[tsan] Implement __tsan_get_alloc_stack and __tsan_locate_address to query pointer types and allocation stacks of heap pointers

[kubamracek]

Summary

In ASan, we have __asan_locate_address and __asan_get_alloc_stack, which is used in LLDB/Xcode to show the allocation backtrace for a heap memory object. This patch implements the same for TSan.

[dvyukov]

lib/tsan/rtl/tsan_debugging.cc

168

Since the interface is different from asan, it may makes sense to return block begin and size as well. What do you think?

181

os_id can be stale if status is not ThreadStatusRunning
I think it's better to return something more predictable in such case, e.g. 0.

[kubamracek]

lib/tsan/rtl/tsan_debugging.cc

168

Makes sense. What about going further and adding a TSan version of __asan_locate_address (see asan_debugging.cc), which will "describe" a pointer and return its bounds if known, i.e. having two APIs:

__tsan_locate_address(addr) ... returns region name, start address, block size
__tsan_get_alloc_stack(addr) ... returns trace, thread ID

Does that sound better or worse than having just one

__tsan_get_alloc_stack(addr) ... returns trace, thread ID, start address and block size

?

181

Hm. At least on Darwin, GetTid() returns a unique ID for the current boot of the OS. So it's correct even after the thread finished, and even after the process has ended (as long as you don't reboot). Is gettid() on Linux different?

I'm already using os_id to "match" threads in TSan reports: If we see the same os_id, we know it's the same thread even when that thread doesn't exist anymore. I'd like not to lose this feature.

Does Linux reuse the thread ID soon enough for this to be a problem? If yes, how about we reset the os_id in the ThreadRegistry when a thread ends (for Linux, and keep the value for Darwin)?

[dvyukov]

lib/tsan/rtl/tsan_debugging.cc

168

tsan_locate_address(addr) ... returns region name, start address, block size
tsan_get_alloc_stack(addr) ... returns trace, thread ID

sounds better, more orthogonal and some use cases may not need stack/thread

181

Linux reuses PIDs FIFO, but it still reuses them.
On closer inspection, there is a more realistic source of bogus values -- tid's are recycled, and ThreadContext we obtain can be for a different thread. Tid does not uniquely identify ThreadContext, it's tid+epoch that does. But we don't have epoch in MBLock.
So I think it's fine to leave code as is.

[kubamracek]

Updating patch to also add __tsan_locate_address. Adding a testcase.

lib/tsan/rtl/tsan_debugging.cc

 // This file is a part of ThreadSanitizer (TSan), a race detector.
 //
 // TSan debugging API implementation.
 //===----------------------------------------------------------------------===//
 #include "tsan_interface.h"
 #include "tsan_report.h"
 #include "tsan_rtl.h"
 
+#include "sanitizer_common/sanitizer_stackdepot.h"
+
 using namespace __tsan;
 
 static const char *ReportTypeDescription(ReportType typ) {
   if (typ == ReportTypeRace) return "data-race";
   if (typ == ReportTypeVptrRace) return "data-race-vptr";
   if (typ == ReportTypeUseAfterFree) return "heap-use-after-free";
   if (typ == ReportTypeVptrUseAfterFree) return "heap-use-after-free-vptr";
   if (typ == ReportTypeThreadLeak) return "thread-leak";

 
 SANITIZER_INTERFACE_ATTRIBUTE
 int __tsan_get_report_unique_tid(void *report, uptr idx, int *tid) {
   const ReportDesc *rep = (ReportDesc *)report;
   CHECK_LT(idx, rep->unique_tids.Size());
   *tid = rep->unique_tids[idx];
   return 1;
 }
+
+SANITIZER_INTERFACE_ATTRIBUTE
+int __tsan_get_alloc_stack(uptr addr, uptr *trace, uptr size, int *thread_id,
+                           uptr *os_id) {
+  MBlock *b = 0;
+  Allocator *a = allocator();
+  if (a->PointerIsMine((void *)addr)) {
+    void *block_begin = a->GetBlockBegin((void *)addr);
+    if (block_begin) b = ctx->metamap.GetBlock((uptr)block_begin);
+  }
+  if (b == 0) return 0;
+
+  *thread_id = b->tid;
+  // No locking.  This is supposed to be called from within the debugger when
+  // other threads are stopped.
+  ThreadContextBase *tctx = ctx->thread_registry->GetThreadLocked(b->tid);
+  *os_id = tctx->os_id;
+
+  StackTrace stack = StackDepotGet(b->stk);
+  size = Min(size, (uptr)stack.size);
+  for (uptr i = 0; i < size; i++) trace[i] = stack.trace[stack.size - i - 1];
+  return size;
+}

lib/tsan/rtl/tsan_interface.h

 int __tsan_get_report_thread(void *report, uptr idx, int *tid, uptr *os_id,
                              int *running, const char **name, int *parent_tid,
                              void **trace, uptr trace_size);
 
