Index: lib/asan/asan_flags.h
===================================================================
--- lib/asan/asan_flags.h
+++ lib/asan/asan_flags.h
@@ -65,6 +65,7 @@
   int detect_invalid_pointer_pairs;
   bool detect_container_overflow;
   int detect_odr_violation;
+  bool dump_instruction_bytes;
 };
 
 extern Flags asan_flags_dont_use_directly;
Index: lib/asan/asan_report.cc
===================================================================
--- lib/asan/asan_report.cc
+++ lib/asan/asan_report.cc
@@ -86,15 +86,24 @@
     }
   }
   const char *EndShadowByte() { return Default(); }
+  const char *MemoryByte() { return Magenta(); }
+  const char *EndMemoryByte() { return Default(); }
 };
 
 // ---------------------- Helper functions ----------------------- {{{1
 
-static void PrintShadowByte(InternalScopedString *str, const char *before,
-                            u8 byte, const char *after = "\n") {
+static void PrintMemoryByte(InternalScopedString *str, const char *before,
+    u8 byte, bool in_shadow, const char *after = "\n") {
   Decorator d;
-  str->append("%s%s%x%x%s%s", before, d.ShadowByte(byte), byte >> 4, byte & 15,
-              d.EndShadowByte(), after);
+  str->append("%s%s%x%x%s%s", before,
+              in_shadow ? d.ShadowByte(byte) : d.MemoryByte(),
+              byte >> 4, byte & 15,
+              in_shadow ? d.EndShadowByte() : d.EndMemoryByte(), after);
+}
+
+static void PrintShadowByte(InternalScopedString *str, const char *before,
+    u8 byte, const char *after = "\n") {
+  PrintMemoryByte(str, before, byte, /*in_shadow*/true, after);
 }
 
 static void PrintShadowBytes(InternalScopedString *str, const char *before,
@@ -149,6 +158,20 @@
   PrintShadowByte(str, "  ASan internal:           ", kAsanInternalHeapMagic);
 }
 
+void MaybeDumpInstructionBytes(uptr pc) {
+  if (!flags()->dump_instruction_bytes)
+    return;
+  InternalScopedString str(1024);
+  if (pc >= GetPageSizeCached()) {
+    str.append("First 16 instruction bytes at pc: ");
+    for (int i = 0; i < 16; ++i) {
+      PrintMemoryByte(&str, "", ((char *)pc)[i], /*in_shadow*/false, " ");
+    }
+    str.append("\n");
+    Report("%s", str.data());
+  }
+}
+
 static void PrintShadowMemoryForAddress(uptr addr) {
   if (!AddrIsInMem(addr)) return;
   uptr shadow_addr = MemToShadow(addr);
@@ -630,9 +653,13 @@
       " (pc %p bp %p sp %p T%d)\n",
       description, (void *)addr, (void *)pc, (void *)bp, (void *)sp,
       GetCurrentTidOrInvalid());
+  if (pc < GetPageSizeCached()) {
+    Report("Hint: pc points to the zero page.\n");
+  }
   Printf("%s", d.EndWarning());
   GET_STACK_TRACE_SIGNAL(pc, bp, context);
   stack.Print();
+  MaybeDumpInstructionBytes(pc);
   Printf("AddressSanitizer can not provide additional info.\n");
   ReportErrorSummary("SEGV", &stack);
 }
Index: lib/asan/asan_rtl.cc
===================================================================
--- lib/asan/asan_rtl.cc
+++ lib/asan/asan_rtl.cc
@@ -230,6 +230,9 @@
             "If >=2, detect violation of One-Definition-Rule (ODR); "
             "If ==1, detect ODR-violation only if the two variables "
             "have different sizes");
+
+  ParseFlag(str, &f->dump_instruction_bytes, "dump_instruction_bytes",
+      "If true, dump 16 bytes starting at the instruction that caused SEGV");
 }
 
 void InitializeFlags(Flags *f, const char *env) {
Index: lib/sanitizer_common/sanitizer_posix_libcdep.cc
===================================================================
--- lib/sanitizer_common/sanitizer_posix_libcdep.cc
+++ lib/sanitizer_common/sanitizer_posix_libcdep.cc
@@ -148,7 +148,9 @@
   struct sigaction sigact;
   internal_memset(&sigact, 0, sizeof(sigact));
   sigact.sa_sigaction = (sa_sigaction_t)handler;
-  sigact.sa_flags = SA_SIGINFO;
+  // Do not block the signal from being received in that signal's handler.
+  // Clients are responsible for handling this correctly.
+  sigact.sa_flags = SA_SIGINFO | SA_NODEFER;
   if (common_flags()->use_sigaltstack) sigact.sa_flags |= SA_ONSTACK;
   CHECK_EQ(0, internal_sigaction(signum, &sigact, 0));
   VReport(1, "Installed the sigaction for signal %d\n", signum);
Index: test/asan/TestCases/dump_instruction_bytes.cc
===================================================================
--- test/asan/TestCases/dump_instruction_bytes.cc
+++ test/asan/TestCases/dump_instruction_bytes.cc
@@ -0,0 +1,22 @@
+// Check that ASan prints the faulting instruction bytes on
+// dump_instruction_bytes=1
+// RUN: %clangxx_asan  %s -o %t
+// RUN: env ASAN_OPTIONS=dump_instruction_bytes=1 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-DUMP
+// RUN: not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-NODUMP
+
+int main() {
+#if defined(__x86_64__)
+  asm("movq $0, %rax");
+  asm("movl $0xcafebabe, 0x0(%rax)");
+#elif defined(i386)
+  asm("movl $0, %eax");
+  asm("movl $0xcafebabe, 0x0(%eax)");
+#elif defined(__arm__)
+  asm("mov %r0, $0xcafebabe");
+  asm("mov %r1, $0x0");
+  asm("str %r0, [%r1]");
+#endif
+  // CHECK-DUMP: First 16 instruction bytes at pc: c7 00 be ba fe ca
+  // CHECK-NODUMP-NOT: First 16 instruction bytes
+  return 0;
+}
Index: test/asan/TestCases/zero_page_pc.cc
===================================================================
--- test/asan/TestCases/zero_page_pc.cc
+++ test/asan/TestCases/zero_page_pc.cc
@@ -0,0 +1,11 @@
+// Check that ASan correctly detects SEGV on the zero page.
+// RUN: %clangxx_asan %s -o %t && not %run %t 2>&1 | FileCheck %s
+
+typedef void void_f();
+int main() {
+  void_f *func = (void_f *)0x7;
+  func();
+  // CHECK: {{AddressSanitizer: SEGV.*(pc.*0007)}}
+  // CHECK: Hint: pc points to the zero page.
+  return 0;
+}