.ParseStringFromEnv("ASAN_OPTIONS");
 #if CAN_SANITIZE_LEAKS
-  lsan_parser.ParseString(GetEnv("LSAN_OPTIONS"));
+  lsan_parser.ParseStringFromEnv("LSAN_OPTIONS");
 #endif
 #if CAN_SANITIZE_UB
-  ubsan_parser.ParseString(GetEnv("UBSAN_OPTIONS"));
+  ubsan_parser.ParseStringFromEnv("UBSAN_OPTIONS");
 #endif
 
   InitializeCommonFlags();
Index: compiler-rt/trunk/lib/cfi/cfi.cpp
===================================================================
--- compiler-rt/trunk/lib/cfi/cfi.cpp
+++ compiler-rt/trunk/lib/cfi/cfi.cpp
@@ -372,7 +372,7 @@
 
   FlagParser cfi_parser;
   RegisterCommonFlags(&cfi_parser);
-  cfi_parser.ParseString(GetEnv("CFI_OPTIONS"));
+  cfi_parser.ParseStringFromEnv("CFI_OPTIONS");
 
 #ifdef CFI_ENABLE_DIAG
   FlagParser ubsan_parser;
@@ -381,7 +381,7 @@
 
   const char *ubsan_default_options = __ubsan::MaybeCallUbsanDefaultOptions();
   ubsan_parser.ParseString(ubsan_default_options);
-  ubsan_parser.ParseString(GetEnv("UBSAN_OPTIONS"));
+  ubsan_parser.ParseStringFromEnv("UBSAN_OPTIONS");
 #endif
 
   InitializeCommonFlags();
Index: compiler-rt/trunk/lib/dfsan/dfsan.cc
===================================================================
--- compiler-rt/trunk/lib/dfsan/dfsan.cc
+++ compiler-rt/trunk/lib/dfsan/dfsan.cc
@@ -383,7 +383,7 @@
   FlagParser parser;
   RegisterCommonFlags(&parser);
   RegisterDfsanFlags(&parser, &flags());
-  parser.ParseString(GetEnv("DFSAN_OPTIONS"));
+  parser.ParseStringFromEnv("DFSAN_OPTIONS");
   InitializeCommonFlags();
   if (Verbosity()) ReportUnrecognizedFlags();
   if (common_flags()->help) parser.PrintFlagDescriptions();
Index: compiler-rt/trunk/lib/hwasan/hwasan.cpp
===================================================================
--- compiler-rt/trunk/lib/hwasan/hwasan.cpp
+++ compiler-rt/trunk/lib/hwasan/hwasan.cpp
@@ -129,13 +129,10 @@
   ubsan_parser.ParseString(ubsan_default_options);
 #endif
 
-  const char *hwasan_options = GetEnv("HWASAN_OPTIONS");
-  parser.ParseString(hwasan_options);
+  parser.ParseStringFromEnv("HWASAN_OPTIONS");
 #if HWASAN_CONTAINS_UBSAN
-  ubsan_parser.ParseString(GetEnv("UBSAN_OPTIONS"));
+  ubsan_parser.ParseStringFromEnv("UBSAN_OPTIONS");
 #endif
-  VPrintf(1, "HWASAN_OPTIONS: %s\n",
-          hwasan_options ? hwasan_options : "<empty>");
 
   InitializeCommonFlags();
 
Index: compiler-rt/trunk/lib/lsan/lsan.cc
===================================================================
--- compiler-rt/trunk/lib/lsan/lsan.cc
+++ compiler-rt/trunk/lib/lsan/lsan.cc
@@ -76,7 +76,7 @@
   // Override from user-specified string.
   const char *lsan_default_options = MaybeCallLsanDefaultOptions();
   parser.ParseString(lsan_default_options);
-  parser.ParseString(GetEnv("LSAN_OPTIONS"));
+  parser.ParseStringFromEnv("LSAN_OPTIONS");
 
   SetVerbosity(common_flags()->verbosity);
 
Index: compiler-rt/trunk/lib/msan/msan.cc
===================================================================
--- compiler-rt/trunk/lib/msan/msan.cc
+++ compiler-rt/trunk/lib/msan/msan.cc
@@ -175,12 +175,10 @@
   ubsan_parser.ParseString(ubsan_default_options);
 #endif
 
-  const char *msan_options = GetEnv("MSAN_OPTIONS");
-  parser.ParseString(msan_options);
+  parser.ParseStringFromEnv("MSAN_OPTIONS");
 #if MSAN_CONTAINS_UBSAN
-  ubsan_parser.ParseString(GetEnv("UBSAN_OPTIONS"));
+  ubsan_parser.ParseStringFromEnv("UBSAN_OPTIONS");
 #endif
-  VPrintf(1, "MSAN_OPTIONS: %s\n", msan_options ? msan_options : "<empty>");
 
   InitializeCommonFlags();
 
