Make lsan complain loudly when running under ptrace

[kcc]

Summary

LeakSanitizer does not work with ptrace but currently it
will print warnings (only under verbosity=1) and then proceed
to print tons of false reports.
This patch makes lsan fail hard under ptrace with a verbose message.

https://github.com/google/sanitizers/issues/728

[aizatsky]

Thanks.

[thakis]

test/lsan/TestCases/strace_test.cc

3

Apparently strace doesn't exist on all the bots:

http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-debian-fast/builds/971/steps/test/logs/stdio

/home/llvmbb/llvm-build-dir/llvm-clang-lld-x86_64-debian-fast/llvm.src/projects/compiler-rt/test/lsan/TestCases/strace_test.cc:13:11: error: expected string not found in input
// CHECK: LeakSanitizer has encountered a fatal error
          ^
<stdin>:1:1: note: scanning from here
Error: Unable to find `strace' in PATH: No such file or directory

Maybe this needs a "requires:" line, or that bot needs strace installed. (Not sure, and not my bot, so I don't care much, just happened to see it.)

lib/lsan/lsan_common.cc

static bool CheckForLeaks() {
   UnlockAllocator();
   UnlockThreadRegistry();
 
   if (!param.success) {
     Report("LeakSanitizer has encountered a fatal error.\n");
     Report(
         "HINT: For debugging, try setting environment variable "
         "LSAN_OPTIONS=verbosity=1:log_threads=1\n");
+    Report(
+        "HINT: LeakSanitizer does not work under ptrace (strace, gdb, etc)\n");
     Die();
   }
   param.leak_report.ApplySuppressions();
   uptr unsuppressed_count = param.leak_report.UnsuppressedLeakCount();
   if (unsuppressed_count > 0) {
     Decorator d;
     Printf("\n"
            "================================================================="

lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc

void ThreadSuspender::KillAllThreads() {
   for (uptr i = 0; i < suspended_threads_list_.thread_count(); i++)
     internal_ptrace(PTRACE_KILL, suspended_threads_list_.GetThreadID(i),
                     nullptr, nullptr);
 }
 
 bool ThreadSuspender::SuspendAllThreads() {
   ThreadLister thread_lister(pid_);
   bool added_threads;
+  bool first_iteration = true;
   do {
     // Run through the directory entries once.
     added_threads = false;
     pid_t tid = thread_lister.GetNextTID();
     while (tid >= 0) {
       if (SuspendThread(tid))
         added_threads = true;
       tid = thread_lister.GetNextTID();
     }
-    if (thread_lister.error()) {
+    if (thread_lister.error() || (first_iteration && !added_threads)) {
       // Detach threads and fail.
       ResumeAllThreads();
       return false;
     }
     thread_lister.Reset();
+    first_iteration = false;
   } while (added_threads);
   return true;
 }
 
 // Pointer to the ThreadSuspender instance for use in signal handler.
 static ThreadSuspender *thread_suspender_instance = nullptr;
 
 // Synchronous signals that should not be blocked.

test/lsan/TestCases/strace_test.cc

+// Test that lsan reports a proper error when running under strace.
+// RUN: %clangxx_lsan %s -o %t
+// RUN: not strace -o /dev/null %run %t 2>&1 | FileCheck %s
+
+#include <stdio.h>
+#include <stdlib.h>
+
+static volatile void *sink;
+
+int main() {
+  sink = malloc(42);
+}
+// CHECK: LeakSanitizer has encountered a fatal error
+// CHECK: HINT: LeakSanitizer does not work under ptrace (strace, gdb, etc)