tombstoned: don't generate tombstones for native backtraces.

Previously, if an intercept ends before we ask for a file descriptor
when doing a backtrace, we'll create a tombstone file instead.

Bug: http://b/114139908
Bug: http://b/115349586
Test: debuggerd_test32
Change-Id: I23c7bb8ae5a982a4374a862d0a4f17bee03eb1d9

2 files changed, 47 insertions, 2 deletions

diff --git a/debuggerd/debuggerd_test.cpp b/debuggerd/debuggerd_test.cpp
index 388facb45..bea8b43ca 100644
--- a/debuggerd/debuggerd_test.cpp
+++ b/debuggerd/debuggerd_test.cpp
@@ -37,6 +37,7 @@
 #include <android-base/macros.h>
 #include <android-base/parseint.h>
 #include <android-base/properties.h>
+#include <android-base/stringprintf.h>
 #include <android-base/strings.h>
 #include <android-base/test_utils.h>
 #include <android-base/unique_fd.h>
@@ -1053,3 +1054,42 @@ TEST(tombstoned, intercept_any) {
   ASSERT_TRUE(android::base::ReadFully(output_fd.get(), outbuf, sizeof(outbuf)));
   ASSERT_STREQ("any", outbuf);
 }
+
+TEST(tombstoned, interceptless_backtrace) {
+  // Generate 50 backtraces, and then check to see that we haven't created 50 new tombstones.
+  auto get_tombstone_timestamps = []() -> std::map<int, time_t> {
+    std::map<int, time_t> result;
+    for (int i = 0; i < 99; ++i) {
+      std::string path = android::base::StringPrintf("/data/tombstones/tombstone_%02d", i);
+      struct stat st;
+      if (stat(path.c_str(), &st) == 0) {
+        result[i] = st.st_mtim.tv_sec;
+      }
+    }
+    return result;
+  };
+
+  auto before = get_tombstone_timestamps();
+  for (int i = 0; i < 50; ++i) {
+    raise_debugger_signal(kDebuggerdNativeBacktrace);
+  }
+  auto after = get_tombstone_timestamps();
+
+  int diff = 0;
+  for (int i = 0; i < 99; ++i) {
+    if (after.count(i) == 0) {
+      continue;
+    }
+    if (before.count(i) == 0) {
+      ++diff;
+      continue;
+    }
+    if (before[i] != after[i]) {
+      ++diff;
+    }
+  }
+
+  // We can't be sure that nothing's crash looping in the background.
+  // This should be good enough, though...
+  ASSERT_LT(diff, 10) << "too many new tombstones; is something crashing in the background?";
+}
diff --git a/debuggerd/tombstoned/tombstoned.cpp b/debuggerd/tombstoned/tombstoned.cpp
index 15ae40624..ad9206702 100644
--- a/debuggerd/tombstoned/tombstoned.cpp
+++ b/debuggerd/tombstoned/tombstoned.cpp
@@ -212,8 +212,13 @@ static void perform_request(Crash* crash) {
   bool intercepted =
       intercept_manager->GetIntercept(crash->crash_pid, crash->crash_type, &output_fd);
   if (!intercepted) {
-    std::tie(crash->crash_tombstone_path, output_fd) = CrashQueue::for_crash(crash)->get_output();
-    crash->crash_tombstone_fd.reset(dup(output_fd.get()));
+    if (crash->crash_type == kDebuggerdNativeBacktrace) {
+      // Don't generate tombstones for native backtrace requests.
+      output_fd.reset(open("/dev/null", O_WRONLY | O_CLOEXEC));
+    } else {
+      std::tie(crash->crash_tombstone_path, output_fd) = CrashQueue::for_crash(crash)->get_output();
+      crash->crash_tombstone_fd.reset(dup(output_fd.get()));
+    }
   }
 
   TombstonedCrashPacket response = {