Index: compiler-rt/trunk/lib/sanitizer_common/sancov_flags.cc
===================================================================
--- compiler-rt/trunk/lib/sanitizer_common/sancov_flags.cc
+++ compiler-rt/trunk/lib/sanitizer_common/sancov_flags.cc
@@ -49,7 +49,7 @@
   RegisterSancovFlags(&parser, f);
 
   parser.ParseString(MaybeCallSancovDefaultOptions());
-  parser.ParseString(GetEnv("SANCOV_OPTIONS"));
+  parser.ParseStringFromEnv("SANCOV_OPTIONS");
 
   ReportUnrecognizedFlags();
   if (f->help) parser.PrintFlagDescriptions();
Index: compiler-rt/trunk/lib/sanitizer_common/sanitizer_flag_parser.h
===================================================================
--- compiler-rt/trunk/lib/sanitizer_common/sanitizer_flag_parser.h
+++ compiler-rt/trunk/lib/sanitizer_common/sanitizer_flag_parser.h
@@ -124,7 +124,8 @@
   FlagParser();
   void RegisterHandler(const char *name, FlagHandlerBase *handler,
                        const char *desc);
-  void ParseString(const char *s);
+  void ParseString(const char *s, const char *env_name = 0);
+  void ParseStringFromEnv(const char *env_name);
   bool ParseFile(const char *path, bool ignore_missing);
   void PrintFlagDescriptions();
 
@@ -134,8 +135,8 @@
   void fatal_error(const char *err);
   bool is_space(char c);
   void skip_whitespace();
-  void parse_flags();
-  void parse_flag();
+  void parse_flags(const char *env_option_name);
+  void parse_flag(const char *env_option_name);
   bool run_handler(const char *name, const char *value);
   char *ll_strndup(const char *s, uptr n);
 };
Index: compiler-rt/trunk/lib/sanitizer_common/sanitizer_flag_parser.cc
===================================================================
--- compiler-rt/trunk/lib/sanitizer_common/sanitizer_flag_parser.cc
+++ compiler-rt/trunk/lib/sanitizer_common/sanitizer_flag_parser.cc
@@ -62,7 +62,7 @@
 }
 
 void FlagParser::fatal_error(const char *err) {
-  Printf("ERROR: %s\n", err);
+  Printf("%s: ERROR: %s\n", SanitizerToolName, err);
   Die();
 }
 
@@ -75,10 +75,17 @@
   while (is_space(buf_[pos_])) ++pos_;
 }
 
-void FlagParser::parse_flag() {
+void FlagParser::parse_flag(const char *env_option_name) {
   uptr name_start = pos_;
   while (buf_[pos_] != 0 && buf_[pos_] != '=' && !is_space(buf_[pos_])) ++pos_;
-  if (buf_[pos_] != '=') fatal_error("expected '='");
+  if (buf_[pos_] != '=') {
+    if (env_option_name) {
+      Printf("%s: ERROR: expected '=' in %s\n", SanitizerToolName,
+             env_option_name);
+      Die();
+    } else
+      fatal_error("expected '='");
+  }
   char *name = ll_strndup(buf_ + name_start, pos_ - name_start);
 
   uptr value_start = ++pos_;
@@ -100,11 +107,11 @@
   if (!res) fatal_error("Flag parsing failed.");
 }
 
-void FlagParser::parse_flags() {
+void FlagParser::parse_flags(const char *env_option_name) {
   while (true) {
     skip_whitespace();
     if (buf_[pos_] == 0) break;
-    parse_flag();
+    parse_flag(env_option_name);
   }
 
   // Do a sanity check for certain flags.
@@ -112,7 +119,13 @@
     common_flags_dont_use.malloc_context_size = 1;
 }
 
-void FlagParser::ParseString(const char *s) {
+void FlagParser::ParseStringFromEnv(const char *env_name) {
+  const char *env = GetEnv(env_name);
+  VPrintf(1, "%s: %s\n", env_name, env ? env : "<empty>");
+  ParseString(env, env_name);
+}
+
+void FlagParser::ParseString(const char *s, const char *env_option_name) {
   if (!s) return;
   // Backup current parser state to allow nested ParseString() calls.
   const char *old_buf_ = buf_;
@@ -120,7 +133,7 @@
   buf_ = s;
   pos_ = 0;
 
-  parse_flags();
+  parse_flags(env_option_name);
 
   buf_ = old_buf_;
   pos_ = old_pos_;
@@ -139,7 +152,7 @@
     Printf("Failed to read options from '%s': error %d\n", path, err);
     return false;
   }
-  ParseString(data);
+  ParseString(data, path);
   UnmapOrDie(data, data_mapped_size);
   return true;
 }
Index: compiler-rt/trunk/lib/scudo/scudo_flags.cpp
===================================================================
--- compiler-rt/trunk/lib/scudo/scudo_flags.cpp
+++ compiler-rt/trunk/lib/scudo/scudo_flags.cpp
@@ -68,7 +68,7 @@
   ScudoParser.ParseString(getScudoDefaultOptions());
 