 // Returns information about unique thread IDs included in the report.
 SANITIZER_INTERFACE_ATTRIBUTE
 int __tsan_get_report_unique_tid(void *report, uptr idx, int *tid);
 
+SANITIZER_INTERFACE_ATTRIBUTE
+int __tsan_get_alloc_stack(uptr addr, uptr *trace, uptr size, int *thread_id,
+                           uptr *os_id);
+
 #endif  // SANITIZER_GO
 
 #ifdef __cplusplus
 }  // extern "C"
 #endif
 
 namespace __tsan {
 

test/tsan/debug_alloc_stack.cc

+// RUN: %clangxx_tsan -O0 %s -o %t
+// RUN: env %env_tsan_opts=stack_trace_format=DEFAULT %deflake %run %t 2>&1 | FileCheck %s
+
+#include "test.h"
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#if !__APPLE__
+#include <sys/types.h>
+#endif
+
+extern "C" int __tsan_get_alloc_stack(void *addr, void **trace, size_t size,
+                                      int *thread_id, void *os_id);
+
+char *mem;
+void alloc_func() { mem = (char *)malloc(10); }
+
+void *AllocThread(void *context) {
+  uint64_t tid;
+#if __APPLE__
+  pthread_threadid_np(NULL, &tid);
+#else
+  tid = gettid();
+#endif
+  fprintf(stderr, "alloc stack thread os id = 0x%llx\n", tid);
+  // CHECK: alloc stack thread os id = [[THREAD_OS_ID:0x[0-9a-f]+]]
+  alloc_func();
+  return NULL;
+}
+
+void *RaceThread(void *context) {
+  *mem = 'a';
+  barrier_wait(&barrier);
+  return NULL;
+}
+
+int main() {
+  pthread_t t;
+  barrier_init(&barrier, 2);
+
+  pthread_create(&t, NULL, AllocThread, NULL);
+  pthread_join(t, NULL);
+
+  void *trace[100];
+  size_t num_frames = 100;
+  int thread_id;
+  void *thread_os_id;
+  num_frames =
+      __tsan_get_alloc_stack(mem, trace, num_frames, &thread_id, &thread_os_id);
+
+  fprintf(stderr, "alloc stack retval %s\n",
+          (num_frames > 0 && num_frames < 10) ? "ok" : "");
+  // CHECK: alloc stack retval ok
+  fprintf(stderr, "thread id = %d\n", thread_id);
+  // CHECK: thread id = 1
+  fprintf(stderr, "thread os id = 0x%llx\n", (uint64_t)thread_os_id);
+  // CHECK: thread os id = [[THREAD_OS_ID]]
+  fprintf(stderr, "%p\n", trace[0]);
+  // CHECK: [[ALLOC_FRAME_0:0x[0-9a-f]+]]
+  fprintf(stderr, "%p\n", trace[1]);
+  // CHECK: [[ALLOC_FRAME_1:0x[0-9a-f]+]]
+  fprintf(stderr, "%p\n", trace[2]);
+  // CHECK: [[ALLOC_FRAME_2:0x[0-9a-f]+]]
+
+  pthread_create(&t, NULL, RaceThread, NULL);
+  barrier_wait(&barrier);
+  mem[0] = 'b';
+  pthread_join(t, NULL);
+
+  free(mem);
+
+  return 0;
+}
+
+// CHECK: WARNING: ThreadSanitizer: data race
+// CHECK: Location is heap block of size 10 at {{.*}} allocated by thread T1
+// CHECK: #0 [[ALLOC_FRAME_0]]
+// CHECK: #1 [[ALLOC_FRAME_1]] in alloc_func
+// CHECK: #2 [[ALLOC_FRAME_2]] in AllocThread