[sanitizer] VReport thread status for failed PTRACE_ATTACH

[vitalybuka]

Such threads can cause false leak reports,
but often it's hard to diagnose the reason of
failed PTRACE_ATTACH. Maybe we can find
a clue from /proc/*/task/*/status

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Vitaly Buka (vitalybuka)

Changes

Such threads can cause false leak reports,
but often it's hard to diagnose the reason of
failed PTRACE_ATTACH. Maybe we can find
a clue from /proc/*/task/*/status

---

Full diff: https://github.com/llvm/llvm-project/pull/111901.diff

1 Files Affected:

• (modified) compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp (+8)

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
index d9f803a276dadc..a42f6ab1241796 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
@@ -148,6 +148,14 @@ bool ThreadSuspender::SuspendThread(tid_t tid) {
     // Log this event and move on.
     VReport(1, "Could not attach to thread %zu (errno %d).\n", (uptr)tid,
             pterrno);
+    if (common_flags()->verbosity >= 2) {
+      InternalScopedString path;
+      path.AppendF("/proc/%d/task/%llu/status", pid_, tid);
+      InternalMmapVector<char> buffer;
+      ReadFileToVector(path.data(), &buffer);
+      buffer.push_back(0);
+      VReport(2, "%s: %s\n", path.data(), buffer.data());
+    }
     return false;
   } else {
     VReport(2, "Attached to thread %zu.\n", (uptr)tid);