   // Override from environment.
-  ScudoParser.ParseString(GetEnv("SCUDO_OPTIONS"));
+  ScudoParser.ParseStringFromEnv("SCUDO_OPTIONS");
 
   InitializeCommonFlags();
 
Index: compiler-rt/trunk/lib/tsan/dd/dd_rtl.cc
===================================================================
--- compiler-rt/trunk/lib/tsan/dd/dd_rtl.cc
+++ compiler-rt/trunk/lib/tsan/dd/dd_rtl.cc
@@ -83,7 +83,7 @@
   FlagParser parser;
   RegisterFlag(&parser, "second_deadlock_stack", "", &f->second_deadlock_stack);
   RegisterCommonFlags(&parser);
-  parser.ParseString(GetEnv("DSAN_OPTIONS"));
+  parser.ParseStringFromEnv("DSAN_OPTIONS");
   SetVerbosity(common_flags()->verbosity);
 }
 
Index: compiler-rt/trunk/lib/tsan/rtl/tsan_flags.h
===================================================================
--- compiler-rt/trunk/lib/tsan/rtl/tsan_flags.h
+++ compiler-rt/trunk/lib/tsan/rtl/tsan_flags.h
@@ -27,7 +27,8 @@
   void ParseFromString(const char *str);
 };
 
-void InitializeFlags(Flags *flags, const char *env);
+void InitializeFlags(Flags *flags, const char *env,
+                     const char *env_option_name = nullptr);
 }  // namespace __tsan
 
 #endif  // TSAN_FLAGS_H
Index: compiler-rt/trunk/lib/tsan/rtl/tsan_flags.cc
===================================================================
--- compiler-rt/trunk/lib/tsan/rtl/tsan_flags.cc
+++ compiler-rt/trunk/lib/tsan/rtl/tsan_flags.cc
@@ -49,7 +49,7 @@
       &f->second_deadlock_stack);
 }
 
-void InitializeFlags(Flags *f, const char *env) {
+void InitializeFlags(Flags *f, const char *env, const char *env_option_name) {
   SetCommonFlagsDefaults();
   {
     // Override some common flags defaults.
@@ -91,9 +91,9 @@
   ubsan_parser.ParseString(ubsan_default_options);
 #endif
   // Override from command line.
-  parser.ParseString(env);
+  parser.ParseString(env, env_option_name);
 #if TSAN_CONTAINS_UBSAN
-  ubsan_parser.ParseString(GetEnv("UBSAN_OPTIONS"));
+  ubsan_parser.ParseStringFromEnv("UBSAN_OPTIONS");
 #endif
 
   // Sanity check.
Index: compiler-rt/trunk/lib/tsan/rtl/tsan_rtl.cc
===================================================================
--- compiler-rt/trunk/lib/tsan/rtl/tsan_rtl.cc
+++ compiler-rt/trunk/lib/tsan/rtl/tsan_rtl.cc
@@ -350,10 +350,11 @@
   SetCheckFailedCallback(TsanCheckFailed);
 
   ctx = new(ctx_placeholder) Context;
-  const char *options = GetEnv(SANITIZER_GO ? "GORACE" : "TSAN_OPTIONS");
+  const char *env_name = SANITIZER_GO ? "GORACE" : "TSAN_OPTIONS";
+  const char *options = GetEnv(env_name);
   CacheBinaryName();
   CheckASLR();
-  InitializeFlags(&ctx->flags, options);
+  InitializeFlags(&ctx->flags, options, env_name);
   AvoidCVE_2016_2143();
   __sanitizer::InitializePlatformEarly();
   __tsan::InitializePlatformEarly();
Index: compiler-rt/trunk/lib/ubsan/ubsan_flags.cc
===================================================================
--- compiler-rt/trunk/lib/ubsan/ubsan_flags.cc
+++ compiler-rt/trunk/lib/ubsan/ubsan_flags.cc
@@ -69,7 +69,7 @@
   // Override from user-specified string.
   parser.ParseString(MaybeCallUbsanDefaultOptions());
   // Override from environment variable.
-  parser.ParseString(GetFlag("UBSAN_OPTIONS"));
+  parser.ParseStringFromEnv("UBSAN_OPTIONS");
   InitializeCommonFlags();
   if (Verbosity()) ReportUnrecognizedFlags();
 
Index: compiler-rt/trunk/lib/xray/xray_flags.cc
===================================================================
--- compiler-rt/trunk/lib/xray/xray_flags.cc
+++ compiler-rt/trunk/lib/xray/xray_flags.cc
@@ -68,7 +68,7 @@
   XRayParser.ParseString(XRayCompileFlags);
 
   // Override from environment variables.
-  XRayParser.ParseString(GetEnv("XRAY_OPTIONS"));
+  XRayParser.ParseStringFromEnv("XRAY_OPTIONS");
 
   // Override from command line.
   InitializeCommonFlags();