[compiler-rt][libFuzzer] Add support for capturing SIGTRAP exits. (#149120)

Swift's FatalError raises a SIGTRAP, which currently causes the fuzzer
to exit without writing out the crashing input.

rdar://142975522

compiler-rt/lib/fuzzer/FuzzerDriver.cpp

@@ -834,6 +834,7 @@ int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
   Options.HandleInt = Flags.handle_int;
   Options.HandleSegv = Flags.handle_segv;
   Options.HandleTerm = Flags.handle_term;
+  Options.HandleTrap = Flags.handle_trap;
   Options.HandleXfsz = Flags.handle_xfsz;
   Options.HandleUsr1 = Flags.handle_usr1;
   Options.HandleUsr2 = Flags.handle_usr2;

compiler-rt/lib/fuzzer/FuzzerFlags.def

@@ -152,6 +152,7 @@ FUZZER_FLAG_INT(handle_ill, 1, "If 1, try to intercept SIGILL.")
 FUZZER_FLAG_INT(handle_fpe, 1, "If 1, try to intercept SIGFPE.")
 FUZZER_FLAG_INT(handle_int, 1, "If 1, try to intercept SIGINT.")
 FUZZER_FLAG_INT(handle_term, 1, "If 1, try to intercept SIGTERM.")
+FUZZER_FLAG_INT(handle_trap, 1, "If 1, try to intercept SIGTRAP.")
 FUZZER_FLAG_INT(handle_xfsz, 1, "If 1, try to intercept SIGXFSZ.")
 FUZZER_FLAG_INT(handle_usr1, 1, "If 1, try to intercept SIGUSR1.")
 FUZZER_FLAG_INT(handle_usr2, 1, "If 1, try to intercept SIGUSR2.")

compiler-rt/lib/fuzzer/FuzzerOptions.h

@@ -82,6 +82,7 @@ struct FuzzingOptions {
   bool HandleInt = false;
   bool HandleSegv = false;
   bool HandleTerm = false;
+  bool HandleTrap = false;
   bool HandleXfsz = false;
   bool HandleUsr1 = false;
   bool HandleUsr2 = false;

compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp

@@ -410,7 +410,7 @@ void SetSignalHandler(const FuzzingOptions &Options) {
 
   // Early exit if no crash handler needed.
   if (!Options.HandleSegv && !Options.HandleBus && !Options.HandleIll &&
-      !Options.HandleFpe && !Options.HandleAbrt)
+      !Options.HandleFpe && !Options.HandleAbrt && !Options.HandleTrap)
     return;
 
   // Set up the crash handler and wait until it is ready before proceeding.

compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp

@@ -132,6 +132,8 @@ void SetSignalHandler(const FuzzingOptions& Options) {
     SetSigaction(SIGILL, CrashHandler);
   if (Options.HandleFpe)
     SetSigaction(SIGFPE, CrashHandler);
+  if (Options.HandleTrap)
+    SetSigaction(SIGTRAP, CrashHandler);
   if (Options.HandleXfsz)
     SetSigaction(SIGXFSZ, FileSizeExceedHandler);
   if (Options.HandleUsr1)

compiler-rt/test/fuzzer/SigTrapTest.cpp

@@ -0,0 +1,29 @@
+// 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
+
+// Simple test for a fuzzer. The fuzzer must find the string "Hi!".
+#include <assert.h>
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <ostream>
+#include <signal.h>
+
+static volatile int Sink;
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  assert(Data);
+  if (Size > 0 && Data[0] == 'H') {
+    Sink = 1;
+    if (Size > 1 && Data[1] == 'i') {
+      Sink = 2;
+      if (Size > 2 && Data[2] == '!') {
+        std::cout << "BINGO; Found the target, exiting\n" << std::flush;
+        raise(SIGTRAP);
+      }
+    }
+  }
+  return 0;
+}

compiler-rt/test/fuzzer/sig-trap.test

@@ -0,0 +1,7 @@
+RUN: %cpp_compiler %S/SigTrapTest.cpp -o %t
+
+RUN: not %run %t            2>&1 | FileCheck %s
+CHECK: BINGO
+CHECK: ERROR: libFuzzer: deadly signal
+
+RUN: trap "%run %t -handle_trap=0" TRAP